Reproductions supplied by EDRS are the best that can be madeRichard Dexter, John F. Kennedy High...

DOCUMENT RESUME

ED 477 259 SE 067 620

AUTHOR Huheey, James; Sandoval, Amado

TITLE Diversity and Periodicity: An Inorganic Chemistry Module.Teacher's Guide.

ISBN ISBN-06-561221-3PUB DATE 1978-00-00NOTE 83p.; Produced by the Chemistry Association of Maryland. For

student book, see SE 067 619. For other modules in series,see SE 067 618-630.

PUB TYPE Books (010) Guides Classroom Teacher (052)EDRS PRICE EDRS Price MF01/PC04 Plus Postage.DESCRIPTORS *Chemical Nomenclature; Chemistry; Curriculum Design;

Instructional Materials; Interdisciplinary Approach; ScienceInstruction; Secondary Education

ABSTRACT

This teacher's guide is designed to provide science teacherswith the necessary guidance and suggestions for teaching inorganic chemistry.The material in this book can be integrated with the other modules in asequence that helps students to see that chemistry is a unified science.Contents include: (1) "Periodicity: A Chemical Calendar"; (2) "StructuralChemistry of Metals and Their Compounds"; (3) "Inorganic Molecules"; (4)

"Acids and Bases"; (5) "Chemistry of the Transition Elements"; and (6)"Bioinorganic Chemistry". (KHR)

Reproductions supplied by EDRS are the best that can be madefrom the original document.

interdisciplinaryapproachesto chemistry

TEACHER'S GUIDE

DIVERSITY AND PERIODICITYAN INORGANIC CHEMISTRY MODULE

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IAC PROJECT TEAMDirectors of IAC:Marjorie Gardner, 1971-73, 1976Henry Heikkinen, 1973-76

Revision Coordinator:Alan DeGennaro

MC MODULAR CHEMISTRY PROGRAM MODULE U THOk S

REACTIONS AND REASON: Gordon Atkinson, Henry HeikkinenAn Introductory Chemistry Module

DIVERSITY AND PERIODICITY: James HuheeyAn Inorganic Chemistry Module

FORM AND FUNCTION: Bruce Jarvis, Paul MazzocchiAn Organic Chemistry Module

MOLECULES IN LIVING SYSTEMS: David Martin, Joseph SampugnaA Biochemistry Module

THE HEART OF MATTER: Vic ViolaA Nuclear Chemistry Module

THE DELICATE BALANCE: Glen Gordon, William KeiferAn Energy and the Environment Chemistry Module

COMMUNITIES OF MOLECULES: Howard DeVoeA Physical Chemistry Module

Teacher's Guides Teacher's Guide Coordinators:(available for each module) Robert Hearle, Amado Sandoval

interdisciplinaryjapproachesto chemistry

lacTEACHER'S GUIDE

DIVERSITY AND PERIODICITYAN INORGANIC CHEMISTRY MODULE

James HuheeyAmado Sandoval

[fl1817

Harper & Row, PublishersNewYork Hagerstown San Francisco London

AUTHORS

TEACHER'S GUIDE

DIVERSITY AND PERIODICITY:AN INORGANIC CHEMISTRY MODULE

JAMES HUHEEY

When not driving his red and white truck up and down the mountainsof western North Carolina in search of "the perfect salamander," ratchet-jawing with the 18-wheelers out on "that ol' boulevard" with his CB, orpounding a typewriter to keep his editor happy, Jim Huheey finds timeto do some of the other things inorganic chemists do: research on elec-tronegativity and related topics, lecture preparations, faculty meetings,Sunday afternoon football games, etc., etc. Ever since he joined the Uni-versity of Maryland from the University of Illinois via Worcester Polytech,Jim Huheey has been a major contributor to the mainstream of the de-partment life. Characterizing himself (in a friendly needle to the organicchemists) as a chemist of the other 105 elements, his work in the pasthas been geared mostly to the college and university levels. Lately hehas extended his range to encompass high school as well.

Capping his many achievements, in 1971 he received the Young Chem-istry Teachers' Award sponsored by the District of Columbia division ofthe American Institute of Chemists; and in 1972 his publishers broughtout his second book, a college text titled Inorganic Chemistry: Principlesof Structure and Reactivity.

AMADO SANDOVAL

Since 1969 when he went to the University of Maryland as a ChemistryTeaching Associate, Amado (Pepe) Sandoval has been involved withchemical education in the Maryland-D.C. area: first as a teaching .38-sociate, then as a student-teacher supervisor, teacher workshop instruc-tor, and now as a teacher at Wilde Lake and Centennial High Schoolsin Howard Co., Maryland. While at Wilde Lake High School he hasbeen involved in the development of the IAC program where he devel-oped teacher guide material and independent study guides for all IACmodules.

Copyright © 1978 by Chemistry Associates of Maryland, Inc.All rights reserved.Printed in the United States of America.No part of this publication may be reproduced in any form or by any means, photographic, electrostatic or mechanical, or by anyinformation storage and retrieval system or other method, for any use, without written permission from the publisher.

STANDARD BOOK NUMBER 06-561221-3

89012MU0987654321

II

6BEST COPY AVAILABLE

Contents

Introducing Diversity and PeriodicitySpecial Features in the Student ModuleManaging the LaboratoryEvaluating Student PerformanceModule ConceptsModule ObjectivesTeaching Diversity and Periodicity

INTRODUCING INORGANIC CHEMISTRY

PERIODICITY: A CHEMICAL CALENDAR

I-1 Chemical Cycles1-2 Ultraman vs. Flintstones1-3 Periodic Properties1-4 Periodicity/Miniexperiment1-5 Chemistry's Crystal Ball1-6 The Hydrogen and Helium Puzzle1-7 Keeping Up with the Trends1-8 Family Relationships1-9 All in the FamilylMiniexperimentI-10 Gainers and Losers

STRUCTURAL CHEMISTRY OF METALSAND THEIR COMPOUNDS

1-11 Why Are Metals "Metallic"?1-12 Who's Who?IMiniexperiment1-13 How's Your Coordination?1-14 Becoming an Efficiency Expert/Experiment1-15 Metallic Properties: Look Again1-16 Growth Is the Name of the Garnet Miniexperiment1-17 Getting a Charge1-18 Attracting Opposites/Miniexperiment1-19 Packing lonslExperitnent1-20 The Effects of Hanging TogetherlMiniexperiment

INORGANIC MOLECULES

1-21 The Covalent Bond: Share or Else!1-22 Molecular Shape1-23 Structures of Molecules/ Experiment1-24 A Matter of Life and Breath1-25 Some Important Molecules

ACIDS AND BASES

1-26 Getting Down to Basics (and Acidics)1-27 Household Acids and Basest Experiment1-28 Acids and Bases Go to Work1-29 What's in a Name?

6

2346

11

11

11

12121212141414151820

23

23232424333335353637

38

3839404243

45

45454647

iii

CHEMISTRY OF THE TRANSITION ELEMENTS 48

1-30 You Can't Lose for Winning 481-31 Coordination Chemistry! Hold on! 491-32 Get Coordinated!/Experiment 491-33 Look to the Rainbow 511-34 Using Coordination Compounds 531-35 Bathtub Rings and Things/ Miniexperitnent 541-36 Water Softening/Min iexperimen t 551-37 Solvent Extraction/Chemical Tweezers 551-38 Cation Lib/Min iexperimen t 561-39 Knock, Knock! What's There? 571-40 Get the Lead Outil Miniexperiment 57

BIOINORGANIC CHEMISTRY 58

1-41 Bioinorganic's: The "Bad News" 591-42 Bioinorganics: The "Good News" 591-43 Enzymes: Chemical Meat Cleavers 591-44 Take a Deep Breath 601-45 Redox Action 60

A SUMMING UP 62

APPENDIX 63

Safety 63Suggested Readings 64Module Tests 64

Knowledge-Centered Module Test 67Skill-Centered Module Test 68

Materials List 70Index 73Table of International Relative Atomic Masses 74Periodic Table of the Elements 75

7

iv

AcknowledgmentsIAC Test Teachers

Linwood Adams, Bowie High School, Prince George'sCounty, MD

Thomas Antonicci, Archbishop Curley High School, Balti-more, MD

Nicholas Baccala, Milford Mill High School, BaltimoreCounty, MD

Rosemary Behrens, Bethesda-Chevy Chase High School,Montgomery County, MD

Virginia Blair, Holton-Arms School, Bethesda, MDEthyl duBois, Crossland and Oxon Hill High Schools, Prince

George's County, MDSally Buckler, High Point High School, Prince George's

County, MDTherese Butler, Bowie High School, Prince George's

County, MDKevin Castner, Bowie High School, Prince George's

County, MDRobert Cooke, Kenwood High School, Baltimore County, MDWilmer Cooksey, Woodrow Wilson High School, Wash-

ington, DCFrank Cox, Parkville High School, Baltimore County, MDRichard Dexter, John F. Kennedy High School, Montgomery

County, MDElizabeth Donaldson, John F. Kennedy High School, Mont-

gomery County, MDClair Douthitt, Chief Sealth High School, Seattle, WALawrence Ferguson, Milford Mill High School, Baltimore

County, MDHarry Gemberling, Du Val and Eleanor Roosevelt High

Schools, Prince George's County, MDAlan Goldstein, Laurel High School, Prince George's

County, MDMarjorie Green, McLean High School, Fairfax County, VAWilliam Guthrie, Parkdale High School, Prince George's

County, MDLaura Hack, Annapolis High School, Annapolis, MDMargaret Henderson, Fort Hunt High School, Fairfax

County, VAMartina Howe, Bethesda-Chevy Chase High School, Mont-

gomery County, MDGlendal Jenkins, Surrattsville High School, Prince George's

County, MDMartin Johnson, Bowie High School, Prince George's

County, MDHarold Koch, Southwest High School, Minneapolis, MNJane Koran, Arundel High School, Anne Arundel County, MDMarilyn Lucas, Euclid High School, Euclid, OHDavid McElroy, Albert Einstein High School, Montgomery

County, MD

IAC 1978 Revision Teacher Consultants

Robert Andrews, Bothell High School, Bothell, Washington;Minard Bakken, The Prairie School, Racine, Wisconsin; ErvinForgy, J. I. Case High School, Racine, Wisconsin; MargaretHenley, Kennedy High School, Granada Hills, California;Bernard Hermanson, Sumner Community Schools, Sumner,Iowa; Merlin Iverson, Mason City High School, Mason City,Iowa; Harold Koch, Southwest High School, Minneapolis,Minnesota; Philippe Lemieux, Lincoln-Sudbury Regional

Marilu McGoldrick, Wilde Lake High School, HowardCounty, MD

John Malek, Meade High School, Ft. Meade, MDRobert Mier, Bowie and Eleanor Roosevelt High Schools,

Prince George's County, MDGeorge Milne, Oxon Hill High School, Prince George's

County, MDDavid Myers, Crossland High School, Prince George's

County, MDGeorge Newett, High Point High School, Prince George's

County, MDDaniel Noval, Patapsco High School, Baltimore County, MDM. Gail Nussbaum, Northwestern High School, Prince

George's County, MDElena Pisciotta, Parkdale High School, Prince George's

County, MDAndrew Pogan, Poolesville High School, Montgomery

County, MDCharles Raynor, Dulaney High School, Baltimore County, MDRosemary Reimer Shaw, Montgomery Blair High School,

Montgomery County, MDE. G. Rohde, Academy of the Holy Names, Silver Spring, MDDoris Sandoval, Springbrook High School, Montgomery

County, MDEarl Shaw, Damascus High School, Montgomery County, MDGeorge Smeller, Robert Peary High School, Montgomery

County, MDHoward Smith, Parkville High School, Baltimore County, MDLarry Sobotka, Parkville High School, Baltimore County, MDRoger Tatum, Takoma Academy, Takoma Park, MDYvette Thivierge, Fairmont Heights High School, Prince

George's County, MDBarbara Tracey, Bishop McNamara High School, Forest-

ville, MDRonald Trivane, Pikesville High School, Baltimore

County, MDJeanne Vaughn, Governor Thomas Johnson High School,

Frederick County, MDDrew Wolfe, Randallstown High School, Baltimore

County, MDPauline Wood, Springbrook High School, Montgomery

County, MDJames Woodward, Walt Whitman High School, Montgomery

County, MDClement Zidick, Dimond and Wasilla High Schools, Anchor-

age, AK

High School, Acton, Massachusetts; Robert Sherwood, NewPalestine High School, New Palestine, Indiana; KennethSpengler, Palatine High School, Palatine, Illinois; David Tanis,Holland Christian High School, Holland, Michigan; DaleWolfgram, Grand Blanc High School, Grand Blanc, Michigan;Clement Zidick, Dimond and Wasilla High Schools, Anchor-age, Alaska

8

Introducing Diversity and PeriodicityDiversity and Periodicity: An Inorganic ChemistryModule illustrates one of the many facets of mod-ern chemistry. As with all of the other IAC mod-ules, it is written to stand alone, requiring onlythe prior coverage of Reactions and Reason: AnIntroductory Chemistry Module. You will also findthat the material here can be integrated with theother modules in a sequence that helps the stu-dent to see that chemistry is a unified, thoughmultifaceted, science.

When should this module be taught? SomeIAC teachers use it early with good results, andothers work it in equally satisfactorily after teach-ing several other modules. We leave the timingto you. We would emphasize, however, that theold notion that inorganic chemistry is "basic" or"simple," and that therefore it should be taughtearly, is spurious. The idea stems from the daywhen the first course in college chemistry wascalled "inorganic chemistry" and consisted ofmemorizing some reactions of various elements.As the IAC team has tried to show in all of thesemodules, there are basic and fundamental con-cepts in every branch of chemistry, and thereare very sophisticated, even philosophical, con-cepts to be derived from all areas.

As we worked on Diversity and Periodicity, inaddition to the desire to make the material in-teresting and attractive, we found ourselves ask-ing the questions: What do inorganic chemistsdo? How do they go about their work? Howdoes their work impinge upon the society inwhich they live? We have tried to answer thesequestions for the student, for we feel that an

understanding of what a chemist does and thinksis as important a part of the student's educationas knowing the product of a particular reaction.In fact, long after most of your students havelost active contact with chemistry (only a verysmall fraction will become chemists), they willbe well-informed and clear-thinking citizensmaking decisions on this nation's priorities,many of them dealing with science.

This module covers old favorites of inorganicchemistry, including discussion of ammonia andsulfur trioxide and the titration of acids andbases. In addition, there are syntheses that maybe new to you in a high-school context, such asthe preparation of coordination compounds, avery important class of inorganic compounds.You may also be surprised to be discussing mole-cules such as hemoglobin in the context of inor-ganic chemistry. Even old war-horsesNH,and SO,, for instanceare considered in lightof current and related topics, such as nitrogen-fixation (by plants and people) and air pollution,as well as more basic concepts. We have notbroadened our scope in this way to prove howclever we are; all of these topicscoordinationcompounds, hemoglobin, nitrogen-fixation, andair pollutionare of paramount concern to inor-ganic chemistry today.

We have tried to provide you with the neces-sary guidance and suggestions for teaching thismodule. We hope you will enjoy teaching Diver-sity and Periodicity: An Inorganic Chemistry Moduleand that your students will enjoy working with it.

Special Features in theStudent Module

Metric System Le Systeme Internationale (SI)is used throughout the IAC program. As you work

9

with this module, you may wish to review somepoints of the metric system as presented in Reac-tions and Reason: An Introductory Chemistry Mod-ule (see section A-8 and Appendix II). There isa metric units chart in the appendix of the studentmodule that students can easily refer to.

1

Time Machine A feature we call the Time Machineappears in the IAC modules in order to showchemistry in a broader context. For some stu-dents, this may provide a handle on particularaspects of chemistry by establishing the social-cultural-political framework in which significantprogress was made in chemistry. Students mayenjoy suggesting other events in chemistryaround which to create Time Machines of theirown.

Cartoons A popular feature of the IAC programis the use of chemistry cartoons. These cartoonsgive students a chance to remember specificpoints of chemistry in another important wayby humor. Suggest that your students createother chemistry cartoons for their classmates toenjoy.

Safety Laboratory safety is a special concern inany chemistry course. In addition to includingsafety discussion and guidelines in the appendixof each student module and teacher's guide ex-periments have been developed in a way toeliminate potentially dangerous chemicals or pro-cedures. Moreover, each experiment that mightpresent a hazardthrough fumes, corrosivechemicals, use of a flame, or other conditionshas been marked with a safety symbol to alertstudents and teachers to use added, reasonablecaution. Caution statements, in bold type, alsoappear in experiments to specifically instruct thestudent on the care required.

Managing the Laboratory

In the teacher's guide, hints and suggestions aregiven for managing each experiment in the labora-tory. Share as many of these hints as possiblewith your students. Allow them to participatefully in successful laboratory management. Makesure that you rotate assignments so that all stu-dents get a chance to experience this type ofparticipation.

2

Selected Readings Articles and books that tie inwith the topics discussed in the IAC programhave been listed in the appendix of the studentmodule as well as in the teacher's guide. Encour-age your students to use this section. You maywish to suggest other material that you yourselfhave found interesting and enjoyable.

Illustrations and Photographs The module isextensively illustrated to provide relevant andstimulating visual material to enable students torelate chemistry to everyday life, as well as toprovide material for provocative discussion. Inusing some of these illustrations, it is not theintention of IAC to endorse any particular prod-uct or brand, but only to relate chemistry to lifeoutside the classroom. As you proceed througheach section, encourage students to collect, dis-play, and discuss photos and illustrations thatprovoke further discussion.

Questions A number of questions have beeninterspersed throughout the student module,in addition to the questions that are naturallybuilt into the narratives and the laboratory ex-periments. You will find some of these in specif-ically marked sections in the student module.These questions can be used in a variety of waysas you see fit. They are not planned as testsremember, the IAC program is designed so thatmastery of the content and skills can be achievedthrough the repeated reinforcement of ideas andprocedures encountered by students as they pro-gress through the various modules.

Preparations and Supplies Student aides can behelpful in preparing solutions, labeling and fillingbottles, cleaning glassware, and testing experi-ments. (You should still test each experiment inthe module to determine if any revision is neededto meet the needs of your students.)

Cleaning Up Involve your students in puttingaway equipment, washing up glassware, andstoring material for the next time it is to be used.

l.0

Taking care of equipment is part of responsi-bilities we seek to foster in the students' outsideenvironment.

Laboratory Reports You may have your ownmethods of student reporting. We are includingsome of the suggestions that IAC teachers havefound successful in the past. It is helpful for stu-dents to keep a laboratory notebook. A quadrille-ruled laboratory notebook with a sheet of carbonpaper allows a student to produce two data sheetsand report summary copies. One copy of eachpage can be permanently retained in the note-book, while the duplicate copy can be submittedfor evaluation or tabulation.

A realistic view of laboratory work suggeststhat, in the most fundamental sense, there are no"wrong" laboratory results. All students obtainresults consistent with particular experimentalconditions (either correct or incorrect) that theyestablish. Careful work will yield more preciseresults, of course. Encourage each student to takepersonal pride in experimental work. If studentsdisagree on a result, discuss the factors that mightaccount for the difference. A student who pro-vides a thoughtful analysis of why a particularresult turned out to be "different" (incompletedrying, a portion of the original sample wasspilled, etc.) deserves credit for such inter-pretation.

Laboratory Safety To use the IAC programsafely, you should become thoroughly familiarwith all student activities in the laboratory. Doall the experiments and carry out all the demon-strations yourself before presenting them to yourclass. We have tested each experiment and havesuggested the use of chemicals that present theleast chance of a problem in laboratory safety.This teacher's guide has many suggestions forhelping you provide your students with safelaboratory experiences. Have the students readthe safety section in the appendix of the studentmodule. Conduct a brief review of laboratorysafety before allowing them to encounter theirfirst laboratory experience in this module. Reviewsafety procedures when necessary and discusscaution and safety each time a safety symbolappears in the student text.

Materials for IAC In light of increasing costs forequipment and supplies, as well as decreasingschool budgets, we have tried to produce a ma-terials list that reflects only the quantities neededto do the experiments, with minimal surplus.Thus, the laboratory preparation sections containinstructions for only a 10-20 percent surplus ofreagents. Add enough materials for studentrepeats and preparations errors.

Evaluating Student Performance

There are many ways of evaluating your stu-dents' performances. One of the most importantforms of evaluation is observing your studentsas they proceed through the IAC program. IAChas developed skill tests and knowledge testsfor use with this module. These test items havebeen suggested and tested by IAC classroom

chemistry teachers. You are encouraged to addthese to your own means of student evaluation.

In addition to the questions incorporated in thestudent module text and illustration captions,there are suggestions for evaluation at the endof each module section in the teacher's guide.The module tests are at the end of the teacher'sguide. Answers to all of the evaluation items areincluded to help you in your classroom discus-ion and evaluation.

11 3

Module Concepts

INORGANIC CHEMISTRY

Inorganic chemistry is a study of the propertiesof all the elements.

Each element is unique, yet it is possible toprovide a unifying description of all elements.


Many properties of elements recur in fixedcycles; these are called periodic properties.

The periodic chart displays the elements ar-ranged by their increasing atomic number.

Elements may be divided into two groupsmetals and nonmetals.

Knowledge of periodic properties enableschemists to make predictions about the physicaland chemical properties of elements.

All elements occurring in a single column ofthe periodic table have similar properties; theyform a family of elements.

Each family of elements differs from the othersin the tendency to gain or lose electrons; this isrecognized in the combining ability of theseelements.

STRUCTURAL CHEMISTRY OF METALS ANDTHEIR COMPOUNDS

The physical properties of metals are relatedto the bonding between atoms and the latticestructure of the solid.

Different lattice structures may have a greaternumber of atoms of the same size that could bepacked in a given volume.

The physical properties of ionic compounds arerelated to the bonding between ions and thelattice structure of the solid.

Similar ionic compounds may have differentlattice structures.

INORGANIC MOLECULES

Inorganic molecules can be formed by thecovalent bonding between nonmetallic elements.

Physical and chemical properties of moleculesare related to their geometry and structure; thesemay be influenced by nonbonding electron pairs.

The partial electronic charges upon a polarmolecule may attract other polar molecules andform a "bond," such as the hydrogen bond.

4

The synthesis of some nonmetallic compoundswould not be feasible without the use of catalysts.

ACIDS AND BASES

The properties of an acid can be looked uponas being opposite to the properties of a base.

One definition of an acid is a compound thatdonates hydrogen ions to water in solution toform hydronium ions, H30+.

A base is an acceptor of hydrogen ions; basicsolutions result when the solute removes hydro-gen ions from water molecules, leaving hydroxideions behind.

Acids and bases react with each other to neu-tralize the properties of both; water and salt areneutralization products.

Acid-base neutralization reactions are quan-titative.

Acids and bases are present in many house-hold cleaners because of their powerful chemicalaction.

A Lewis acid is an electron pair acceptor anda Lewis base an electron pair donor.

CHEMISTRY OF THE TRANSITION ELEMENTS

Transition elements occupy a specific area ofthe periodic table that lies between the alkali andalkaline earth metals (Groups IA and IIA) andthe remaining representative metals and non-metals (Groups IIIAVIVA).

The transition metals tend to lose electrons,forming positive ions, and in doing so are oxidized.

Transition or other metallic ions may gainelectrons to become metal atoms and in doingso are reduced.

Transition metals may be oxidized or reducedin more than one step; that is, they usually havemore than one stable oxidation state.

When accepting electrons, transition metal ionsact as oxidizing agents; when giving up electrons,they act as reducing agents.

A transition metal ion may function as a Lewisacid, accept electron pairs from a ligand, andform complexes (coordination compounds) bycovalent bonding.

Molecules or anions able to donate an electronpair (a Lewis base) may act as ligands.

Coordination compounds often display charac-teristic properties, such as colors and geometry.

12

Metallic ions may be removed from furtherchemical reaction by formation of coordinationcomplexes.

Solvent extraction may be used to effect theseparation of metals. A desired metal reacts witha particular ligand to form a complex that has agreater solubility in one solvent than another.

The distinct color of coordination compoundsmay be used as a specific test for the presenceof a given chemical species.

BIOINORGANIC CHEMISTRY

Bioinorganic chemistry is concerned with therole of inorganic chemicals in biological systems.

The majority of environmental pollutants areinorganic in nature.

There are about 20 elements essential to livingorganisms; some of these are needed in traceamounts.

Metalloenzymes contain specific metal ions.These may be displaced by other metal ions that"poison" the enzyme.

The oxygen transport to tissues of higheranimals involves a coordination compound of theligand oxygen (02) and the iron ion (Fe2+) in theheme group.

The driving force of living systems is the oxida-tion of carbohydrates and similar substances.Many redox reactions that occur in the electrontransport system are made possible by enzymesthat contain metallic ions.

A SUMMING UP

Alchemy and the processing of metallic oresprovided the "roots" for inorganic chemistry.Inorganic chemistry overlaps other areas of chem-istry, such as analytical, physical, and organicchemistry, and recently has extended into newareas, such as bioinorganic chemistry.

135

Module Objectives

We have attempted to group module objectives inthree broad categories: concept-centered, attitude-centered, and skill-centered. The categories arenot mutually exclusive; there is considerable over-lap. The conditions for accomplishing each objec-tive are not given, since they can easily be foundin the respective section in the module. Note alsothat concept and skill objectives are more specificthan those in the affective domain. It is very dif-ficult to classify objectives in this way, but we

Concept-Centered Objectives

have been encouraged to do so by classroomteachers, who have helped in this difficult task.

The objectives identified here should provideyou with a useful starting point in clarifying yourown goals in teaching this module. We encourageyou to identify alternative objectives, using thislist as a point of departure. Assessment items canbe found at the end of major sections in the stu-dent module in the form of Problems. OtherEvaluation Items are included after each major sec-tion of this guide and in the form of module testsfor knowledge and skill objectives located in theteacher's guide appendix.

Attitude-Centered Objectives Skill-Centered Objectives

INTRODUCING INORGANIC CHEMISTRY

Give a definition of inorganicchemistry and relate this to theother areas of chemistry.

Realize that the study of theproperties of elements enables thechemist to group them in a mannerthat might predict the propertiesand existence of other elementsthat are not yet discovered.


1-1

Give examples of cyclic eventsthat "predict" weekly or monthlybehavior.

1-2

Identify the characteristicproperties of metals andnonmetals.

Distinguish between metals andnonmetals on the basis of theirphysical properties.

Give examples of metals,nonmetals, and metalloids that areuseful because of malleability,ductility, or absence of thesecharacteristics.

1-3

Describe the increase ordecrease in ionization energy as aperiodic function.

6

Sense the beauty of the orderof the universe as exemplified bythe periodic law.

Recognize the usefulness ofbeing able to predict properties ofchemical elements.

Be aware that nature does notalways allow us to "pigeonhole"things, whether they be elementsor people.

Enjoy the humor to be found inotherwise serious material by usingcartoons and puns.

Discuss the "amazing accuracy"of Mendeleev's predictions as wellas their importance to the field ofchemistry.

Appreciate the usefulness ofhaving a unifying theme such asthe periodic law in inorganicchemistry or any science.

14

1-4

Graph atomic number versusionization energy data.

1-6

Outline and identify the mainsections of a standard periodictable.

I -9

Determine relative chemicalreactivity of the halogens throughredox reactions.

Concept-Centered Objectives Attitude-Centered Objectives Skill-Centered Objectives

1-4

Determine the relation betweenionization energy and atomicnumber in a chemical family anda chemical period.

Point out the trends of ionizationenergy changes within differentperiods and groups of elements.

1-7

Provide an explanation for theincrease in length of the repeatingcycle with the addition of thetransition elements.

1-8

Predict an element's relativechemical reactivity based on theposition of the element in theperiodic table.

1-10

Use the relationships in theperiodic table to predict anelement's valence.

Use an element's valence towrite formulas of compounds.

STRUCTURAL CHEMISTRY OF METALS AND THEIR COMPOUNDS

1-11

Explain the malleability ofmetals as a function of theirmetallic bonding.

1-13

Define coordination number andefficiency of packing, and explainhow they are related.

1-14

Determine the coordinationnumber of metallic lattice structures.

1-15

Recognize the relation betweenthe properties of metals and thearrangement of their atoms andelectrons.

Explain the malleability andductility of metals by the ease of"layer glide" in the crystal system.

Recognize that differentmaterials may have differentproperties depending upon theirstructure and bonding.

Appreciate the symmetry andregularity of the various crystalstructures.

Think of the difficulty involvedin magnifying atoms five milliontimes.

Recognize the relationshipbetween the properties of ioniccompounds and their structures.

1i

1-12

Identify and test physicalproperties of metals andnonmetals.

Classify metals and nonmetalson the basis of their physicalproperties.

1-14

Construct three-dimensionalmodels of metallic lattices.

Calculate the packing efficiencyof a metallic lattice structure.

7


1-17

Qualitatively describe ionicbonding. (Note: Ongoing conceptsand objectives are continuouslydeveloped through sections 1-18,1-19, and 1-20.)

1-17, 18, 19Determine the coordination

number of ionic lattice structures.

1-17, 18, 19, 20Determine the common physical

properties of ionic compounds.Compare physical properties of

metals and nonmetals with thoseof ionic compounds.

Explain physical properties ofionic crystals in terms of their ioniclattices.

1-16, 17

Build models of ionic packingsystems.

"Grow" ionic crystals.

1-16, 17, 18Construct three-dimensional

models of ionic lattices.Calculate the packing efficiency

of ionic lattice structures.

INORGANIC MOLECULES

1-21

Identify covalent bonds as thosethat result from the sharing ofelectrons.

Recognize the existence ofmolecules that do not conform tothe octet rule.

1-23

Predict shapes of molecules,including those with nonbondingpairs of electrons.

Determine correct formulas ofsome compounds.

1-24

Relate the physical propertiesof molecules to their moleculargeometry.

1-25

List common important inorganicmolecules and indicate why theyare important.

8

Understand that the chemist candescribe things in many ways,from very sophisticatedmathematical models to simple,everyday words. As long as nomisunderstanding occurs, all of themethods are useful.

Recognize the reasons thatmodel building is important.

Realize and discuss implicationsof changing the geometry, andhence the properties, of essentiallife-supporting molecules.

Appreciate the beauty ofsnowflakes and the relationship oftheir symmetry to molecularproperties.

Realize that whether a chemicalcompound is "good" or "bad"depends upon where we find it.

1-23

Write line formulas formolecules.

Write electron-dot structures formolecules.

Construct ball-and-stick modelsof molecules.

Use magnets as models todetermine molecular geometry.

Use balloons as models todetermine molecular geometry.


ACIDS AND BASES

1-26

Define an acid and write anequation for the dissociation of anacid in H2O.

Define a base and write anequation for the dissociation of abase in H2O.

Write an equation illustrating aneutralization reaction.

Explain the role of an indicatorin the titration process.

Give examples of acids andbases.

1-28

Explain the role of acids andbases in household cleaners.

1-29

Write an acid-base reactionusing electron-dot formulas toillustrate the Lewis principle.

Recognize the importance andnumerous uses of acids and basesin everyday life.

Think of the importance of theanalysis of commercial products,environmental pollutants, andsimilar important chemicals in yourlife.

1-27

Perform an acid-base titration toa correct indicator end point.

Calculate the percent acid orbase in household cleaners.

1-29

State the Lewis definition for anacid and a base.

Give examples of Lewis acidsand bases.

CHEMISTRY OF THE TRANSITION ELEMENTS

1-30

Define oxidation and reductionin terms of electron transfer (gainand loss).

Determine the oxidation state ofelements in compounds and ions.

1-31

Identify the two components thatmake up a coordination compoundor complex.

Define a ligand and give twoexamples.

1-33

List the ligand/metal ratio incommon coordination compounds.

Relate geometry of acoordination complex to its ligand/metal ratio.

1-34

State a useful application ofcoordination compounds.

Appreciate the beautiful colorsof some coordination compounds.

Recognize the increasing use oftransition elements in ourmodern-day society

Appreciate the structural beautyof elements and compounds asviewed under the electronmicroscope.

17

1-30

Write equations to illustratethe oxidation and reduction ofelements.

1-32

Synthesize coordinationcompounds.

1-35

Determine the effect of differentmetal ions on the sudsing abilityof soap solutions.

9


1-37

Explain how "solvent extraction"is used co separate two metalliccoordination compounds.

1-38

Suggest a method to separate amixture of coordination compoundsusing the technique of solventextraction.

1-39

State a useful analyticalapplication of coordinationcompounds.

1-36

Determine the effectiveness ofdifferent chemicals as watersofteners.

1-38

Use solvent extraction toseparate a mixture of compounds.

1-40

Test qualitatively for thepresence or absence of lead in asample.

BIOINORGANIC CHEMISTRY

1-41

Give examples or writeequations to show how inorganicmaterials can act as environmentalpollutants.

1-43

Explain the function of metallicelements in biochemical enzymes.

1-44

Explain the function ofhemoglobin and myoglobin inrespiration.

Explain the ligand-complexingrole of iron in these molecules.

1-45

Give an example of the role ofredox reactions in life processes.

Illustrate by equation the redoxbehavior of Fe in the cytochromec system.

Recognize that many pollutantsare inorganic materials.

Realize the importance ofinorganic materials to survival ofthe living organism.

Recognize that knowledge thechemist obtains in the laboratorycan help us understand processesin living systems, including our ownbodies.

Think of your body as abeautifully complex system ofchemical reactions integrated like agiant chemical factory.

A SUMMING UP

Give examples of the elementsstating how they form complexesthat have important functions ineveryday life.

10

Realize the valuable role thatsome knowledge of inorganicchemistry can play in your life.

18

Teaching Diversity and PeriodicityStudying inorganic chemistry is a serious businessthe study of the other 106 elements, as we havenoted elsewhereyet it offers many opportuni-ties for humor and outright laughter. For betteror worse, this module is rich in cartoons andpuns. We have included some cartoons of ourown, some suggested by IAC students and teach-ers, and others through the courtesy of profes-

sional cartoonists. If they provide a bit of a breakfrom the rigors of learning chemistry, perhapsstudents will be more inclined to try again withsomething they don't understand. As confirmedpunsters, we feel that the worse the puns are, thebetter. More seriously, it is possible that some ofthe puns may serve to stimulate students' curios-ity or to help them remember useful information.

Introducing Inorganic Chemistry

The student first encounters inorganic chemistryin this module in the person of Dmitri Mendeleevand his periodic tables. Mendeleev's predictionswere made more than a century. ago. Studentsmight like to speculate on how long it tookMendeleev to develop his tablesthis might becut short by looking into an encyclopedia or ahistory of chemistryand what the use of a com-puter or even a calculator might have meant tohim. We will look more closely at Mendeleev,beginning in section 1-3.

The fundamental themes with which Men-deleev worked and which are common to all of

inorganic chemistry are summed up in these twoideas, presented in the opening section:

1. Inorganic chemistry is a study of the propertiesof all the elements.

2. Each element is unique, yet it is possible toprovide a unifying description of all theelements.

You may wish to prepare an overhead trans-parency which duplicates the versions of Men-deleev's first periodic table that appear on page2 of the student module. This transparency canbe used in discussions of the introductory sec-tion and the first section, Periodicity: A ChemicalCalendar.

Periodicity: A Chemical Calendar

This section develops ideas about the periodicproperties of the elements. References to cyclicphenomena and everyday events help to clarifyperiodicity. Elements are classified first as metalsand nonmetals and later as families on the basisof recurring physical and chemical properties.Experiments reinforce family relationships. Even-tually the students move on to a miniexperimentin their investigation of periodic properties,especially ionization energies.

Mendeleev's contribution of the periodic tableis complemented by a discussion of his success-ful predictions of elements that were yet to be

discovered. The transition metals, as well as theposition of hydrogen in the periodic table, are dis-cussed with a reference to ionization energies.The concluding section considers the reactivityof the elements in terms of their positions in theperiodic table, valence electrons, and some simpletypes of compounds that may be formed.

A subtle emphasis on the importance of thetransition elements begins in the later parts ofthis section. Throughout the module the transi-tion elements continue to surface as a mostsignificant group of elements. The transition ele-ments enter into an investigation of enzymes,Lewis acids, coordination compounds, the struc-tures of metals, and, finally, the life processes.

1911

I -1 CHEMICAL CYCLES

Although the weekly cycle and the calendar arevalid counterparts of the periodicity of elementsand the periodic chart, the analogy in the modulediscussion may be limited by the fact that weeklycycles are somewhat less well defined than theyused to be. Different areas of our culture usedifferent cycles.

The introduction to the periodic chart here isclosely related to the film Chemical Families. Thefilm is a CHEM Study film, available for rentalor purchase from Modern Learning Aids.* Showthis film as an introduction to periodicity. It illus-trates experiments that are nearly impossible toreproduce in the high-school laboratory and pro-vides an interesting lead-in to periodicity.

1-2 ULTRAMAN VS. FLINTSTONES

In the discussion of the properties of metals andnonmetals (conductivity, luster, malleability, duc-tility) use actual samples to demonstrate theseproperties. For instance, hammer a piece of cop-per wire or foil or cut a piece of sodium.

The conductivity of heat by metals can be illus-trated by the fact that metals feel cool at roomtemperature. They are conducting heat away fromthe hand. On the other hand (pun intended!),when hot they feel even hotter for the same rea-son. Have you ever touched a hot pot lid insteadof the insulating knob?

If time permits, a discussion of properties ofmetals can be carried further. Most metals aresolids, the exception being mercury (gallium andcesium have low melting points, too, 29.8°C and28.5°C, respectively). Most metals are ratherdense, ranging from 0.53 g/cm3 for lithium to22.5 g/cm3 for osmium. Prompt your studentsto talk about metals with which they are familiar.Have them discuss the use of these metals ineveryday life.

The nonmetallic elements are less likely to beobserved in everyday activities. Many of theiruseful properties also happen to be exhibited bysome compounds. For example, sulfur could bemelted, cast in molds, and used as a nonconduct-ing insulator on high-voltage electrical lines, butso can glass, and the latter is stronger.

*Modern Learning Aids Division, Ward's Natural Science Establish-ment, Inc. P.O. Box 1712, Rochester, New York 14603.

12

1-3 PERIODIC PROPERTIES

In order to illustrate periodicity, properties thatare familiar to the student who has not studiedmuch chemistry were selected. However, the"best" properties to illustrate periodicity are to befound in the properties of the isolated atoms.Ionization energy is used in the present discus-sion, although it is less intuitively related tothe student's prior experience than the otherproperties.

Allow the students to investigate whether otherphysical properties of elements are periodic innature or not. The elemental values for theseproperties (melting point, density, etc.) may befound by the student in handbooks of chemistryand used in graphs similar to those on pages 10and 11 of the student module.

MINIEXPERIMENT1-4 PERIODICITY

This miniexperiment permits students to recognize aperiodic property through plotting ionization energy data.

Concepts In doing this miniexperiment, a student willencounter these important ideas:*

Ionization energy is a periodic property of chemicalelements.The basic repeating cycle of periodicity is that of eightelements.

Objectives After completing this miniexperiment, astudent should be able to:*

Defirie ionization energy.Graph ionization energy versus atomic number data.Determine the relationship between atomic numberand ionization energy in a chemical family and achemical period.

Estimated Time One period (45 minutes), includingthe discussion

Student Grouping Individuals

This statement appears only with this first miniexperiment, but itapplies each time this section appears in an experiment or mini-experiment, unless otherwise noted.

20

Materials You will need the following materials forclass of thirty students:*

30 sheets of linear graph paper15 pairs scissors1 roll of transparent tape (or glue)

Advance Preparation See Laboratory Tips.

a Notice that within each family of elements the ionizationenergy decreases as the atomic number increasesthat is, it decreases as one proceeds from top to bottom.(This rule is absolutely correct only for the representa-tive elements and some, but not all, transition-elementfamilies.)

The values of the ionization energies have been takenrelative to that of the ionization energy of hydrogen.Since the main point is to stress regularity and period-icity, it matters very little which units are used, and thereis no need to complicate things by using either kcal/moleor electron volts.

Pre lab Discussion The discussion of periodic trendsin sections 1-2 and 1 -3 leads naturally into this miniex-periment. Prepare a transparency for an overhead pro-jector that shows the graph axes. Or you might simplyput the graph axes on the chalkboard. Students maybenefit by reviewing section A-38 of Reactions andReason: An Introductory Chemistry Module.

Laboratory Tips The use of only the representativeelements presents some problems, since it requires thatthe atomic numbers jump from 10 to 31, 38 to 49, etc.(Note that the number 31 in the student's miniexperi-ment instructions is not a typographical error!) A refer-ence to only the representative elements also makesit necessary to postpone any discussion of more thanhalf the chemical elements. The alternative is to con-sider all the elements immediately, which leads to un-necessary complications. The addition of the transitionmetals and of the longer periods is discussed in sec-tion 1 -7.

Range of Results When the elements are arrangedaccording to the directions in the student module, thefollowing results can be seen: (1) elements with lowionization energies, such as sodium and potassium, arefound to the left of each cycle; and (2) the elementswith high ionization energies, such as fluorine andchlorine, are found to the right of each cycle. The logicalarrangement of elements based on this information formsa primitive sort of periodic table.

,Li

Na,,K

Rb55Cs

II

,Be

,,Mg

,0Ca

SrBa

III

,B

IV

,C

V

,N

PAs

VI

.0SSeTe

VII

9F

,,CI

BrI

VIII

,0Ne

,,Ar

KrXe

,,Al

3,Ga

In5,-11

I ,,Si

GeI.

,,,Sn

Pb,,Sb

Bi Po

.ncreaSIng 'alien energy

The Materials list for each experiment and miniexperiment in this moduleis planned for a class of 30 students working in pairs, unless other-wise noted. You may have to adjust this to fit the size of your class.

It generally takes a long time before students have anadequate "feel" for the concept of energy. It is highlyunlikely that they will feel comfortable with discussionsof energy at this stage of the game. Nevertheless, unlessone is to state authoritatively that "alkali metals loseelectrons and halogens gain them," some appeal mustbe made to the experimental evidence of ionizationenergies. The emphasis need not be strong, however.

One problem is that if the student has never stoppedto think about what is going on, the statement theionization energy is high, therefore the tendency to loseelectrons is low" or "the ionization energy is low, there-fore the tendency to lose electrons is high" may seemto be contradictory. An analogy of any inverse rela-tionship may help here. For example, the lower thetemperature, the more clothes you have to wear to becomfortable.

Post lab Discussion Have one student put his or herarranged data on the chalkboard as a basis for dis-cussion, or use an overhead transparency of thischopped-up, glued-together product. Emphasize theperiodicity of properties demonstrated by ionizationenergy. Point out the arrangement of elements intosimilar groups vertically and different groups horizontally.Do your students see the trends shown in the chart?

The importance of this miniexperiment and the postlabdiscussion is to point out the periodicity of the propertiesof elements and to show the trends. You may wish to.examine the periodic trends in other properties, such asatomic and ionic radii, electron affinity, etc. Althoughpolarity of chemical bonds has been discussed in Reac-tions and Reason: An Introductory Chemistry Module,the concept of electronegativity is not mentioned in thismodule until section 1-24. Nevertheless, you might wishto discuss it here in connection with ionization energies

2113

and electron affinities and show how electronegativityvaries periodically.

1-5 CHEMISTRY'S CRYSTAL BALL

The terms family and group have been used hereessentially interchangeably. The older terminol-ogy was to speak of Group I, for example, whichcontained both Family IA, or Subgroup IA (thealkali metals), and Family IB, or Subgroup IB(the coinage metals). It now appears that there islittle benefit to be gained by relating the A andB families to each other. About all these twofamilies have in common is a supposed +1 oxida-tion state, and it is the most stable only for Ag;Cu2+ and Au3+ are more stable than Cu+ and Au+.

For the same reason, not much is to be gainedbeyond a little chemical history by discussingMendeleev's "short form" of the periodic table.Mendeleev used it successfully to predict theproperties of both scandium (ekaboron) andgallium (ekaaluminum) and to distinguish theseelements (IIIB and IIIA) successfully, but he wasintimately familiar with the large differences andwhat are only formal similarities between the Aand B subgroups. For those beginning in chem-istry, the short form of the chart is apt to over-emphasize nonexistent similarities.

At this point you may wish to touch on theindependent discovery of the periodic law by theGerman chemist Lothar Meyer.* This is an oppor-tunity to remind students that the phenomenonof duplication of ideas and theories occurs fre-quently in science when enough events pointtoward a pattern and several independent work-ers make the same discovery. This process ofindependent discovery lends credence to thevalidity of scientific results and ideas. Interest-ingly enough, although their discoveries weremade independently, both Meyer and Mendeleevwere associated for a few years with the Univer-sity of Heidelberg, during a time of remarkablescientific activity there.

1-6 THE HYDROGEN AND HELIUM PUZZLE

Hydrogen and helium do not fit in with the restof the elements because they cannot form a stableoctet of electrons. Helium, however, shares allother properties of the noble gases: high'See A. J. Ihde, The Development of Modern Chemistry (New York:Harper & Row, 1964), pp. 249-251.

14

ionization energies, reluctance to form com-pounds, existence as atoms (rather than diatomicmolecules) in gases, etc. The difficulty with plac-ing hydrogen is that it is either an electron donoror acceptor (most often sharing an electron) andmay be variously placed according to the whimsof the chart-maker.

A possible way to conduct the discussion of thissection would be to use an overhead transparencyof a periodic chart with the spaces for hydrogenand helium omitted. You can then draw them inwith a marker or drop on an overlay with hydro-gen and helium on it. Let students suggest variouspossibilities of placement and try them out on theoverhead projector. Encourage the class to re-spond to them. Point out that because of itsionization energy, helium fits in very nicely withthe other elements in Group VIVA. Hydrogen,on the other hand, exhibits an ionization energytoo high to be placed in group IA and too lowto be placed in group VIIA.

2.00

1.80

>-1.60

P2 1.40ro

wc 1.20

1.00ro

.g 0.80

0.60

0.40

0.20

0.001 5 10 15 20 35 50 55

atomic number (Z)

noble gases

halogens

alkalimetals

Although it is common (and perfectly proper)to emphasize the difference between hydrogenand the elements of family IA (lithium, sodium,potassium, etc.) by the complete lack of metallicproperties of hydrogen, you should be aware thatscientists in this country and the Soviet Unionare trying to make "metallic hydrogen" by sub-jecting the gas to extremely high pressures.Theory predicts that hydrogen should becomemetallic at fantastically high pressure (millions ofatmospheres) [Science, 180:398 (27 April 1973)].

1-7 KEEPING UP WITH THE TRENDS

At this point, it is not necessary to delve into

22

the intricacies of the properties of transition met-als. The students should be aware that (1)transition metals exist; (2) they have both metallicand nonmetallic propertiesthat is, Cr and Mnact as metals by forming positive ions, but alsoas nonmetals by forming anions such as MnOand Cr2 02'; (3) they are placed in the peri-odic table between representative metals andnonmetals.

A discussion of transition-metal oxidationstates is presented later. The only reason transi-tion metals are discussed at all at this point isto show the student that the main trends of theperiodic chart remain the same if the transitionmetals are included.

The intricacies involved in the presence of delectrons in the transition metals (and of f elec-trons in the lanthanides and actinides) have beenglossed over here, as has the fact that a d1° con-figuration is a pseudo-noble gas configuration.This is in line with our philosophy expressed inboth Reactions and Reason: An Introductory Chem-istry Module and this module that detailed elec-tron configurations (s, p, d, f, etc.) do not promotea better understanding of chemistry at the high-school level, especially as usually encounteredin the "plug-them-in, crank-them-out" approachto electron configurations. This is especiallypronounced in the chemistry of the transitionmetals, where the stable oxidation states bearlittle resemblance to the ground state electronconfiguration. (Have you ever tried to explainto a student why Cr, . . . 3d 54s', forms a stableion, Cr3+, instead of Cr±? Or why are the 4selectrons lost first, even though according to theAufbau scheme they are not the last ones to beplaced?)

Miniexperiment By now, your students have hadsome exposure to the punning possibilities in chemistryand are acquainted with the names of many of theelements. You may wish to make an overhead trans-parency of the cartoon map on the following page.Show it to the class and ask the question, "Why arethere so many names like europium, americium, fran-cium, and germanium? Surely these are not just bitsof word play?"

If a student should ask about the origin of the namesof the elements, be prepared to relate some of these

names to their origins: Europium, discovered by aFrenchman, was named after, obviously, Europe. Theelements francium, germanium, and polonium (Poland)were named by the discoverers after their homelands.A similar name, but less obvious at first glance, isscandium (Scandinavia). Even more obscure, unlessyou are versed in the Latin language and ancient geog-raphy, are gallium (L. Gallia = France, approximately),rhenium (L. Rhenus, the Rhine), hafnium (L. Hafnia,Copenhagen), and ruthenium (L. Ruthenia, a provinceof Russia).

A discussion of these names can lead into the broaderdiscussion of the discovery of the elements and thesignificance of their assigned names. Some elementshave been named after cities (holmium, after Stock-holm); states (californium); people (mendelevium,curium, fermium, and einsteinium); the colors of theircompounds or the element itself: chromium (Gr. chroma,color), rhodium (Gr. rhodon, rose; cf. rhododendron),and chlorine (Gr. chloros, greenish-yellow). For thederivation of the names of the elements, see the Hand-book of Chemistry and Physics, Chemical Rubber Pub-lishing Company, Cleveland, Ohio. The Discovery ofthe Elements, by Mary Elvira Weeks and Henry M.Leicester, Chemical Education Publishing Company,Easton, Pennsylvania, gives interesting accounts ofhow the elements were discovered and named.

1-8 FAMILY RELATIONSHIPS

It is difficult to choose good examples for thissection. Almost all of the properties of the ele-ments reflect their periodic nature in one way oranother, but sometimes the periodicity tends tobecome obscured. (To extend the previous anal-ogy, there are some times of the year, on vaca-tion trips, for example, when the days of the weektend to become less important.)

There are few good chemical examples that maybe offered to the student without the addition ofmany qualifications, explanations, or extensivediscussions. For example, in Chemical Families,the film mentioned previously, hydrogen is sep-arated from the halogens (X2) on the basis of twoproperties:

NaH + H2O 0 NaOH + 1-12NaX + H2O + no reaction (just dissolves)

and

23

P4 + H2 no reactionP4 + X2 P2 X4, PX,, and PX,

15

TH

ES

CA

ND

IUM

CO

UN

TR

IES

PO

LON

IUM

GE

RM

AN

IUM

The first distinction is a very good onethehydride ion is considerably different in its prop-erties from the halide ions. The second distinctionis somewhat artificial, however, since, althoughit correctly distinguishes hydrogen from thehalogens, it has been carefully chosen to illustratethe desired difference in properties. First, phos-phorus does form compounds with hydrogen,although they cannot be prepared by direct syn-thesis from the elements. Secondly, if, in placeof phosphorus, sulfur had been chosen as a"typical" nonmetal, it would have been foundthat hydrogen reacts with sulfur (at 600°C), asdo fluorine, chlorine, and bromine, but that iodinedoes not react. Using this reaction as a criterion,hydrogen, fluorine, chlorine, and bromine wouldform a natural family, and iodine would bedifferent!

This is not meant to indicate that there is any-thing abnormal about sulfur (or iodine) or thatthe periodic properties of the elements are notoverwhelmingly well-documented. It is simply amatter of fact that in most cases the periodicityof chemical properties is based on a large numberof reactions and properties, most of which aredetermined by several factors that tend to addand subtract in their effect. These factors (atomicsize, electronegativity, availability of d orbitals,etc.) are, in general, too involved to bring intoan elementary discussion.

The lanthanide and actinide elements havebeen given short shrift, beyond an explanationof where these blocks of elements are located.There is sufficient material of more immediateinterest that must be included rather than affordthe lanthanides and actinides special coverage.

For advanced or able students, it may be de-sirable to go more deeply into the periodicity ofthe elements. A nice comparison can be madebetween the actinides and lanthanides. Until 1944the elements thorium, protactinium, and uraniumwere considered to be congeners of hafnium,tantalum, and tungsten. The first attempts tomake the element number 93 (later to be namedneptunium) were predicated on its supposedsimilarity to rhenium. The attempts failed. It wasabout this time that the eminent American chem-ist Glenn Seaborg suggested that these elementsconstituted a second inner transition series, anal-ogous to the lanthanides. The Manhattan Project

25

during World War II thus spent a great deal oftime and money elucidating the properties of thelanthanides, as well as the synthetically producedactinides. For a more nearly complete discussionof this problem, see G. T. Seaborg, Man-MadeTransuranium Elements (Englewood Cliffs, N.J.:Prentice-Hall, 1963), chapter 3.

A second topic that might be of interest tostudents who are already somewhat familiar withthe periodic chart is the current interest in syn-thesizing new elements. The actinide series wascompleted with element number 103, lawren-cium. The two succeeding elements, rutherfor-dium and hahnium, numbers 104 and 105, are truecongeners of hafnium and tantalum. There areexciting possibilities for forming elements in theregion of element number 114 and perhaps evenhigher. See The Heart of Matter: A Nuclear Chem-istry Module and G. T. Seaborg, "Prospects forFurther Considerable Extension of the PeriodicTable," Journal of Chemical Education (October1969), pages 626-634.

Note that there is currently some controversyover the discovery of these heavy elements, andboth the American group at Berkeley and theRussian group at Dubna have proposed namesbased on the right of prior discovery. The equiva-lents are:

Atomic Number102103104105106

American Namenobeliumlawrenciumrutherfordiumhahnium

Russian Namejoliotium"103"kurchatoviumnielsbohrium

*As yet no name has been proposed.

For your own information concerning some ofthe "details" of the periodic chart (please don't tryto introduce all the ideas to your students), youmay be interested in reading "Anomalous Prop-erties of Elements That Follow 'Long Periods' ofElements," by J. E. Huheey and C. L. Huheey,Journal of Chemical Education (April 1972), pages227-230.

It is interesting to note that phosphorus wasthe earliest element to be "discovered" that is,to be found by experimentation and not justknown as common knowledge from the ancients.

17

It was discovered by Brand in 1669.* In contrast,the first artificially prepared element was tech-netium, created by the bombardment of molyb-denum with neutrons and announced by Perrierand Segre in 1937. The last blank within theperiodic chart (this does not include the trans-lawrencium elements, which go on indefinitely)was filled in 1945 by the artificial production ofpromethium by Marinsky and Glendenin. ThePeriodic Table of the Elements on the following pagegives some idea of the dates of discovery of theelements (see also the figure on page 34 of Reac-tions and Reason: An Introductory Chemistry Modulefor additional information).

MINIEXPERIMENT1-9 ALL IN THE FAMILY

A demonstration of the periodic trends in chemicalreactivity would require a sophisticated setup such asthat used in the film Chemical Families. Some reactions,however, are rather simple and well within the realmof possibility for most high-school laboratories. Thisexperiment is an example.

Concepts

There are observable trends in the reactivities ofelements in a given family.Halogens with greater oxidizing ability will displaceother halide ions.

Objective

Determine relative chemical reactivity of the halogensthrough redox reactions.

Estimated Time One-half period

Student-grouping Pairs

Materials

200 cm3 TTE, trichlorotrifluoroethane (Freon 113 orDu Pont TF Solvent)

50 cm3 chlorine water50 cm3 bromine water50 cm3 iodine solution50 cm3 0.1 M KCI

*See M. E. Weeks and H. M. Leicester, Discovery of the Elements,7th ed. (Easton, Pa: Chemical Education Publishing Company, 1968).

18

50 cm3 0.1 M KBr50 cm3 0.1 M KI90 18 x 150-mm test tubes90 test-tube corks15 test-tube racks15 10-cm3 graduated cylinders

Advance Preparation Chlorine Water For conve-nience, commercial bleach, such as Clorox and Purex,acidified with concentrated HCI (4-6 drops concentratedHCl per 100 cm3 bleach) can be labeled as "chlorinewater" and used in the experiment. Chlorine water maybe used, if you have it, or it may be prepared by bubblingchlorine gas into a flask containing distilled water. Cau-tion: CI, is poisonous. This operation should be con-ducted under a hood in a well-ventilated room. If atank of Cl2 is not available, chlorine may be generatedby the oxidation of HCI (see illustration); 10 g MnO2and 40 cm3 concentrated HCI will generate sufficientC12. Heat the reaction vessel gently. Cl2 will be col-lected in the cold water bottle.

Optional setup for generation of chlorine gas

26

PE

RIO

DIC

TA

BLE

OF

TH

E E

LEM

EN

TS

IAIIA

6.94

LiLi

thiu

m3

9.01

Be

Ber

ylliu

m4

23.0 N

aS

odiu

m11

24.3 M

gM

agne

sium

12III

B

1.00

8 HH

ydro

gen

1

200.

6 __

-ato

mic

mas

s/s

ymbo

lM

ercu

ry-n

ame

80-

atom

ic n

umbe

r

IVB

VB

VIB

VIIB

VIII

BIB

IIB

IIIA

IVA

VA

VIA

VIIA

VIII

A4.

00 He

Hel

ium

2

10.8 B

Bor

on5 27

.0 Al

Alu

min

um13

12.0 C

Car

bon

6 28.1 S

iS

ilico

n14

14.0 N

Nitr

ogen

7 31.0 P

Pho

spho

rus

15

16.0 0

Oxy

gen

8

19.0 F

Flu

orin

e9

32.1 S

Sul

fur

16

35,5 C

IC

hlor

ine

17

20.2 N

eN

eon

10 39.9 A

rA

rgon

18

39.1 K

Pot

assi

um19

40.1 C

aC

alci

um20

45.0 S

cS

cand

ium

21

47.9 T

iT

itani

um22

50.9 V

Van

adiu

m

23

52.0 C

rC

hrom

ium

24

54.9 M

nM

anga

nese

25

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kel

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r29

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30

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.

Bromine WaterIf bromine water as such is not avail-able, dissolve 4 grams KBr in 50 cm3 chlorine water orcommercial bleach (Clorox or Purex) and label this as"bromine water." If elemental bromine is available, pourthe bromine into a flask containing distilled water, stir,let settle, and decant bromine water. The excess Br2will simply settle to the bottom. Fresh bromine watercan then be prepared by adding more water to the flask.

Iodine SolutionThe iodine solution (I, in KI reagent)may be prepared by dissolving 1 g KI in distilled water,adding 0.5 g 12, and diluting to 50 cm3.

To prepare 0.1 M KCI, dissolve 0.4 g in 50 cm3 water.

To prepare 0.1 M KBr, dissolve 0.6 g KBr in 50 cm3water.

To prepare 0.1 M KI, dissolve 0.8 g KI in 50 cm3 water.

Pre lab Discussion See section 1-8.

Laboratory Tips To facilitate handling of the chem-icals, place solutions in small bottles and use medicinedroppers to disperse. Caution: The halogen solutionsare corrosive and should be flushed away with waterimmediately if they come in contact with the skin.

Post lab Discussion On the basis of their observa-tions, students should complete and balance the equa-tions in the test:

2KBr + Cl2 0 2KCI + Br22KI + C12 --o 2KCI + 12KCI + Br2 N.R.2KI + Br2 --o 2KBr + 12KCI + 12 o N.R.KBr + 12 p N.R.

In discussing the "missing element," fluorine, let yourstudents come to the realization that since F2 would beat the top, it would react with all the other halides. Inaddition, manufacturing F2 requires special methods andit is so reactive that it is a dangerous chemical to havein the laboratory.

The students may also inquire into the absence ofastatine. This element is very rare and radioactive.Studies indicate that it behaves as expected and isless reactive than iodine.

1-10 GAINERS AND LOSERS

The point to stress here is the stable octet of elec-trons possessed by the Group VIIIA elements.

20

The halogens, Group VIIA, have one electronmissing from their octet and therefore tend toaccept electrons:

X + e-

The alkali metals have an electron beyond thestable octet and tend to lose that electron:

m +e-

In contrast to section 1-8, where we consideredtrends within families, here the emphasis is ondifferences between families.

The students may benefit by using a worksheetfor writing formulas of binary compounds. Keepthe majority of examples brief and similar to theexamples in the module.

Your students may benefit from a discussion ofthe periodic table as arranged by Glenn T. Sea-borg. If you wish, prepare a transparency of theperiodic table illustrated on the following pagefor use on the overhead projector. This duplicatesthe smaller version in the student module.

You may wish to use this table in conjunctionwith the Mendeleev tables and the present-dayperiodic table as a review of this section.

ANSWERS TO PROBLEMS

(Student module page 24)

1. (CI, Br, I); (Ca, Sr, Ra); (Cu, Ag, Au)

2. CI, Br, and I have similar properties and form similarcompounds, as seen in 1-9 and 1-10. Cu, Ag, andAu are all metals and have all been used to makecoins; in fact, the group is known as the "coinagemetals." Ca is a major component of the structureof bone. Both radioactive strontium (90Sr) and radium(226Ra) can cause bone disease, the former fromradioactive fallout and the latter from a form of radiumpoisoning exemplified in the notorious case of womenwho worked in factories painting luminous watch dials.

3. Al, Ga, In

4. Cs, Mo, Ca, K, Fe, and Ni are metals; C, S, N, I, B,P, and Ne are nonmetals.

5. 2KBr + Cl2 0 2KCI + Br22KI + Br2 0 2KBr + 122KCI + F2 -0 2KF + Cl2

8

PE

RIO

DIC

TA

BLE

SH

OW

ING

HE

AV

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LEM

EN

TS

AS

ME

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IES

AR

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NG

EM

EN

T B

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LEN

N T

. SE

AB

OR

G

1945

1 H1.

00

1 H 1.00

8

2

He

4.00

3

4 Be

9.02

5 B 10.8

2

6 C 12.0

10

7 N 14.0

08

8 0 16.0

00

9 F 19.0

0

10 Ne

20.1

83

3 Li 6.94

0

12

Mg

24.3

2

13 Al

26.9

7

13 Al

26.9

7

14 Si

28.0

6

15 P 30.9

8

16 S 32.0

6

17 CI

35.4

57

18 A 39.9

44

11 Na

22.9

97

19 K39

.096

20 Co

40.0

8

21 Sc

43.1

0

22 Ti

47.9

0

23 V50

.95

24 Cr

52.0

1

25 Mn

54.9

3

26 Fe

55.8

5

27 Co

58.9

4

28 Ni

58.6

9

29 Cu

6337

30 Zn

65.3

8

31 Ga

69.7

2

32 Ge

72.6

0

33 As

74.9

1

34 Se

78.9

6

35 Br

79.9

16

36 Kr

83.7

37 Rb

85.4

8

38 Sr

87.6

3

39 Y88

.92

- 40 Zr

91.2

2

41 Cb

92.9

1

42 Mo

95.9

5

4344 Ru

101.

7

45 Rh

102.

91

46 Pd

106.

7

47 Ag

107.

880

48 Cd

112.

41

49 In11

4.76

50 Sn

118.

70

51 Sb

121.

76

52 Te

127.

61

53 I

126.

92

54 Xe

131.

3

55 Cs

132.

91

56 B a

137.

36

57 L. 38.9

2

58-7

1

si.:

6616

72 Hf

178.

6

73 To

180.

88

74 W 183.

92

75 Re

186.

31

76 Os

190.

2

77 Ir19

3.1

78 Pt

195.

23

79 Au

197.

2

80 Hg

200.

61

81 TI

204.

39

82 Pb

207.

21

83 Bi

209.

00

84 Po

8586 Rn

222

8788 Ra

89 ..Se

e4e

SOII

16

90 Th

91 Pa

92 U93 Np

94 Pu

9596

LAN

TH

AN

IDE

SE

RIE

S

AC

TIN

IDE

SE

RIE

S

57 La 138.

92

5859

6061

6263

6465

6667

6869

7071

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu14

0.13

140.

9214

4.27

150.

4315

2.0

156.

915

9.2

162.

4616

3.5

167.

216

9.4

173.

0417

4.99

89 Ac

90 Th

232.

12

91 Pa

231

92 U23

8.07

93 Np

237

94 Pu

9596

EVALUATION ITEMS

These are evaluation items that you may wish to usewith your students at various times during the precedingsection. The correct answer to each question is indicatedby shading.

1. Metallic elements are normally

A. good conductors of electricity and malleable.B. good conductors of electricity and brittle.C. poor conductors of electricity and malleable.D. poor conductors of electricity and brittle.

2. As one moves along a given row in the periodictable, ionization energy

A.

B.

C.

D.

decreases from left to right.increases from left to right.remains unchanged.increases, then decreases.

3. Which of the following diagrams best represents therelationship between ionization energy and atomicnumber?

1.

IE

A. 1 B. 2 C. 3 D. 4

Z

2. 4.

IE

Z

22

IE

Z

z-4

4. Which of the following explanations is best for notplacing hydrogen in either group IA (alkali metals)or group VIIA (halogens)?

A. Hydrogen is a much lighter element than thealkali metals or the halogens.

B. Hydrogen can form compounds with all otherelements.

C. The ionization energy of hydrogen is too high forgroup IA, but too low for group VIIA.

D. None of the above

5. Which of the following statements is true?

A. Transition metals are poor conductors of elec-tricity.

B. Transition metals are found between the GroupIIA metals and the Group IIIA metals and non-metals.

C. Transition metals do not exhibit periodicity in theirchemical and physical properties.

D. Transition metals do not exhibit both metallic andnonmetallic properties.

6. The most chemically active of the elements I, Cu,He, and F is:

A. I

B. CuC. HeD. F

7. The least chemically active of the elements F, CI, Br,and I is:

A. FB. CI

C. BrD. I

8. Which element has the greatest tendency to loseelectrons?

A. FrB. F

C. SD. Be

9. Which of the following would be a correct formulafor a compound between H and F?

A. H2FB. HF2

C. H2F,D. None of the above

30

Structural Chemistry of Metalsand Their Compounds

By now students are aware of the chemist's reli-ance upon an understanding of periodic prop-erties. Here the properties of metals are explainedin relation to their lattice structures. Why metalsuseful in construction are largely members of thetransition elements is explained by analogy, usingmodels of their lattice structures. Coordinationnumbers, packing efficiencies, and types of latticestructures are discussed and studied throughexperiments.

A similar study is made of some representa-tive ionic compounds. Opportunities to contrastthe properties of metallic and ionic solids areprovided by considering the nature of their latticestructures as well as electrical charge or absenceof charge. (For instance, why are metals malleableand ionic crystals brittle?)

1-11 WHY ARE METALS "METALLIC"?

In some ways, metals are very simple materials.Elemental metals such as gold are composed ofonly one type of atom, and their geometry (asbecomes apparent in the following sections) isrestricted to a few simple types. On the otherhand, the bonding in metals is difficult to describein simple, nonquantum-mechanical terms. In thissection, a short introduction to the problem isstated with a provisional explanation of the bond-ing: The metallic bond resembles Ping-Pong ballsheld together by molassesthat is, strong attrac-tive forces ("stickiness"), but there is freedomfor the atoms to move past each other (metalsare malleable), and the electrons ("molasses")can flow as well (electric current). These prop-erties are discussed in more detail later, so do notfeel compelled to go into the subject at greatlength now. The section is meant to be exactlywhat its title impliesa question. As the studentsperform the experiments and miniexperiments,facts will be learned. They will develop theoriesthat will reinforce an understanding of metals.

MINIEXPERIMENT1-12 WHO'S WHO?

The purpose of this miniexperiment is to acquaint thestudent with some of the important properties of metals

31.

and nonmetals and to use these properties to classifyelements into the two groups.

Concepts

Metals have characteristic and distinctive properties.Nonmetals have characteristic and distinctiveproperties.

Objective

Classify elements as metals and nonmetals on thebasis of their physical properties.


Student Grouping Pairs

Materials

15 10-cm lengths of:copper wirealuminum wirelead wirezinc wiretungsten wiremolybdenum wire

Note: Many metals in the form of wire (lead and tungsten,for example) may be purchased from Research Organic/Inorganic Chemical Corporation, 11686 Sheldon Street,Sun Valley, California 91352, or from Alfa Division,Ventron Corporation, P.O. Box 299, Danvers, Mas-sachusetts 01923.

You will also need:10 g sodium5 g lithium5 g graphite (pencil lead)5 g iodine50 g sulfur (lump)conductivity apparatus (1.5 volt D cell, 1.5 volt bulb,

alligator clips, wire, miniature socket)

Best results will be obtained by using wires of com-parable diameter. If a stock of wires is not available, usepieces of metal of similar dimension. Copper and zincsheets are often in laboratory stock. Brass shim stockmay be obtained from the school shop, lead fromplumber's wool, and tungsten from light-bulb filaments.

There are only a few nonmetals that are solids whichcan be used for comparison. Lump sulfur (not flowersof sulfur) is good, and iodine can be used if students

23

are warned that it is corrosive. Graphite from lead formechanical pencils is suitable, although it is an excep-tional nonmetal that does conduct electricity. Whitephosphorus could be used in a teacher demonstra-tion, but it is too flammable and poisonous for studentuse.

Advance Preparation See Materials

Pre lab Discussion We have purposely left the in-structions to the students somewhat nonspecific to al-low the teacher some flexibility in choosing materialsand tests to be performed. Call to your students' atten-tion the materials that you have selected for testing.Suggest to your students that they test the materialsfor (1) physical appearance, (2) electrical conductivity,and (3) malleability and ductility.

Students can test for physical appearance by observingproperties such as color, luster, texture, and shape. Totest conductivity, you can set up a simple conductivityapparatus. All you will need is a dry cell, a miniaturesocket, a flashlight bulb, bell wire, and alligator clips.You can test for malleability and ductility by drawingwires, bending metals, and hammering metals.

Laboratory Tips You might get the class started byconducting some demonstrations. For example, you caneasily demonstrate the low melting point (70°C) ofWood's Metal (50 percent bismuth, 25 percent lead,12.5 percent tin, 12.5 percent cadmium). Teaspoonsmolded from Wood's Metal melt when used for stirringhot tea. You can demonstrate the physical propertiesof sodium (luster, malleability, conductivity, relativesoftness) by cutting a chunk with a knife to expose afresh surface. Note that the luster quickly fades whena film of oxide forms as a result of contact with the air.

Range of Results The greater the number of samplesyour class works with, the greater is the number of prop-erties the students will observe. Suggest to your studentsthat they each compile a list of the properties that theirtests reveal. Have students compare their lists. In allprobability, the lists will vary. If conflicting conclusionsarise, have the students retest the material that is inquestion.

Post lab Discussion Have your students go over thelists of properties that they have compiled. Then compilea general list from the students' individual lists. Put this

24

list on the chalkboard. Call upon a student to enumeratesome differences between metals and nonmetals. Inviteothers in the class to comment on the student's enumera-tion and, if necessary, to add to his or her list. Whichmaterials are metals? Which materials are nonmetals?Discuss. Form conclusions.

1-13 HOW'S YOUR COORDINATION?

A brief introduction to the concepts of coordina-tion number and efficiency of packing can serveas a prelab discussion to the following experi-ment, 1-14. However, it may prove more inter-esting to plunge right into the experiment anddiscuss both concepts as the need arises.

EXPERIMENT1-14 BECOMING AN EFFICIENCY EXPERT

The purpose of this experiment is to acquaint the stu-dent with the relationship between coordination numbersof different lattices and their efficiency of packing.

There are no "right" or "wrong" ways to arrange theballs, only different ways, some more efficient than oth-ers. The plastic boxes define the boundaries withinwhich the student will "pack" atoms. Plastic boxes asdescribed are recommended for use in this experiment,since substitutes do not have appropriate dimensions.

Although we feel strongly that there is no substitute for"hands on" experience by the studentsbuilding mod-els, trying various possibilities, and getting results thatcan be discussed and even debatedcertainly it is alsovery useful to have prebuilt models available for use.The advantages of prebuilt models include accuracy,stability (nothing is as exasperating as having a structure"collapse" at a critical point in a discussion), clarity,and versatility. They need not be expensive models;models quite suitable for use in your classes can readilybe constructed from Styrofoam balls similar to thoseused in this experiment. Construction of demonstrationmodels can be an interesting special project for someof your students.

Concepts

The coordination number of an atom in a latticeis determined by counting the number of nearestneighbors.

32

Different lattice structures may have different coor-dination numbers.Some lattice structures have greater packing ef-ficiency.

Objectives

Determine the coordination number of lattice struc-tures.Construct three-dimensional metallic lattices, usingplastic balls and boxes as models.Calculate the packing efficiency of a lattice structure.

Estimated Time One and one-half periods


Materials

15 plastic boxes15 false bottoms15 sets of Styrofoam or polystyrene balls, 1" (2.54 cm)

diameter (150 to 200 balls in a set)84 polystyrene balls, 5 cm to 8 cm in diameter (optional)

Enough copies of a worksheet for this experiment maybe duplicated ahead of time (see following page).

Note: You can make the plastic boxes out of 1/8" Plexi-glas sheets,* 4' x 6' in size. Such sheets can bepurchased from any Plexiglas dealer. Styrofoam andpolystyrene balls are available from Edmund ScientificCompany, 801 Edscorp Building, Barrington, New Jersey08007, or from Science Related Materials, P.O. Box1442, Janesville, Wisconsin 53345. Science RelatedMaterials also offers cork balls and precolored poly-styrene balls, but they are more expensive.

*Although we are firmly committed to the metrication of America, westill have a long way to go. Any teacher who goes into the school shopand asks for a 102 x 152-mm box made of 3.175-mm thick Plexiglasis probably asking for trouble. Therefore all dimensions are givenin inches.

7/8"

57/8"_)1 k -HA---

false bottom

8

bottom piece

8"

Advance Preparation The plastic boxes are con-structed of clear acrylic material (Plexiglas), 6" x 8"(inside dimensions of base) and about 3" high. Usemethylene chloride solvent to glue the pieces of plastictogether. The false bottoms are single pieces, 57/8" x77/8". For the body-centered cubic (BCC) packing ac-tivity, you can use strips that measure 57/s" x 21/2"(approximately). Instructions for the use of these stripsare discussed in the Laboratory Section. These dimen-sions are for the 1/8" thick Plexiglas. If other thick-nesses are employed, the dimensions of the end piecesand side pieces should be adjusted accordingly. Theplastic sheet can be cut by using a Plexiglas cutteror saw.

Wet the edges of the pieces with methylene chloride.Apply the methylene chloride at the joint with a syringeor a medicine dropper, with the tip drawn to form acapillary tip. Methylene chloride dries rather quickly, andit therefore will not be necessary to hold the pieces fortoo long. No clamps will be needed. After gluing theside pieces, add the end pieces in the same manner.Glue the end pieces to the edges of the bottom pieceand the side pieces.

Give each pair or group of students a set of plasticballs of Styrofoam or expanded polystyrene, 1" in

diameter and all of one color (150 to 200 balls in a set).Half of the student groups can work with white ballsand half with colored balls. You can color the balls bydipping them in latex paint. Spray paints can also beused, but difficulties sometimes arise as a result of thesoftening effect of spray paints. We prefer the harderand slicker expanded polystyrene balls over the rough-surfaced Styrofoam.

You will need the following transparencies:

Square lattice (transparency 1)Hexagonal lattice (transparency 2)

side pieces

33

T3"

L

61/ ".

end pieces

21/2"

57/s"

strips

25

26

WorksheetExperiment 1 -14

1. Calculation of the volume of a single atom:A (diameter of atom) x 1/2 =

B. (radius) 3 (r3)

C. (r3) x 1.333 x 3.1416 (pi) =

(radius)

(volume of each atom)

2. The simple cubic lattice structure:A. (no. of atoms) x (vol. of each atom) =B (W) x (L) x (H) = (vol. of box)

Efficiency = Volume of atoms (2A)Volume of lattice (2B)

3. The face-centered cubic lattice (FCC) structure:A (no. of atoms) x (vol. of each atom) =B (W) x (L) x (H) = (vol. of box)

Efficiency =(3A)(3B)

The coordination number of this structure is

4. The body-centered cubic lattice (BCC) structure: (optional)A (no. of atoms) x (vol. of each atom) =B (W) x (L) x (H) = (vol. of box)

Efficiency = (4A)(4B)


5. The hexagonal, closest-packed lattice (HCP) structure:A. (no. of atoms) x (vol. of each atom) =B. (W) x (L) x (H) = (vol. of box)

Efficiency = (5A)(5B)


6. The cubic closest-packed (CCP) structure:A. (no. of atoms) x (vol. of each atom) =B. (W) x (L) x (H) = (vol. of box)

Efficiency = (6A)


34

Second layer of hexagonal closest-packing and cubicclosest-packing (transparency 3, preferably of anothercolor)

Third layer of hexagonal closest-packing (transparency2; second copy), where circles are marked with felt-tip pen

Third layer of cubic closest-packing (transparency 4),colored differently

Bottom layer of body-centered cubic (transparency 5)Second layer of body-centered cubic (transparency 6)

Models for these transparencies can be found on thefollowing pages. Given the extra work involved in mak-ing transparencies 5 and 6, the models provided aredrawn to actual size. Each transparency should be adifferent color, either made from colored plastic ormarked with a felt-tip pen.

Pre lab Discussion Explain the general purpose ofthe experiment. (The purpose is to establish the dif-ferent ways that atoms can be arranged in a crystalstructure.) Try to avoid giving the impression that thereis a "right" way to do it. Encourage individuality. Theexperiment is most successful if half the class gets onearrangement and half gets another.

Laboratory Tips A suggested way of conducting thisexperiment would be to have an overhead projector setup with all the transparencies of the different arrays al-ready prepared and ready to be used.

Have the students measure the dimensions and cal-culate the efficiency of each lattice as it is built. As aparticular structure is completed, you might project thestructure on the overhead projector as a transparency,by placing a transparent box directly on the overheadprojector, or by using transparencies 1 and 2. Brieflydiscuss the structures and their differences as they arecompleted. After different structures have been tried,ask all of the students to make a square array as thebottom layer in their boxes. Then ask them to add twomore layers in any way they choose. If the second layeris identical and congruent with the first, your studentshave constructed a simple cubic lattice with C.N. of 6.If the second layer is a square lattice, but displacedso that the atoms lie in the "pocket" between four atomsof the first layer, they have constructed a face-centeredcubic lattice with C.N. of 12.

Here, as well as later in the module (page 37), the stu-dents are working with two-dimensional arrays beforeproceeding to three-dimensional lattices. If any of your

35

students object that the "real world" is three-dimensionaland that working in two dimensions is a waste of time,you might refer them to an article that discusses mono-layers of adsorbed materials as two-dimensional solids,liquids, and gases! See J. C. Dash, "Two-DimensionalMatter," Scientific American (April 1973), pages 30-40.

Body-Centered Cubic (Optional). This lattice is almostimpossible to make without a fixed starting layer, sincethe atoms are not tangent in the square layers in thebox. Place a copy of the array in transparency 5 in thebottom of a plastic box and place a false bottom over it.Now glue 35 balls over the marked spots. A BCC arraydoes not fit exactly into a 6" x 8" box. To increasethe accuracy of the model, a 21/2" x 57/8" strip can beglued to the false bottom over the dotted lines. The ballsshould be tangent to the box on all sides now. Havethe students make a BCC lattice or, (if only one BCCarray is available) make it for them. To project animage of the body-centered cubic lattice, place trans-parency 5 on the projector stage, and then drop trans-parency 6 over 5 as an overlay.

TRANSPARENCY 5

00000000000 0 0 0 000000000000000000000

5 WITH 6 AS OVERLAY

TRANSPARENCY 6

000000000000000000 0 00000

27

TRANSPARENCY 1square latticer

L

TRANSPARENCY 32nd layer of HCP and CCP

28

TRANSPARENCY 2hexagonal lattice

TRANSPARENCY 43rd layer of CCP

3

TRANSPARENCY 5bottom layer of BCC

Ii

II

II

II

II10 0 0 0 Cit

C

'000 0 0 0 C

110 0 0 0 C00 0 0

37

TRANSPARENCY 62nd layer of BCC

O 0000000O 000O 0000000O 00

38

Next ask the students to make a hexagonal array inthe bottom layer of their boxes. Ask them to add twolayers in any way they choose.

A. Hexagonal closest-packed lattice, second layer in"pockets" between three atoms of first layer, thirdlayer directly over the atoms in the first, (C.N. = 12).Called an AB, AB, AB structure. You may show asecond copy of transparency 2 on top of trans-parencies 3 and 2. Notice that there are still "holes"in the array.

B. Cubic closest-packed lattice, second layer as in HCP,third not directly above first layer (there is only oneway to do this). (C.N. = 12). Called an ABC, ABCstructure. Show transparency 4 on top of trans-parencies 3 and 2.

(1) (2)

A

A

Arrangement of layers (1) AB, AB, AB in hexagonal closest-packed structure and (2) ABC, ABC in cubic closest-packedstructure.

A note in the Journal of Chemical Education 49 (1972),page 674, suggests a method of using the overheadprojector to help the students see the difference betweenHCP and CCP.

The determination of the coordination number shouldoffer no special problem. In calculating efficiencies,however, point out to the student the need to isolate,at least mentally, a "unit" cell, in which case one mustconsider the volume occupied by fractions of balls. Tohelp the student with this you may build a "unit cell" for asimple structure like the simple cubic. Obtain a largeStyrofoam ball and slice it in such a way that you geteight octants.

Then turn the octants around and connect them withtoothpicks in such a way that a cube is formed.

This makes evident the fact that only eight 1/8 balls or onefull ball occupy any space in the unit cell of side 2r.

Hence the efficiency in this case is

Efficiency(8)(1/(2r)3 7Tr3) x 100% = 52.3%

Range of Results The expected values for the dif-ferent structures are

Lattice Type

simple cubicface-centered cubicbody-centered cubichexagonal closest-packedcubic closest-packed

CoordinationNumber Efficiency

6 52%12 74%

8 68%12 74%12 74%

Although most of the students should be able to ob-tain the correct coordination numbers, the calculatedefficiencies (with the exception of the simple cubic) willgenerally be lower. A calculated value higher than thoselisted above will probably be the result of a gross errorin counting the balls or in the calculations. The low valuesresult from not including the fractions of balls that wouldfit near the edges of some of the layers.

Post lab Discussion Use the results obtained by thestudents as reported in the worksheets. You may alsopoint out that, although it was not brought out in theabove discussion (purposefully, though mentioned onpage 31 of the module), the face-centered cubic struc-ture and the cubic closest-packed structure are identical.They differ only in the way they are viewed. This in-teresting point can be brought out by a pyramid of close-packed atoms that has been dubbed the "Pau lingPyramid."

39 31

Using 84 polystyrene balls 5 cm to 8 cm in diameter, con-struct the Pau ling Pyramid as illustrated in the figuresbelow. For the purpose of clarity, eight of the balls shouldbe a different color, as indicated by the shaded balls.

PAULING PYRAMID

bottom or first layer

Key:

corner of FCC unit, must be colored

optionally colored

atoms glued together

The base of the pyramid can be held in place by a racklike that used to arrange billiard balls. A more con-venient method is to assemble sets of three balls gluedtogether (shown by connecting lines in the diagram).These triangular sets form a solid base and also helphold in the upper layers. Construct the layers as shownin the diagram. The corners of an FCC unit cell aredesignated by the colored atoms. By carefully removingthe other atoms, you can remove this unit cell in onepiece. It should look like the figure in the top marginon page 34 of the student module.

32

second layer

third layer

fourth layer fifth layer

0000 000

sixth layer

40

top atom

Ask the class what type of packing is exhibited by thepyramid. Slowly dissect the pyramid, layer by layer, toreveal that the apical atom in the center does not repeatuntil three layers have been removed, hence an ABCstructure, or cubic closest-packing. Continue to dissectuntil the unit cell is exposed. Remove it and show itsresemblance to the figure in the top margin on page34 of the student module.

The students will more readily see the identity if youhave previously shown them a Styrofoam model of anFCC unit cell.

1-15 METALLIC PROPERTIES: LOOK AGAIN

There are only three common lattices for metalatoms in the solid state: body-centered cubic,face-centered cubic (or cubic closest-packed), andhexagonal closest-packed.

FCC (CCP) HCP BCC

Ca Fe Cu Be Ti Li CaSr Co Ag Mg Hf Na SrSc Ni Au Ca Zr K BaLa Rh Sr Mo Rb

Ir Sc Co CsPd Y Ni

Pt La

Ti CrZr MoHf WV FeNb U

Ta

Note that HCP structures have an easy glide plane(see page 34 of student module). CCP lattices haveeven easier glide planes (though we felt theywere less easily illustrated). Some of the mostmalleable metals are Ag and Au (CCP and onlyone valence electron = "thin molasses"). HCPmetals are also usually malleable, except formetals such as Cr, Mo, and W (6 valence elec-trons = "thick molassess"). BCC lattices have dif-ficult glide planes and tend to be hard. Exceptionsare the Group IA and Group IIA metals (1, 2 elec-trons = "thin molasses"). Note that some metalscrystallize in more than one lattice. As expected,for example, CCP-iron is softer than BCC-iron.

All of the above is based on an "ideal" crystal.Some crystal defects that occur are:

1. Vacanciesa lattice point is unoccupied.2. Interstitialsatoms occupy positions between

lattice points.

41

3. Dislocationsone layer may be incomplete,causing a shift or tilt in the next layer of atoms.

4. Chemical defectsa foreign atom (impurity)is incorporated into the lattice.

The presence of defects can be either good or bad,depending upon the properties that we desirein the metal. Metals often decrease in structuralstrength as lattice defects increase. On the otherhand, the hardness of steel and various alloys canarise from the presence of appropriate amountsof "impurity" elements (e.g., carbon in steel).These impurities alter the properties of the metal.One way that this may be accomplished (and onethat is fairly easy to demonstrate visually withthe models previously used) is the presence of anatom of a different size at a point in the lattice.Imagine this in terms of the figures on page 34and the resulting difficulty of gliding in the topfigure if a large atom "blocked" the glide. Therate of a chemical reaction may depend upon crys-tal defects (they provide a "point of attack").The etching of metal with acids may occur at thedefect site.

The presence of a few atoms of arsenic in theborderline metal germanium increases its con-ductivity (by providing more current-carryingelectrons); crystals such as this are called semi-conductors and are important in solid-state elec-tronics equipment (e.g., transistors).

Some students might enjoy trying to showcrystal defects with the crystal models used insection 1-14.

Note: The remarkable photographs taken byProfessor E. W. Mueller of Pennsylvania StateUniversity (student module, pages 25 and 33)show the actual location of atoms in the crystals.Your students may ask why some of the atomsseem to be arranged in ways familiar to them butthen seem to change to other ways. The answeris that the photograph represents the point of apin, and we are seeing sections of several differentlayers, since the tip was shaped to a point.

MINIEXPERIMENT1-16 GROWTH IS THE NAME OF THE GAME

The purpose of this miniexperiment is to give the stu-dent firsthand experience in "growing" ionic crystals.

33

Concepts

Ionic crystals exhibit regular lattices.Ionic crystals can be very soluble in water.Formation of a crystal from a saturated solution canbe aided by the presence of solid particles (im-purities, or "seeds").

Objective

"Grow" ionic crystals.

Estimated Time One period to prepare. Observationof crystals may take place in successive days.

Student Grouping Pairs or groups of four

Materials

200-300 cm3 saturated copper sulfate200-300 cm3 saturated potassium aluminum sulfate200-300 cm3 saturated ammonium aluminum sulfate200-300 cm3 saturated potassium permanganate60 petri dishes or petri dish covers15 Bunsen burners15 wire gauze, asbestos centers

Advance Preparation To save time and materialsyou may prepare the saturated solutions ahead of timeand provide them as stock solutions. Make a saturatedsolution by dissolving as much salt (see below) as pos-sible in a clean beaker (500-cm3) about two-thirds fullof distilled water. The solution process will be more rapidif the solution is warmed gently. When no more saltappears to dissolve, add a small excess, stir, and allowto stand overnight. The next day, if the excess salt hasdissolved, saturation was not reached; add more saltand repeat.

The solubilities of these salts (in grams per 100 cm3 coldwater) are as follows:

copper sulfate (CuSO4 5H20) 31.6potassium aluminum sulfate KAI(SO4)2 12H201 11.4ammonium aluminum sulfate [NH4 Al(SO4)2 12H20] 1 15.0potassium permanganate (KMnO4) 2.8

You can also make seed crystals by following the abovesteps. To get a larger selection of crystals, allow thesolution to evaporate until nearly dry (several days).Pick out a nicely formed seed crystal.

Laboratory Tips The purpose of bringing the solutionto a boil is to evaporate a portion of the water and thus

34

make the solution supersaturated when it cools. If thestudent heats the solution too briskly, the burner mayhave to be cut off before all of the solution has beenthoroughly heated, or, the solution may boil over witha gush, making a mess. If you are careful, you canhave students return their excess solution decantedfrom crystals and thus save on materials.

Miniexperiment If you would like to use another labactivity earlier in this module to break up some of thestretches of discussion and nonlab experiments, youcan try to grow large crystals, either individually or asa class project.

In order to grow large, regular crystals, three things areimportant: (1) The growing solution must be saturated;(2) a good seed crystal must be used; (3) dust anddirt must be kept out, since they provide nucleating sitesfor little crystals to start. In addition, if the temperaturein the laboratory fluctuates too greatly, uniform growthwill not result. You can stabilize the effect of fluctuatingtemperatures by using a large water bath (a bucket ofwater will do) as a temperature buffer.

Potassium aluminum sulfate [KAI(SO4)2 12H20], or"alum," and potassium chromium sulfate [KCr(SO4)212 H20], or "chrome alum," are very easy to grow. Alumforms clear octahedra, and chrome alum yields purpleoctahedra. Mixed crystals of the above two salts canbe grown in any proportion, since the two compoundsare isomorphous. This results in pink, lavender, or lightpurple crystals. In addition, a perfectly clear and color-less layer of alum can be grown over a purple crystalof chrome alum by changing the solution surroundingthe crystal.

There are several other materials that form interestingcrystals, such as "Rochelle Salt," or potassium sodiumtartrate; nickel sulfate (NiSO4. 6H20 and NiSO4.7H20); copper sulfate (CuSO4 5H20). All of these re-quire somewhat more skill, patience, and careful proce-dure. We recommend Crystals and Crystal Growing,by Alan Holden and Phylis Singer (New York: Doubleday,

1960) for excellent directions on growing crystals. If youreally want to get into growing crystals in a big way,you may be interested in "The Poor Chemist's RotaryCrystallizer," by L. Kershnar and M. P. Goodstein, whichappeared in Chemistry (March 1977), p. 25.

Students enjoy observing microscopic crystal growth.Ask the biology teacher to lend you a few microscopes(you might wipe each objective lens with a damp tissue

42

before returning them), spread a small fraction of a dropof NaCI solution on a microscope slide. Using 100Xmagnification, focus in on the edge of the solution andwatch for crystal growth. Do not concentrate too longon crystals already formed, but watch the region wherecrystals are growing. Growth rate may be acceleratedby warming the slide. Adjust the mirror or light sourceto get either a "dark field" or a "light field" for someinteresting observations. NaCI cubes are unmistakable;however, remind the students that the crystals arethree-dimensional and they must use the microscopeto focus through them. Other solutions that may betried are: lead acetate, copper sulfate, potassium sul-fate, potassium dichromate, potassium chloride, am-monium chloride, sodium bromide, and sodium iodide.

1-17 GETTING A CHARGE

Even though the study of ionic crystal latticesmakes sections 1-17 through 1-20 similar to theprevious ones, it must be pointed out to the stu-dent that the situation here is quite different be-cause we are now dealing with charged particles.Not only does the size of the particles affect thecoordination numbers (as in the metals), but sodo the electrostatic attractions and repulsions.This is brought out in the following miniex-periment.

MINIEXPERIMENT1-18 ATTRACTING OPPOSITES

The purpose of this miniexperiment is to show thestudents an adequate model for the electrostatic at-tractions and repulsions involved in ionic packing.

Concepts

Particles of like charge repel each other, and particlesof unlike charge attract each other.Any physical structure involving charged particleswill be influenced by the interaction of attractive andrepulsive forces.

Objective

Build models of ionic packing systems, using discmagnets to represent the ionic species.

Estimated Time 10 to 15 minutes

43

Student Grouping Pairs or groups of four (depend-ing on the number of disc magnets available).

Materials

100 disc magnets30 plates of glass or clear plastic, 8 x 8 cm (optional)1 overhead projector and screen (optional)10 ring magnets (optional)

Advance Preparations Paint the magnets red andblue, or black and white, or "+" and "" to label theirpolarity. To insure correct coloring of the same polarity,you will find it helpful to stack up the disc magnets. Theythen will be lined up according to polarity, and all youhave to do is successively paint the one on top.

Laboratory Tips Although it looks easy to arrangesix "negative" magnets around a "positive" one asshown in the illustration in the student module (FigureA, page 36), it is impossible. The repulsion from thetwo magnets of similar "charge" on each side of thesixth magnet repels it more strongly than the centralmagnet attracts it. This is not immediately apparent tothe student, however, since the magnets tend to "hopup" on one another, creating the impression that, if youcould just keep them all lying flat, the arrangementwould work. You can show dramatically that it will notwork by fixing one magnet between two parallel platesof glass or clear plastic with shims to allow just a littlespace for movement. (To force the magnets to remainplanari.e., not to "hop up"keep the shims as thin aspossible, consistent with elimination of binding by theplates.)

This arrangement holds the magnets coplanar, and, uponpushing the sixth magnet in, one of the other five isforcibly ejected. If you use an overhead projector, stu-dents will get a kick out of watching attempts to squeezein the sixth magnet.

After students are convinced that a coordination numberof six in a single plane won't work, they can start ex-perimenting, trying to build a stable lattice with theirmagnets. Many will come up with a simple square lattice,and this leads directly into the next experiment. Youcan show this on an overhead projector, too, if you getsome ring magnets with holes in the middle. These canbe marked by pasting strips of paper across the holeso that +'s and 's are formed.

35

It is a good idea to paint the magnets for your ownreference, so that you don't turn one upside down andchange its polarity!

Post lab Discussiondents that the packingstrongly influenced byrepulsion.

It should be clear to your stu-of ions (charged particles) isthe forces of attraction and

EXPERIMENT1-19 PACKING IONS

The purpose of this experiment is to build a model forthe packing structures of sodium chloride (NaCI).

Concept

The structures of ionic crystals are determined bythe attractive and repulsive forces of ions.

Objectives

Construct three-dimensional models of ionic lattices,using plastic balls and boxes.Determine the coordination number of ionic struc-tures.

Calculate the efficiency of packing of ionic structures.



Materials

15 plastic boxes (see 1-14)15 sets of 150 to 200 polystyrene balls, 1" (25 mm)

diameter (Paint half the balls a different color.)

Advance Preparation The format of this experimentis very similar to that of experiment 1-14, and all the gen-eral instructions found there are applicable here. In otherwords, for the experiment to be successful, it will helpa great deal if the teacher has all the transparenciesprepared ahead of time and conducts a running discus-sion as the exercise progresses.

36

Pre lab Discussion The postlab discussion of 1-18can serve as prelab for 1-19.

Post lab Discussion The simple cubic lattice (a goodmodel for the NaCI structure) has a coordination num-ber of 6 (six anions about each cation, and six cationsabout each anion) and a 52.4 percent packing efficiency.The coordination number of the BCC lattice (the modelfor CsCI) is 8 (eight anions about each cation, and eightcations about each anion), and its efficiency is 67.8percent.

Note that although the CsCI lattice (Figure 10, studentmodule page 38) is geometrically related to the BCClattice (Figure 8, page 32), CsCI does not have a body-centered lattice. This is a common error.

Differences in ionic radii and their effects on the latticeadopted by an ionic compound have not been dis-cussed in the student module because the topic is

probably somewhat too involved for the general high-school course. Further, it is difficult or impossible to con-duct packing experiments of the sort done here by usingdifferent-sized ions.

For more advanced classes, this topic can be exploredsomewhat at this time. Models of CsCI and NaCI, madefrom Styrofoam balls of two sizes (like Figures 10 and12, student module page 38) and permanently gluedtogether, are useful and easily made (check experiment1-14). The relation between size and coordination num-ber is illustrated on page 27 of the module; you canillustrate it further with a modification of the overheadprojection of ring magnets (though now of differentsizes) described under Laboratory Tips for section 1-18.

For reference, the ionic radii of some common ions (inangstroms) are:

Li+ = 0.60 Be2+ = 0.31 02- = 1.40 F- = 1.36Na+ = 0.95 Mg24- = 0.65 S2- = 1.84 Cl- = 1.81K+ = 1.33 Ca2+ = 0.99 See- = 1.98 Br- = 1.95

= 1.48 Sr2+ = 1.13 Tee- = 2.21 I- = 2.16Cs+ = 1.69

CO+ = 0.62 Mn2+ = 0.82 Fe2+ = 0.78 Fe3+ = 0.65Co2+ = 0.74 Co3+ = 0.53 Ni2+ = 0.70 Cu2+ = 0.73

The chemist uses a quantity called the "radius ratio"to explain and predict the effect of ion size on the stabilityor crystal lattices. See The Nature of the ChemicalBond, by Linus Pau ling (Ithaca, New York: Cornell Uni-versity Press, 1960) or Inorganic Chemistry: Principles

44

of Structure and Reactivity, 2nd ed., by James E.Huheey (New York: Harper & Row, 1978).

MINIEXPERIMENT1-20 THE EFFECTS OF HANGING TOGETHER

The purpose of this experiment is to show to the stu-dent some of the properties of ionic crystals that arecommonly offered as evidence for the existence of ions.

Concept

Ionic compounds, metals, and nonmetals have dif-ferent and distinct properties.

Objectives

Determine the common physical properties of ioniccompounds.Compare physical properties of metals and nonmetalswith those of ionic compounds.

Estimated Time 15 to 20 minutes


Materials The materials needed for this miniexperi-ment will depend on which properties are chosen forobservation.

Laboratory Tips To allow the teacher some choicein determining which properties are to be investigated,the following possibilities are suggested:

1. Appearance. Examine the specimen for color,

appearance, etc. Examples are NaCI, colorless;CuSO4 5H20, blue; Co(NO3)2 6H20, purple;K2Cr207, orange, etc.

2. Brittleness. Ionic crystals many be shattered readilyby pounding or, more quietly, by crushing in a mortar.Large crystals of alum [KAI(SO4)2 12H20) or photo"hypo" (Na2 S203 5H20) are good.

3. Solubility. Ionic crystals often (but not always) dis-solve in water but do not dissolve in organic solventssuch as toluene. You may simply wish to discussthis without the experiment.

4. High melting point. The high melting point of mostionic compounds can be demonstrated relativelyeasily by heating a little of the compound in a testtube with a Bunsen burner. Some compounds willmelt reluctantly and others will not melt at all.

Suggested: NaCI, 800°C; KI, 723°C; or other alkalihalides. Do not use hydrates, since the salt maydissolve in its own water of crystallization, giving afalse impression of its "melting point."

5. Conductivity. Use the conductivity apparatus fromminiexperiment 1-12. The student can show that

a. solid ionic compounds are nonconductors,b. solutions of ionic compounds in water do con-

duct electricity.

Further, the teacher can demonstrate the conductivityof molten salts by melting an ionic compound witha relatively low melting point. Suggested: NaNO3,m.p. = 307°C; KNO3, m.p. = 334°C; Lil, m.p. =446°C; the last has the advantage of being a simpletwo-element compound, though it requires highertemperatures. Caution: Molten nitrates are verypowerful oxidizing agents. Do not allow them to comein contact with any organic matter!

c. Caution: Conduct this experiment as a demon-stration. Soft glass contains enough ions to con-duct current when molten. You can show howheated glass conducts electricity by using soft(lime, flint) glass tubing as a section in a currentcontaining a light bulb (see illustration). The un-heated glass tube breaks the electric circuit, andthe light bulb remains unlit. Heat the glass tubeuntil the glass begins to flow. The light bulb thenwill glow. As temperature increases, conductivityincreases, since the glass becomes mobile, thusallowing ions ease of movement.

GLASS AS A CONDUCTOR

broken circuitglass rod unheated

45

to 120 volt outlet

37

complete circuitglass rod heated

Post lab Discussion In the discussion following theminiexperiment, in which the properties of ionic com-pounds are interpreted in terms of their structures andthe attraction of oppositely charged ions, good use canbe made of magnets on an overhead projector (seeteacher's guide 1-18). The mechanism for the splittingof crystals discussed in 1-18 can be dramatically illus-trated by means of magnets. Glue the magnets togetherin two strips (otherwise they will tend to shift as youmove them).

Displacing the strip relative to the other by the lengthof one magnet will cause the two strips to fly apart. Theuse of disc magnets with center holes and the "charge"marked "+" or "" with paper strips (see teacher'sguide 1-18) is advantageous if done on an overheadprojector.

Inorganic Molecules

The discussion of inorganic molecules shifts thestudy toward the chemical phenomena empha-sized in the remainder of the module. Covalentmolecules of the nonmetals make up a large partof this unit through a discussion of their chemicaland physical properties. These properties are ex-plained in terms of molecular shape and theeffects nonbonding electron pairs may have onmolecular geometry. Ideas about partial electroniccharge and polar molecules lead to the conceptof hydrogen bonding. The use of balloons, mag-nets, and molecular models makes experiment/-23 a concrete learning experience.

Transition elements present in catalysts andenzymes are introduced through the role theyplay in the synthesis of inorganic molecules suchas ammonia. Finally, algae growth and pollutionare related to phosphates in the environment.

38

1-21 THE COVALENT BOND: SHARE OR ELSE!

This section starts with a review of the stableoctet and covalent bonding studied previously inReactions and Reason: An Introductory ChemistryModule. The octet rule does not explain bonding.It must be looked on as a generalization arrivedat by observation of bond formation. Even thehydrogen atom follows the pattern that the octetrule conveys. Two hydrogen atoms are ener-getically more stable when bonded together thanwhen they exist as separated hydrogen atoms.Since the total capacity of a hydrogen atom istwo electrons, it is following the generalizationstated in the octet rule when it forms a singlecovalent bond. This is the typical behavior ofhydrogen found in almost all of its compounds.

The rare atypical behavior of hydrogen is itsformation of an ionic bond with one of the activemetals. In a reaction with lithium, for instance,under the proper conditions hydrogen will accept

46

an electron and become the negatively chargedhydride ion.

1-22 MOLECULAR SHAPE

The following demonstration can be used to em-phasize the need for using three-dimensionalmodels to illustrate molecular geometry. Once thestructure is visualized, other properties start be-coming evident.

Demonstration Zeus: A simple demonstration willhelp you to reinforce your students' understanding ofisomers. The demonstration also emphasizes the im-portance of observation, problem solving, and modelmaking.

Needed for the demonstration is an object we will callZeus (and henceforth you may wish to refer to thisdemonstration as "Zeus"). The object may be constructedof wood, Styrofoam, cork, or any material easily carvedand painted or colored. Select a convenient dimension(3 to 8 cm) that we will call d. The dimension willdepend on the materials you have to work with. Makea cylinder whose diameter and height are both d unitslong. Draw a line across the face on one end of thecylinder, dividing the face into halves. Begin cutting atthe line on an angle so that the cut terminates at theouter margin of the bottom circle. See the figure here:

1. 2.

Paint eyes and mouth on the full circle face and painteach of the beveled sides a different color, so the figurewill appear like these as shown here when viewed fromdifferent angles.

47

two views of circle

bottom view top view

two views of square

side 1 view side 2 view

two views of triangle

front side view back side view

Now make a template from a piece of cardboard ormanila folder by cutting out a circle, a square, and a tri-angle (not equilateral) of the dimensions shown here.

You can now use Zeus and the template in the creationof a three-dimensional model. Show the students thetemplate and challenge them to construct a solid objectthat will pass through each of the three holes, completelyfilling each hole at some point in passing through it. Giveyour students a chance to design their own Zeus. Then,if necessary, show them how Zeus passes through eachhole in the template. In this instance, Zeus serves as amodel that meets desired specifications.

39

The use of models is also sometimes necessary to illus-trate in some concrete way something that is either tooabstract or is of such a nature that it would not be pos-sible to use the real thing. For example, we cannot bringthe solar system into the classroom, so we use a modelinstead. In chemistry, it is important to have models tohelp understand the structure of individual molecules.Some of the most basic concepts in chemistry dependon one's understanding of molecular structure. Moleculesmay be drawn easily on the board, but we can better usemodels to illustrate the complex structures of manycompounds.

If we place our Zeus model on a surface at eye level, andposition four students at compass point directions aroundthe model, so that each is facing the object and sees onlya single surface, we have established in terms of the ob-ject four different points of reference.

One student sees a red square; another sees a whitesquare; a third sees a red-and-white triangle; and afourth, a white-and-red triangle. If we were to place theobject on a clear surface, another student beneath itwould view a single-color circle, while a person viewingthe object from above would see a half-white and half-red circle. Zeus is also helpful in demonstrating another"difficult to see" concept in chemistry, namely that ofisomerism.

During the observations of Zeus by the students, therewere two different kinds of triangles observed. If studentsdo not realize that they saw very different triangles, havethem reexamine the models by looking at the trianglesand the remainder of the model in relation to the triangle.Hint that the two triangles are mirror images of eachother. Provide a hand mirror to prove it.

Now, if the concept has been developed to this point,by inductive reasoning the next step should also followthat the student can now construct molecular modelsof isomeric compounds. Get out the molecular modelsand get started. Keep Zeus handy, though. He will en-joy the show and besides, one should not cast early idolsso easily aside.

EXPERIMENT1-23 STRUCTURES OF MOLECULES

The purpose of this experiment is to investigate the ge-ometry of some common molecules.

4048

Concepts

Molecules have different geometric shapes.The shape of a molecule is determined by the bondingand nonbonding pairs of electrons available.

Objectives

Write dot structures for molecules.Write line formulas for molecules.Predict the shapes of molecules, including those withnonbonding pairs of electrons.Construct ball-and-stick models of molecules.Write correct formulas for some compounds.Use magnets as models to determine moleculargeometry.Use balloons as models to determine moleculargeometry.

Estimated Time One and one-half to two periods

Student Grouping Pairs or groups of four

Materials

100 disc magnets (See 1-18)150 round balloons15 ball-and-stick model kits (or an adequate substitute:toothpicks and gumdrops, marshmallows, or balls of clay)

Advance Preparation If substitutes are used for themodel kits, the teacher must supply additional instruc-tions regarding the bond angles and directions.

You may wish to use specifically prepared inexpensivekits to accommodate Part 2 of this experiment. Lab-AidsInc., 130 Wilbur Place, Bohemia, New York 11716 pro-duces several student kits with enough materials for upto 50 students. The atoms in each kit consist of plasticnuclei with pegs set at correct bonding angles to produceaccurate three-dimensional models. The kitS containseparate procedures, worksheets, and a teacher's guideprepared by the company. Write the company for pricelist and description.

Prelab Discussion The preliminary discussion shouldcall attention to the number and arrangement of elec-trons in the atoms as they are found in the periodictable. In this experiment only those elements called"representative" are investigated. No element beyondthe second period is considered. Later sections of thismodule will speak of properties and behavior of transition

elements. Note that the first element in a period has oneelectron. Each succeeding element has one more elec-tron than its preceding neighbor. All of the moleculesconsidered in the experiment are characterized by co-valent bonds. Emphasize that covalent bonds arise fromelectrons being shared. Stress that pairs of electronswill be found as far from each other as possible, andstable molecules have all electrons paired.

Laboratory Tips Part 1: Graphic Formulas. Start thisdiscussion by showing the class an example of how dotstructures and line structures are drawn. As studentswork their dot structures and line structures, they shouldsee the difficulty in trying to describe three dimensions.As an exercise, ask them to consider any differences be-tween the two line structures:

CI

HCCICI

HCHCI

The fact that the above two structures represent the samemolecule may be used to introduce Part 2 or may be leftfor discussion at the conclusion of the exercise.

Part 2: Molecular Models. If model kits are limited, theclass may be broken into three groups: "carbon group,""nitrogen group," and "oxygen group."

However, pedagogically it may prove more advanta-geous for students to start by constructing H2, CH4, NH3,and H2O, in that order. They will thus see in a more dra-matic way the need to take into consideration the non-bonding pairs of ammonia and water.

Part 3: Using Magnets to Determine Molecular Geom-etry. This part shows graphically the repulsion betweenlike charges. Although magnets must necessarily beused on a two-dimensional plane, students should beable to visualize how the like charges could be even morewidely separated if allowed to spread over three dimen-sions. This idea is reinforced by Part 4.

Part 4: Using Balloons to Determine Molecular Geom-etry. Notice that the balloons fill all space around theinterlocking necks. The inflated balloons (be sure bal-loons are rigidly inflated and equal in size) are to bevisualized as pairs of electrons. The nucleus that theysurround is invisible but is located at the center, wherethe necks of the balloons are joined.

With this aid, students should be able to visualize pairsof electrons in space around an atom; consequently

49

they should "see" how the number of electron pairsaround the atom and the number of bonds that it

forms give it a characteristic geometry. However, theexperiment does not account for differences in bondangles for molecules that have the same number of elec-tron pairs around the central atom (e.g., CH,, = 109.5°,NH3 = 107°, H2O = 104.5 °). Challenge inquiring stu-dents to try to find balloons with different shapes corre-sponding to bonding and nonbonding electron pairs. Thestudent who is successful in this will be able to reproducequalitatively the geometry of H2O, for example.

WATER MOLECULE GEOMETRY

angle opens

>1091/2°

i<1091/2°

angle closes

The following discussion may help illustrate the differ-ences arising from bonding vs. nonbonding electronpairs:*

In a molecule containing four bonding pairs (e.g., CH4)or four nonbonding pairs (the Ne atom), all pairs of elec-trons will be equivalent and occupy the same amount ofspace. The methane molecule is thus perfectly tetra-hedral and the four electron pairs in neon are presumablyalso arranged in a perfect tetrahedral arrangement (thisis not experimentally verifiable). In a molecule such aswater, however, the four pairs are no longer equivalent.Two pairs have protons (hydrogen nuclei) situated insuch a way that they attract electrons towards them.

*For further discussion, see B. E. Douglas and D. H. McDaniel, Conceptsand Models of Inorganic Chemistry (New York: John Wiley & Sons,1965), pp. 61-62, and J. E. Huheey, Inorganic Chemistry: Principlesof Structure and Reactivity 2nd ed., (New York: Harper & Row, Pub-lishers, 1978), pp. 197-210.

41

The electron clouds of these pairs become somewhatelongated and "thinner" than the clouds of the non-bonded pairs that are attracted only by the central (oxy-gen) nucleus. The latter orbitals will tend to "spread out"and occupy more space about the oxygen than the"thinner" bonding pairs.

It should be pointed out that although the balloon experi-ment may seem to be a little elementary, it truthfully re-flects the behavior of electron pairs as discussed above.The valence-shell electron-pair repulsion (VSEPR) the-ory is currently much used in inorganic chemistry. Somestudents might like to read Peter Dahl's article, "Valence-Shell Electron-Pair Repulsion Theory," in Chemistry(March 1973), pages 17-19. You might read R. J. Gil-lespie's articles on the VSEPR theory in Journal of Chem-ical Education (January 1963), page 295; (January1970), pages 18-23; and (June 1974), pages 367-370.

Use the questions asked in Part 4 and the results ob-tained by your class. Ask the students to derive rulesfor predicting structures of molecules. Reference can bemade to drawings of various molecules in the module.Please note that the students may not be familiar withthe convention

F F

F

F F

indicating that the lower left bond is extending towardthe reader and the dashed bond in the upper right is ex-tending away from the reader. Refer the student to thedrawings of space-filling models. It is good at this pointto reinforce the concept introduced in Reactions andReason: An Introductory Chemistry Module that modelsare only convenient representatives of reality. Note, forexample, that although atoms are spherical, the modelsrepresenting fluorine atoms (student module page 42)are not spherical, because they have to fit together toform the fluorine molecule, the model of which, again, isonly approximately representative of the real molecule.This distinction is an important one and easily forgotten.

ANSWERS TO PROBLEMS

(Student Module page 49)

1. Sulfur hexafluoride (SF6)

42

F F

F

F11/ F

2. Phosphorus pentachloride (PCI5)

CI

Cl

3. Hypochlorous acid (HOC1)

H-0

4. Xenon difluoride (XeF2)

Ole

1-24 A MATTER OF LIFE AND BREATH

The geometry of the carbon dioxide molecule islinear, whereas water is bent. This would makelittle difference if electron pairs were sharedequally between bonded atoms. In these twomoleculescarbon dioxide and wateroxygenpulls the shared electron pairs closer to itself andconsequently farther away from the atom to whichit is bonded. This gives oxygen a small negativecharge and leaves the opposite atom with a smallpositive charge. This is called bond polarity. Thepolarity of certain molecules is an observable fact.A dipole moment may result if the molecule isbent or has a nonsymmetrical shape. Then thesmall negative charge on one side of the moleculeand the small positive charge on the other side willcreate a polar molecule.

The polarity can be looked at as the vector sumof the polarities of the bonds in the molecule. Thedipole moment, tk, is used as a measure of thepolarity of the molecule and is measured in De-bye units (D). Following are some examples ofmolecules with polar bonds.

50

Since the chlorine atoms are sym-metrically distributed around thecarbon, the vector sum of bond po-larities is zero. Carbon tetrachlorideis a nonpolar molecule.

The bond polarity between the twoatoms that make up hydrogen fluor-ide serve here as our example of thesimplest of polar molecules.

The water molecule exists in a linearor bent form with a bond angle closeto 105°. The vectors that result fromthe two polar bonds gives an appre-ciable dipole moment to this mole-cule.

The bond angles in an ammoniamolecule are reduced to 107° by thenonbonding pair of electrons. Theresult of the three polar bonds givesthe ammonia molecule an appre-ciable dipole moment.

ClIT

CI

0

= 1.75 D

= 1.84.D

N

HH.

H

= 1.46 D

Further development along these lines may befound in many textbooks.*

ANSWER TO PROBLEM


Ice floats because it has a lower density than liquid water.This may be stated a different way: a given quantity(mass) of water has a greater volume in the form of icethan in the liquid state. Thus, water is one of the fewliquids that expands as it freezes, with possibly disas-trous effects on automobile radiators.

1-25 SOME IMPORTANT MOLECULES

Demonstration A simple demonstration of the actionof a catalyst is as follows. Place a few cm3 of methanol in

*See R. T. Morrison and R. H. Boyd, Organic Chemistry, 3rd ed. (Boston:Allyn & Bacon, 1973), p. 22 ff.

51

an Erlenmeyer flask and swirl the methanol aroundenough to fill the flask with vapor. Heat a platinum wirebriefly in a burner flame and insert it in the flask (but notinto the liquid). The wire will continue to glow from theheat given off by the reaction

2CH3OH + 02 - 20H20 + 21-120 + heat

(This is the same type of reaction that takes place in thesmall flameless pocket heaters.) The wire will continueto glow for a long time if it is allowed to hang in the flask.If the reaction is allowed to proceed for any length oftime, put the flask in a hood, since the formaldehydeformed is irritating. Copper wire can also be used as acatalyst, but it is less effective than platinum.

The subject of nitrogen fixation is one of muchcurrent interest among chemists working in thearea of bioinorganic chemistry. There is the prag-matic aspect: in a world desperately in need ofincreasing food production to match increasingpopulation, nitrogenous fertilizers are greatly indemand. At the more basic scientific level, sci-entists are intrigued by the question of how theenzyme nitrogenase works in living systems. Theillustrations on page 55 of the student module por-tray the nitrogen-fixating structures in legumesat several levels of organization: (1) the entire le-gume, red clover (upper right), and Austrian peas(upper left); (2) the bacteria-containing root-nodules on clover and soybeans (left); and (3) anelectron micrograph of the actual bacteria in thenodule that are responsible for the nitrogen fixa-tion (lower right).

For a discussion of the current state of researchon nitrogen fixation, see "Biological Nitrogen Fix-ation," by W. J. Brill, Scientific American (March1977), pages 68-81, and J. E. Huheey, InorganicChemistry: Principles of Structure and Reactivity,2nd ed., (1978), pages 758-762.

ANSWERS TO PROBLEMS


1. Na and Fe are metals; H, S, 0, N, and CI are non-metals.

2. (a) H2O; (b) NH3; (c) NaCI; (d) H2SO4; (e) HCI3. Na+ Cl- is ionic; lattice is shown in Figure 12, page 38.

The H2O and NH3 molecules are discussed in sec-tion 1-23 Laboratory Tips; H2SO4 consists of tetra-hedral sulfur with two =0 and two OH groups on it.

43

4. Water, ammonia, and sulfuric acid are discussed inthis section. (These are the compounds anticipatedin this question; HCI will be encountered in the nextsection as an acid cleaner; NaCI is present in blood,perspiration, and sea waterit is also important as amelting agent for ice and as a source of Na and CI.)

EVALUATION ITEMS

These are evaluation items that you may wish to use withyour students at various times during the preceding sec-tion. The correct answer to each question is indicatedby shading.

1. As the sizes of the atoms in a metallic lattice in-crease,

A. the coordination number increases.B. the efficiency of packing decreases.C. the density increases.D. none of the above necessarily happens.

2. The coordination number of the hexagonal closest-packed (HCP) structure is:

A. 6 B. 8 C. 10 D. 12

3. The coordination number of the simple cubic struc-ture is:

A. 4 ; B.; 6 C. 8 D. 12

4. A box 12 x 16 x 6 cm is filled with marbles 2 cmin diameter. Using a certain arrangement, 155marbles are packed. The space occupied by themarbles in the box is 12 x 16 x 5 cm. The volumeof the sphere is given by V = 1.33 x 3.14 x r3.The efficiency of this packing is:

A. 52% B. 82% C.' 68% D. 74%

5. Which of the following are the correct coordinationnumber and efficiency of the cubic closest-packed(CCP) structure?

A. 6; 52% B. 8; 68% C. 12; 68% D., 12; 74%

6. Which of the following statements is false?

A. Conductivity is one of the distinctive charac-teristics of metals.

B. The highly ordered structure of a simple cubiclattice is favored by many metals.

C. The malleability of metals is related to the pre-sence of easy gliding planes in the lattice.

D. The cubic closest-packed structure and the face-centered cubic structure are identical.

44

7. The coordination number of the NaCI ionic struc-ture is:

A. 1 B. 4 C.1 6 D. 8

8. Which of the statements below is true?

A. With a few exceptions, most ionic solids are goodelectrical conductors.

B. The highly ordered structure of a simple cubiclattice is favored by many metals.

C. Most ionic solids have high melting points re-sulting from the electrical forces holding themtogether.

D. The hexagonal closest-packed (HCP) structureand the face-centered cubic (FCC) structureare identical.

9. Consider the following compounds:

HCI CaCl2 CH4II III IV

a. Pure covalent bonding is found in:

A. I B. II C. III

b. Polar covalent bonding is found in:

A. II B. III C. V

H2 NiF2

V VI

D. V

D. VI

10. Which of the following molecules has a nonbondingpair of electrons?

A. PCI, B. CH, C. SF6 none of the above

11. The correct line structure for methylamine, CH3NH2is:

H

A. HCNHH

H2O

H

H H. /B. HCN

H H12. Which of the following

structure?

I A. CO2 B. H2O

H H

C. C=NH/ I

H H

H H

/D. HC=N

\H H

molecules has a linear

C. NH3 D. CH,

13. The correct electron-dot structure for NCI3 is:A. :1:11:1 C. CI:N:CI

9 CI

B. D., :1:F1:1:CI

52

Acids and BasesSince many of the inorganic molecules discussedpreviously react with water to produce acids orbases, it is convenient to consider these sub-stances at this time. The initial definitions of acidsand bases presented are those used to explainreactions occurring in aqueous solution. Hence anacid is an H+ donor, a base is an H+ acceptor,and water is the neutralization product. Rele-vancy is introduced through an experiment inwhich acid or basic substances common in thehome are used in titrations. The concluding sec-tion introduces the Lewis acid-base concept. Abase is an electron-pair donor and an acid is anelectron-pair acceptor. Thus, positive metal ions,Lewis acids, offer a convenient way to introducethe next section, Chemistry of the TransitionElements.

Demonstrations may be used to illustrate theacid and base colors of the indicators noted in themodule. Natural dyes may be included. Tryaqueous solutions or the ethanol extracts of redcabbage, the red skins of radishes, or dark berriessuch as blueberries, fresh, frozen, or even injellies and jams.

1-26 GETTING DOWN TO BASICS(AND ACIDICS)

Emphasis is placed on the idea that acids andbases are "opposites" and thus neutralize eachother, regardless of the definition used. Indicatorsused to determine endpoints in neutralizationtitrations are organic compounds that are weakacids or bases. The indicators change color be-cause they represent an equilibrium situation thatis affected by H30+ or OH- concentrations. Adiscussion of pH has been omitted but may beincluded if desired.

The pH scale is a scale that indicates the relativeacidity or basicity of a solution compared withwater. Values usually range from 0-14, with anyvalue less than 7 indicating an acid and any valueabove 7 indicating a base.

EXPERIMENT1-27 HOUSEHOLD ACIDS AND BASES

Concept

Acids and bases neutralize each other quantitatively.

53

Objectives

Perform an acid-base titration to the correct indicatorendpoint.Calculate the percentage of acid or base in householdcleaners.

Estimated Time Two and one-half periods


Materials

30 50-cm3 burets45 250-cm3 Erlenmeyer flasksphenolphthalein indicator, 1 percent3 liters 1 M NaOH3 liters 1 M HCIvinegarhousehold cleaners (liquid Vanish, Lysol, liquid Sani-

flush, solid Saniflush, Drano)15 double buret clamps15 75-mm diameter funnels1 tube stopcock grease (depending on burets used)

Advance Preparation Three liters 1 M NaOH can beprepared by dissolving 120 g NaOH pellets to make 3liters of solution. Three liters 1 M HCI can be preparedby diluting 250 cm3 concentrated HCI to 3 liters ofsolution.

If a more accurate standard is desired, the NaOH canbe titrated against a primary standard such as KHPh(potassium acid phthalate) and then the HCI solutionis titrated versus the newly standardized NaOH. Moreconveniently, 0.1N HCI and 0.1N NaOH can be pur-chased and used as standards.

You may wish to work up sample problem sheets toillustrate the calculations involved in this experiment.

Pre lab Discussion Demonstrate the use of a buret.Emphasize the need for accuracy in recording the exactendpoint and avoiding parallax in making buret readings.Remind students to swirl the titration vessel constantly.If this is the students' first titration, some time and effortshould be spent on practicing techniques.

Discuss the role and use of indicators. Review the con-cept of molarity and relate it to solution concentrations.It is suggested that a sample calculation be performedbefore the experiment.

45

Caution: Point out to the students that the cleanersinvolved in this experiment are strong acids and basesand should be handled accordingly.

Laboratory Tips For the first part of the experiment,everyone titrates vinegar with NaOH. For the secondpart, try to get an even distribution of acidic and basichousehold cleaners.

Titration of Vanish will be difficult, since the color of theindicator tends to fade. The manufacturers of Vanishare currently adding 0.15% potassium monopersulfate,and this oxidizing agent destroys the indicator. It may berestored by adding 1 drop of 0.1 M KMna, solution.

Acidic cleaners that fizz do so because manufacturerssometimes add sodium bicarbonate to make the userthink that something "is happening" when, of course,all that is happening is that some of the acid presentis wasted! These cleaners will give low results. This couldbe used as part of a postlab discussion. For more on this,see R. Breedlove, "The Chemistry of Toilet Bowl Clean-ers," Chemistry (November 1973), p. 31.

Post lab Discussion Compare results with manufac-turers' claims. Here are some reasonable results.

VinegarLysolLiquid VanishLiquid SaniflushSolid SaniflushSolid VanishBowleneCommercial ammoniaDrano

5% CH3COOH8.5% HCI9.25% HCI7% HCI and 2% 1-12C20,81% NaHSO,75% NaHSO,83% NaHSO428% NH,54.2% NaOH

Note that the manufacturers may change their formula-tions, so check the label on the container. If you wishto run this experiment as an "unknown," you can placeopaque tape over the label or transfer the contents to aflask before presenting the cleaner to the students.

ANSWERS TO PROBLEMS


1. 11.7% HCI2. Fe(OH)3 + 3HCI Fe3+ + 3H20 + 3CI-

1-28 ACIDS AND BASES GO TO WORK

You may wish to amplify this discussion by look-ing up representative industrial processes in-volving acids and bases. You can then relate them

46

to everyday chemistry. Note that acids resultingfrom sulfur pollutants in the atmosphere are dis-cussed on page 87 of the student module and inForm and Function: An Organic Chemistry Moduleand in The Delicate Balance: An Energy and theEnvironment Chemistry Module. Sulfuric acid is agood example. Sulfur dioxide, obtained fromroasting copper ores, for many years was allowedto escape into the atmosphere where "sulfuricacid production" took place.

2Cu2S + 302-0 2Cu20 + 2S022Cu20 + Cu2 S 6Cu + SO2

More recently, use of oxygen-enriched air hasresulted in high-grade sulfur dioxide that can beconverted into sulfuric acid (see student modulepage 56):

2S02 + 02 2903

Although sulfur trioxide will combine with water,as shown in the module, the reaction is slow, andnormally sulfuric acid is used to dissolve bothreactants:

SO3 + H2SO4 * 112520, (disulfuric acid, pyrosulfuric acid,or "oleum") H2O + H2S207 2H2SO4

The reaction of sulfur dioxide with oxygen andwater in the atmosphere (together with a similarreaction for nitrogen oxides) seems to be the mainculprit in the phenomenon known as "acid rain"or "acid precipitation." The pH of heavily in-dustrialized areas in North America and Europehas been measured as lower than 5.6 (the ex-pected pH value for pure water in equilibriumwith ambient concentrations of atmospheric car-bon dioxide). For more on this, see G. E. Likens,Chemical and Engineering News (November 22,1976).

About half of the sulfuric acid produced in-dustrially is used to make fertilizers; ammoniumsulfate can be made directly from sulfuric acidand ammonia (see pages 53-57 for the latter):

H2SO4 + 2NH3---- (NH4)2SO4

Insoluble phosphate rock can be solubilized bysulfuric acid:

Ca3 (PO4)2 + 2H2SO4-->Ca(H2PO4)2 + 2 CaSO,

"superphosphate"

These two simple processes provide fertilizerscontaining the important nutrients: nitrogen,potassium, and sulfur.

54

The high boiling point of sulfuric acid makesit a convenient reagent for the preparation ofvolatile acids:

NaCI + H2SO4 . HCI(g) + NaHSO4

Because it is cheap, sulfuric acid is often the acidof choice if one simply needs a source of hydro-gen ions in an industrial process. The iron andsteel industries use sulfuric acid solutions ("pick-ling baths") to remove oxide scale:

Fe203 3H2 304-.4° Fe2 (SO4 )3 + 3H20

Hot concentrated sulfuric acid is a good oxidizingagent, typified by reactions such as:

Cu + 2H2SO4--> CuSO4 + 2H20 + SO2

Large quantities of sulfuric acid are used in thepetroleum and related industries to oxidize tarsand similar impurities so that they may beremoved.

1-29 WHAT'S IN A NAME?

Lewis acid-base definitions are introduced toillustrate additional ways of defining acids andbases. Emphasize that acids and bases are stillopposites in this definition. The octet rule is usedas the basis for Lewis structures.

There is a difference between accepting a pairof electrons from a Lewis base to form a covalentbond and the complete transfer of an electron toform an ionic bond. It is useful to distinguish be-tween them. Only the first type of reaction isincluded in the Lewis concept. If desired, studentsmay practice writing reactions of this type, usingLewis dot structures:

NH, + BCI,--, H3 NBCI3

A PH3 + 8F3-- Fl3PBF3NH3 + H+--, NH4+

CO + BF3 0 OCBF,B Ag+ + 4NH3--, [Ag(NH3)4]+

Cu + + 4NH3;[Cu(NH3)4]2+

Reactions of Type A are very similar to thatshown in the student module and should presentfew problems. Type B reactions are somewhatmore complicated and may require more dis-cussion (CO has two lone pairs; which does ituse?, etc.).

OC:BF3 [Ag(NH3)4 +] tCu(NF13)4 +1

Note: If you are more familiar with Ag(NH,),+you may have wondered about the above; thetetraammine complex forms in excess concen-trated ammonia.

ANSWERS TO PROBLEMS


1. HCI, H2SO4, and BCI, are acids. Both HCI and H2 SO4

are H+-donors; BCI3 is a Lewis acid.NaOH, NH3, and KOH are bases.

2. 2NaOH + H2SO4 0 Na2SO4 + 2H203HCI + Al(OH)3 . AlC13 + 3H20

H3PO4 + 3NH, --o (NH4)3 PO4Or

3NH3 + 3H20 --o 3NH4+ + 30H-and

3NH4+ + 30H- + H3 PO4

3H20 3NH4+ + P043- o (NH4)3PO4

EVALUATION ITEMS

These are evaluation items that you may wish to usewith your students at various times during the precedingsection. The correct answer to each question is in-

dicated by shading.

1. H2O can act as either an acid or a base. The reac-tion that best illustrates the behavior of water as abase is:

HCI + H2O . H30+ + Cl-B. H2O + NH3 --o NH4+ + OH-C. HCI + NaOH o NaCI + H2OD. H2O + NH2- --o NH3 + OH-

2. In a titration of vinegar the following data weregathered:

Mass of empty flask: 32.5 gMass of flask and vinegar: 73.5 gVolume of 1.0 M NaOH used: 33.5 cm3

55

The percentage of acetic acid (molar mass 60) inthis vinegar sample is:

A. 4.5% B. 4.9% C. 5.3% D. 5.7%

47

3. A commercial household cleaner contains KOH(molar mass 56) as its active ingredient. To deter-mine its strength, a titration was run and the followingresults were obtained:

Mass of cleaner:Volume of 1.0 M HCI used:

6.3 g24.8 cm3

The percentage of active KOH in the cleaner is:

A. 18% B. 20% C. 22% D. 24%

4. Two samples of household cleaners were titrated fortheir ammonia content. The results are as follows:

100 cm3 of cleaner A required 75 cm3 of 0.15 M HCIto neutralize.100 cm3 of cleaner B required 50 cm3 of 0.20 M HCIto neutralize.

If both cleaners cost the same amount per pint, whichis the best buy?

A. cleaner BB. cleaner A

C. both are equalD. cannot tell from data provided

5. Which of the following is a Lewis acid?

A. BF3 B. OH- C. CH3CO2- D. NH3

Chemistry of theTransition Elements

Let us consider certain characteristics of the transi-tion elementstheir beauty and color, for in-stance, and oxidation and reduction concepts.Ligands acting as Lewis bases are discussedaccording to their formation of coordination com-pounds. A series of laboratory syntheses of com-plex compounds permits the student to enjoyusing some new skills. Complex compounds,their colors, and their structures are considered,along with applications. Coordination com-pounds are used in experiments in water soft-ening and solvent extraction. We close with anexperiment in which a complexing agent givesa specific test for the presence of lead, which mayor may not be present in samples brought in bythe students.

1-30 YOU CAN'T LOSE FOR WINNING

Redox reactions are introduced, using traditionaldefinitions of oxidation and reduction. The num-ber of electrons lost by transition metals cannotbe predicted accurately. The idea of multiple oxi-dation numbers stresses the wide range of reac-tions possible for transition metals.

Plan to show the CHEM Study film, VanadiumA Transition Element, if it is available.

48

Demonstration An Inorganic Amoeba: On a watchglass, place a small pool of mercury (about the diameterof a dime). Add 6 M H2SO4 to cover the mercury pool.Add about 1 cm3 of 0.1 M K2Cr202. (KMnO, may alsobe usedjust enough to make the solution pink.)

In the presence of electrolytes the surface tension ofmercury decreases and the pool of metal flattens out.Touch it on the outer edge with a piece of iron wire(nail or needle) and it suddenly contracts. Fix the wirein such a way that the contraction breaks the contact.The mercury will flatten again; touch the wire, it will con-tract again; and so on. This rhythmic pulsing of the mer-cury can be shown to the class by using an overheadprojector. Place a few bits of organic shrubbery aboutthe watch glass and chide the students about the lifeof this "inorganic amoeba." Finally, emphasize that thisis a redox reaction by discussing the equations for thereaction, which are approximately as follows.

First, K2Cr20., and KMnO, are strong oxidizing agentsthat is, they contain metals in high oxidation statesthat are seeking electrons. The mercury is able to fur-nish electrons

Hg Hg+ + e-

meanwhile being oxidized itself. You may notice agrayish film, probably mercury(I) sulfate, forming on thesurface of the mercury. The pool of mercury becomesrelatively electron-poor. Touching the mercury pool with

56

the iron wire (an even better reducing agent or sourceof electrons than mercury) reduces the mercury com-pound (the film disappears) and the iron transfers ex-cess electrons to the mercury pool. The iron is, of course,oxidized in the process:

Fe Fe2+ + 2e-

When the iron loses contact with the mercury, theprocess repeats itself. As to the relation between elec-tric charge and surface tension, we suggest you consultyour physics teacher.

The overall reactions are, therefore, reduction ofdichromate or permanganate:

Cr2022- + 14H+ + 6e- 2Cr3+ + 7H20Mn04- + 8H+ + 5e----*Mn2+ + 4H20

and oxidation of the iron wire:

Fe -p Fe2+ + 2e-

Fe2+ can, of course, be oxidized to Fe3+ by either of theseoxidizing agents, but as long as there is metallic ironpresent it will tend to produce only +2 ions becauseof the reaction:

2Fe3+ + 3Fe2+

The mercury cycles back and forth; in a sense it actsas a catalyst promoting the redox reaction. If studentsask why the oxidizing agent doesn't react directly withthe iron wire, you may answer that it probably does,though slowly, and that there is plenty of iron andoxidizing agent to allow them to react with the mercuryas well. If you care to pursue if further, however, youmight explain that chromate (or dichromate) tends to forma protective film on iron. If the radiator protector youadd after a flush is yellowish, chances are it containschromate. You may find that this seemingly simpledemonstration leads to a very involved discussion.Carry it only as far as the interest and ability of yourstudents warrant.

Although this experiment has been conducted manytimes, we are not aware that anyone has ever com-pletely characterized the products. See J. A. Campbell,Journal of Chemical Education 34 (1957), page 362, orTested Demonstrations in Chemistry, 6th ed. (Easton,Penna.: Chemical Education Publishing Company,1965), pages 138 and 143.

1-31 COORDINATION CHEMISTRY! HOLD ON!

The term ligand is new to the student. Point outthat all ligands are not identical, but all act iden-

57

tically; that is, all ligands must be able to donatea pair of electrons. They are all Lewis bases.

The removal and addition of ligands are readilydemonstrated, using copper(II) sulfate. Place afew crystals of CuSO4 5E120 into a test tube.Hold horizontally and heat over a Bunsen burner.

CuSO4 511,0, CuSO4 + 5H20hydrated-blue anhydrous-white

Water will condense on the wall of the test tube,leaving behind the white anhydrous CuSO4.After this is cool the addition of water to theanhydrous CuSO4 will cause heat to be evolved,with a return to the blue color that characterizesthe hydrated form.

H 0

H-0 I/OH H---0 /02-\Cu 2+ :0\ S

H-07 \OH/ +-0/ v0H H

electron pairs are denoted by --

Four water molecules donate electron pairs tothe copper ion. The fifth molecule of water is heldbetween the tetraaquacopper(II) ion and the sul-fate ion by hydrogen bonds and need not be ofmuch concern.

Note: Avoid excessive heating, indicated by adarkening of the copper sulfate sample and anevolution of irritating SO3 fumes.

Cu SO4 Cu() + SO3black white fumes

EXPERIMENT1-32 GET COORDINATED!

The purpose of the experiment is twofold:

1. To acquaint the student with the synthesis of newcompounds, an area where much of the work ofpracticing inorganic chemists is done.

2. To provide the class with a nice variety of coordina-tion compounds from which it may draw some gen-eralizations about this type of compound.

Concepts

Lewis bases may form coordination compounds withmetallic ions.

49

The properties of coordination compounds are de-pendent on the way the metallic ions and the ligandsshare the electrons.

Objective

Synthesize, isolate, and purify coordination com-pounds.

Estimated Time Two to three periods (depending onthe number of syntheses done)


Materials It is not expected that all students will carryout all of the syntheses. One or two for each pair ofstudents should prove adequate. A judicious assignmenton the part of the teacher will insure a good samplingof all the coordination compounds for discussionpurposes.

Refer to Advance Preparation for specific quantities ofchemicals for each compound being synthesized. Referto the student module for specific apparatus require-ments for each synthesis.

50 -cm3 beakers150 -cm3 beakers250 -cm3 beakers600 -cm3 beakers125-cm3 Erlenmeyer flasks250-cm3 Erlenmeyer flasks10 -cm3 graduated cylinders50-cm3 graduated cylindersBuchner funnels and adapters250-cm3 filter flasksrubber tubingfilter paper, medium weightice

Bunsen burnershot plate (optional)aspirators30-cm3 vialsglass tubing, 6-mm diameterdrying oven (optional)watch glassesring standsringsthermometers 10°C to 110°Cwire gauze, asbestos centers

Advance Preparation You will need the followingquantities of chemicals for each pair of students doing

50

a given synthesis. The amount of chemicals and ap-paratus required depends upon the number of studentsdoing a given synthesis.

Part 1: Some Complexes of Copper(II)

A. Tetraamminecopper(II) sulfate:12.5 g CuSO, 5H2030 cm3 conc. NH,30 cm3 ethanol10 cm3 acetone

B. Bis(ethylenediamine)copper(II) sulfate:12.5 g CuSO, 5H2017 cm3 ethylenediamine40 cm3 ethanol10 cm3 acetone

Part 2: Some Complexes of Cobalt(III)

A. Hexaamminecobalt(III) chloride:1 g powdered charcoal

10 g NH,CI15 g CoCI, 6E12030 cm3 conc. NH330 cm3 30% H20225 cm3 conc. HCI25 cm3 ethanol15 cm3 acetone

B. Sodium hexanitrocobaltate(III):30 g NaNO210 g Co(NO3)2. 6H2018 cm3 9 M HC2H30270 cm3 ethanol10 cm3 acetone

Part 3: Some Complexes of the Ligand Acetylacetone

A. Cobalt(III) acetylacetonate:2.5 g CoCO,20 cm3 acetylacetone (2,4-pentanedione)30 cm3 10% H202

B. Chromium(III) acetylacetonate:2.7 g CrCI, 6H2020 g urea6 cm3 acetylacetone (2,4-pentanedione)

C. Aluminum acetylacetonate:6 cm3 acetylacetone (2,4-pentanedione)6 g Al2(SO4), 18H2030 cm3 6 M NH3 solutionlitmus paper, red and blue

58

D. Iron (III) acetylacetonate:3 g FeCI3. 6H206 cm3 acetylacetone (2,4-pentanedione)30 cm3 6 M NH3 solutionlitmus paper, red and blue

Laboratory Tips The procedures in these synthesesare time-consuming. The usual class period makes itnecessary to introduce shortcuts in order for studentsto make their complex compounds in a reasonableamount of time. Heating, cooling, and allowing time forcrystallizing have been reduced. These shortcuts reduceyield and purity of some compounds. The studentsshould be informed that these are shortcuts and notstandard procedures.

In spite of shortcut measures, some of these synthesesrequire more than one lab period. We have tried to makethem fit two successive days.

Part 1: Some Complexes of Copper(II)

A. Tetraamminecopper(II) sulfate:

The standard preparation for this compound sug-gests letting the solution stand for an hour beforechilling. This would improve crystal size and totalyield, but we feel a 15-minute wait is adequate.Tetraamminecopper(II) sulfate is deep blue. Long,needlelike crystals of this compound can be formedby adding the ethyl alcohol to the blue solution care-fully so that it floats on top. Stopper and set theflask aside, without mixing, for about a week. Thealcohol slowly diffuses into the solution and reducesthe solubility of the solute. The slow growth tendsto produce larger crystals.

B. Bis(ethylenediamine)copper(II) sulfate:

Bis(ethylenediamine)copper(II) sulfate is deep blue.

Part 2: Some Complexes of Cobalt(III)

A. Hexaamminecobalt(III) chloride:

The standard preparation calls for two hours inthe water bath. We have obtained good results withthe present procedure. By the time the experimentis resumed the next day, it will be at room tempera-ture, allowing the student to filter immediately.Hexaamminecobalt(III) chloride is orange-yellow.

B. Sodium hexanitrocobaltate(III):

oxidation and an hour for crystallization. Sodiumhexanitrocobaltate(III) is brown-orange.

The directions for the synthesis of sodium hexanitro-cobaltate(III) call for an air current to be bubbledthrough the reaction flask. Since most laboratoriesdo not have an air source available, a suitable onecan be rigged up using a two-hole stopper and bentglass tubing connected to an aspirator. The suctioncreated will draw air bubbles through the solution,thus enabling the NO produced to escape.

Part 3: Some Complexes of the ligand acetylacetone

A. Cobalt(III) acetylacetonate:

If no oven is available, the crystals may be air-driedovernight. The crystals may be recrystallized, if de-sired, from 50 cm3 of hot toluene to which is added300 cm3 of heptane or petroleum ether. The mixtureis then cooled and filtered. Caution: These solventsare flammable! Cobalt(III) acetylacetonate is darkgreen.

B. Chromium(III) acetylacetonate:

If a steam bath is not available, the beaker may beset in a hot water bath on a hot plate overnight, butbe sure the temperature control is set low enough sothat the solution does not evaporate. Chromium(III)acetylacetonate is purple.

C. Aluminum acetylacetonate:

If desired, the product may be recrystallized by dis-solving in the least possible quantity of toluene andreprecipitating it by the addition of petroleum ether.Caution: These solvents are flammable! Separateon a Buchner funnel and wash once with petroleumether. Dry in air. Aluminum acetylacetonate is white.

D. Iron(III) acetylacetonate:

Iron (III) acetylacetonate is red-brown. The last threesyntheses are very simplemerely mix each oneand filter offalthough the chromium compound re-quires an overnight reaction. All three can be doneby one person without difficulty in two periods.

Post lab Discussion You may wish to collect thesamples in labeled vials prepared by the students andorganize these for use with section 1-33, which servesas the ongoing postlab for this experiment.

1-33 LOOK TO THE RAINBOW

This experiment has been shortened to save time. Common properties of coordination compoundsThe standard preparation involves a 30-minute are discussed with little recourse to experiment

5J 51

because no experimental proof is possible at thislevel. One property that can be gone into insome detail is the color of the complexes, oneof their most striking features. In order to let thestudents come to their own conclusions, we havekept the conclusions in the module to a minimum.This means that in order for this to be effective,you must lead a vigorous discussion, elucidatingand challenging suggestions and ideas from stu-dents. Discussing Answers to Problems is an excel-lent place to start.

ANSWERS TO PROBLEMS

(Student module pages 77-78)

1. The ligand alone does not determine the color:

a. Cu(NH3),,S0, = blueCo(NH3)6CI3 = yellow

b. Cu(en)2S0, = blueCo(en)3CI3 = yellow

c. Co(acac)3 = greenCr(acac)3:= purpleAl(acac)3 = whiteFe(acac)3 = red-brown

No.

2. Although there is some relation between the metalion and the color of a complex, the colors can vary:

a. Cu(NH3),S0, = blueCu(en)2SO4 = blue

b. Co(NH3)6CI3 = orange-yellowNa3Co(NO2)6 = brown-orangeCo(en)3CI3 = yellowCo(acac)3 = green

No.

The following is a short outline of suggestionsfor a lively review and discussion. Note: The firsttwo questions involve further .discussion of twoof the problems on pages 77-78 of the studentmodule.

1. Does the ligand determine the color? The twoammonia complexes are different colors: blue andyellow. There are two* ethylenediamine com-

"In the first edition, we included the preparation of [Co(en)3], butthe simplified procedure that was given for student use was notreliableresults were erratic. (The correct preparation is not difficult,

52

plexes, which are also different: blue and yellow.All four acetylacetonate complexes are differentcolors: green, white, purple, red-brown. Theligand alone does not determine the color.

2. Does the metal ion determine the color? The twoCu2+ complexes are deep blue; three of the fourCo3+ complexes are some shade of orange.Clearly, there does seem to be some relationbetween the color of a complex and the metalion present but, as shown by Co(acac)3, the colorscan vary.

3. What are some further factors? From here on,the discussion can turn any one of several waysand so no attempt has been made to outline it inthe module. In the discussion, students may comeup with some of the following observations:

The original copper sulfate solution was blue,though not so intense as the two complexesformed. Point out that this is a result of a com-plex formed with water molecules: Cu (H2 0) 42+

Ask about the colors formed when Cl- (fromNH, C1 or HC1) was added in Part 2A. The deepblue color is from the CoC142- complex. Askwhy that complex is blue but three other cobaltcomplexes were orange. Try to get someoneto suggest (a) the oxidation state is different,Cott vs. Co3+; (b) there are four ligands insteadof six. (Both answers are correct; both factorsplay an important role in color.) You can con-clude that the metal ion must be in a particularoxidation state [you may wish to providefurther evidence of this in the form of a sampleof copper(I) halide for comparison] and havethe same number of ligands.Pursue the different color of the Co(acac)3 com-plex as compared with the other three. All fourcontain Co3+ and all have a coordination num-ber of 6. The difference is that the orangecomplexes have N-Co bonds. Evidently, thenature of the ligand has some effect.

Pursue the above discussion as long as classinterest and time warrant. You may have studentswho are not willing to drop it at this point and whowill ask why one is yellow and not blue and whynot purple for Al(acac)3, etc. These questions

but it is inappropriate to a short working period. You might con-sider having one student prepare a sample for class discussion. SeeInorganic Synthesis 2:221; 9:162.)

60

are difficult to answer with satisfaction withoutmore theory. If s, p, d, and f electrons have beendiscussed, you can point out that color is as-sociated with metal ions having one or more delectronsthat is, most of the transition metalions. In contrast, Al3+ forms colorless compounds.

Students are often interested in color, and youcan further this interest by discussing the relationbetween the color of a compound and its spec-trum. A compound may be blue because the com-plementary color, red, has been absorbed. Yellowcompounds absorb blue and purple light.

Ask your physics teacher to provide you with asuitable prism and a very bright source of light(such as an arc light). With this equipment you canshow quite nicely how transition metal com-pounds absorb colors. Adjust the lamp and prismuntil a complete spectrum (red, orange, yellow,green, blue, violet) is projected onto a screen orwall. Then place flatsided cells* (beakers will notworkthey bend the light rays) containing solu-tions of CuSO4, Co (NO, )2, etc., in the path of thebeam. In the case of the blue Cu(1-120)42+ complex,or the even more intensely colored Cu(NH3)42+complex,** it will be noted that the red end of thespectrum disappears. The solution is blue becauseit absorbs the reds and oranges, etc.; white lightminus red light equals blue light. This is not somuch chemistry as merely the idea of comple-mentary colors, but the students may be inter-ested in actually seeing the spectrum and howthe red light is absorbed by the solution. It isalso possible to buy a kit that allows the samedemonstration to be performed with a 35-mmprojector. Although we have used it with somesuccess, we find the arc lightprism arrangementmore convenient. (For example, how do you ex-plain to your supervisor why there is copper sul-fate dripping out the bottom of the Carouselprojector?!)

1-34 USING COORDINATION COMPOUNDS

Coordination chemistry is so integral a part ofinorganic chemistry that it is almost impossible to

*These are available in some overhead projection kits or you can makesome from Plexiglas in the same way as the boxes in 1-14.

"In aqueous solution both of these complexes probably have twomore molecules of water attached, but there is little point in addingunnecessary diversionary information for the student.

overestimate its value. In the sections that follow,the student is introduced to some aspects of theuses of coordination chemistry. We here presentyou with a few ideas on coordination compoundsthat you may find interesting and useful whendiscussing them.

First, it should be remembered that almost allaqueous chemistry of metal ions involves coor-dination compounds. Chemists Fred Basolo andRalph Pearson pointed out several years ago: "Itis generally agreed that an aqueous ion such asiron (II) is in reality Fe (H20)62+, or somethingsimilar. . . . Thus, it follows that coordinationchemistry includes the greater part of all inor-ganic chemistry. . . . It can also be said that knowl-edge of complex ions is important in many otherareas, for example, biochemistry, analytical chem-istry, catalysis, electrochemistry, mineralogy, andradiochemistry . . ." (see Basolo and Pearson,Mechanisms of Inorganic Reactions, 2nd ed. [NewYork: John Wiley & Sons, 1967]).

One of the most noticeable properties of com-plexes of transition metals is their color. Fromancient times, we have found uses for intenselycolored coordination compounds as pigments.Minerals such as hematite (Fe203, red), orpiment(As2S 3, yellow), malachite (CuCO3 Cu(OH)2,green), and galena (PbS, black) were crushed foruse in paints, among other things. Since they hadno really satisfactory blue pigment, the Egyptiansinvented a process for the manufacture of blueglass from silica, malachite, calcium carbonate,and sodium carbonate. They also manufacturedred lead (P13304) quite early. Later, pigments con-taining cyano complexes of Fe(II) and Fe(III)(Prussian blue and Turnbull's blue) were em-ployed. More recently, organic dyes have re-placed many inorganic pigments, especially indyeing cloth, but even here inorganic complexes(mordants) may still be important.

Coordination compounds of various kinds areemployed as catalysts. Their ability to accept ordonate electrons or to accept or donate ligands al-lows them to catalyze reactions involving electrontransfer or chemical changes of ligands. Biologicalexamples are called enzymes and are discussedlater in this module. It may be noted in passingthat the poisoning of enzymes discussed on pages93-95 of the student module involves specialaffinities of some ligands for certain metals;for example, mercury is strongly bound by

61 Bign COIF AVAIIRABW

53

sulfur-containing ligands, hence when mercurygets into the body it is strongly bound to (andpoisons) sulfur-containing enzymes. The chemistfights back by using complexing compounds con-taining sulfur, such as British Anti- Lewisite (BAL)

CH,CHCH,I I

HO SH SH

which tend to tie up the mercury and reduce itspoisonous capabilities. As a matter of fact, BALwas invented for a similar purpose, to counteractthe poisonous effects of "Lewisite", a gas used inWorld War I. In this compound the poisonouselement is arsenic, which also has an affinity forsulfur. For more on medical uses of chelatingagents, see A. Magliulio, Chemistry (January1974), p. 25; and Chemical and Engineering News(May 2, 1977).

MINIEXPERIMENT1-35 BATHTUB RINGS AND THINGS

This miniexperiment investigates the effect of hard wateron soap. The role that metal ions play in water hardnessis also considered.

Concept

The presence of certain metal ions leads to "low-sudsing" hard water.

Objective

Determine the effect of different metal ions on thesudsing ability of soap solutions.



Materials

100 cm3 0.1 M aluminum nitrate100 cm3 0.1 M calcium nitrate100 cm3 0.1 M cobalt nitrate100 cm3 0.1 M iron(III) nitrate100 cm3 0.1 M magnesium nitrate1000 cm3 soap solution90 18 x 150-mm test tubes

Advance Preparation To prepare the above solu-

3.0 g soap in 1000 cm3 distilled water3.8 g Al(NO3)3 9H20 in 100 cm3 distilled water2.4 g Ca(NO3)2 4H20 in 100 cm3 distilled water2.9 g Co(NO3)2 6 H2O in 100 cm3 distilled water4.0 g Fe(NO3)3 9H20 in 100 cm3 distilled water2.6 g Mg(NO3)2 6H20 in 100 cm3 distilled water

Laboratory Tips It is wise to check the formulas ofsalts used to prepare solutions; the solutions should be0.1 M. If you plan to do miniexperiment 1-36, some ofthese solutions are required. Look ahead and preparea sufficient amount.

Be sure that your soap solution is truly a soap solution(e.g., Ivory Flakes) and not a synthetic detergent. Thelatter is affected by hard water but does not form soapscum. Also, no water softener can be present in theproduct if the experiment is to work properly. The con-centration of the soap solution should be about 3 g per1000 cm3, although it is not critical. This produces asolution that is roughly 0.01 M.

In order to shorten the length of time consumed by thisexperiment, we have employed only those metals thatform precipitates with soap and have used distilled wateras the only control. If you care to expand the miniex-periment and show that some metal ions are harmlesswith respect to water hardness, you can provide the classwith 0.1 M solutions of ammonium nitrate, sodium nitrate,and potassium nitrate. These will not interfere with thesudsing action of the soap solution.

If you live in a part of the country with very hard water,you can use some tap water as one of the samples.Remember that the concentrations used here are moreconcentrated than in natural waters, so less soap will betied up as "scum" with the natural waters.

Be sure your students realize that the six numberedtubes correspond to the six numbered solutions, a dif-ferent solution in each tube.

Pre lab Discussion Review the mechanism of the ac-tion of soap (Form and Function: An Organic ChemistryModule, 0-41 to 0-43, and Communities of Molecules:A Physical Chemistry Module, p. 53). Some metal ionsrender the soap ineffective by tying up the polar endof the soap molecule and causing the soap to precipitate.

2C,,H35CO2-Na+ + Ca2+ (C,7H35CO2)2Ca + 2Na+

sodium stearate calcium stearate

Using the above equation, discuss the insolubility of thetions, dissolve: calcium stearate as forming the soap scum.

54 62

Post lab Discussion In discussing the result of thisexperiment, point out that the hard water used hereis quite a bit more concentrated than you are apt to findin your water system. This makes the precipitates morevisible. If you live in a soft-water area, do not let yourstudents be misled into thinking that natural hard watergives such startling results as their experiment.

MINIEXPERIMENT1-36 WATER SOFTENING

The purpose of this miniexperiment is to observe theaction of water-softening agents upon the ions thatcause water hardness.

Concept

Hard water may be made soft by the removal of metalions by precipitation or through the formation of coor-dination complexes.

Objective

Determine the effectiveness of different chemicals aswater softeners.



Materials

250 cm3 0.1 M250 cm3 0.1 M100 cm3 0.1 M250 cm3 0.1 M250 cm3 0.1 M250 cm3 0.1 M250 cm3 0.1 M

calcium nitratemagnesium nitrateiron(III) nitratesodium triphosphatesodium carbonatesodium tetraborateNTA (nitrilotriacetic acid, sodium salt)

1000 cm3 soap solution150 18 x 150-mm test tubes

Advance Preparation To prepare the above solu-tions, dissolve:

6.0 g Ca(NO3)2. 4H20 in 250 cm3 distilled water6.5 g Mg(NO3)2. 6H20 in 250 cm3 distilled water4.0 g Fe(NO3)3. 9H20 in 100 cm3 distilled water3.0 g soap in 1000 cm3 distilled water

9.2 g Na, P30,0 in 250 cm3 of water*2.7 g Na2CO3 in 250 cm3 of water5.1 g Na2B4O7 in 250 cm3 of water6.4 g N(CH2C00)3HNa2. H2O in 250 cm3 water

Or

6.6 g N(CH2C00)3Na3 H2O in 250 cm3 water

Either of the last two may be used as the "NTA" solu-tion. The sodium salts of nitrilotriacetic acid are usedbecause they are more soluble.

Laboratory Tips Refer to the tips in the previous ex-periment, 1-35.

Prelab Discussion Introduce this experiment as oneapplication of coordination complexes, sections 1-33 and1-34. The metal ion is from the hard water, while thewater softeners furnish the ligands. Also, some softenersact by simple, direct precipitation:

Na2CO3 + Ca2+ CaCO3(s) + 2Na+

Postlab Discussion In the postlab discussion ofwater softeners, you might wish to discuss ion exchangeresins. These are now used to a great extent in labora-tories (the "distilled water" in your lab may be from anion exchanger, for example). The students may befamiliar with them from the small versions available forpreparing water (often erroneously called "water filters")for steam irons. In a simplified view, ion exchange resinsare organic complexers that can tie up both cations andanions and "in exchange" (hence the name) provideH+ (for the cation absorbed) and OH- (for the anionabsorbed), which combine to form water.

1-37 SOLVENT EXTRACTION:CHEMICAL TWEEZERS

This section discusses the importance of beingable to separate one metal ion from another. Theprocedure discussed and demonstrated in mini-experiment 1-38 is that of solvent extraction. Theprocedure capitalizes on the preferential solubilityof a coordination compound into one of two im-miscible layers.

*Formerly Calgon was an appropriate mixture of phosphate water soft-eners and could be used here. After the phosphate scare, Calgonbecame "low phosphate," with 34 percent Na5P30,,, and 66 percentNa2CO3NaHCO3. See J. R. Van Wazer, Phosphorus and Its Com-pounds: Inorganic Chemistry (New York: Interscience, 1958), p. 776.

6355

MINIEXPERIMENT1-38 CATION LIB

The purpose of this miniexperiment is to provide an ex-ample of the solubilities coordination complexes havein two immiscible solvents and to illustrate extractionphenomena.

Concept

Metallic ions can be separated by formation of coor-dination compounds that have different solubilities inpolar and nonpolar solvents.

Objective

Suggest a method of separating a mixture of coor-dination compounds by using the technique of solventextraction.



Materials

50 cm3 0.1 M iron(III) nitrate50 cm3 0.1 M cobalt(II) nitrate100 cm3 hydrochloric acid, conc.100 cm3 hydrobromic acid, conc. (see Advance Prep-

aration)100 cm3 sodium thiocyanate, saturated250 cm3 methyl isobutyl ketone (4- methyl -2- pentanone)

Advance Preparation To prepare the above solu-tions, dissolve:

1.2 g Fe(NO3)3 in 50 cm3 of water1.5 g Co(NO3)2. 6H20 in 50 cm3 of water100 g NaSCN in 100 cm3 of water

A substitute for hydrobromic acid may be used in thisexperiment. Mix 50 cm3 of concentrated HCI with50 cm3 of a saturated solution of KBr or NaBr. Uponmixing, some of the salt will precipitate; decant and usethe clear solution labeled as HBr.

Pre lab Discussion Section 1-37 provides the intro-duction for this miniexperiment.

Laboratory Tips The saturated NaBr or KBr solutionalone will complex Fe3+, but the solution must be stronglyacid if extraction with MIBK is expected to give good

56

results. Many extractions with MIBK may be necessaryfor weak acid solutionsthis fact offers an opportunityto extend this study to include pH as a significant factorin extraction phenomena.

If you choose to use concentrated HBr as such, be sureto check the precautions for handling on the containerlabel, and other reference sources.

Range of Results

Before MIBK(Color afteradding complex-ing agent)

After MIBKColor of MIBKlayerColor of waterlayer

Fe3+

C/- Br-faint yellow-yellow orange

yellow yellow-orange

SCN-intensered

CI-deepblue

CO 2+

Br SCN-blue

intense bluered

deepblue

Postlab Discussion The complex ion (Fear,)- ex-tracts readily into MIBK while (CoBr4)2- remains in theaqueous phase. This difference in solubilities offers ameans of separating these ions. You might like todemonstrate the separation of Fe3+ and CO2+. The ex-traction is most effective if several separatory funnelsare used.

Prepare a solution containing:

40 cm3 1.0 M Co(NO3)220 cm3 0.1 M FeCI360 cm3 HBr, conc. (see Advance Preparation)

The solution contains a 20:1 ratio of Co2+ to Fe3÷ be-cause of the intensity of color of the iron complex.Point out that it is possible to extract a small amountof one species in the presence of a very large amountof another.

Add the above solution to a 250-cm3 separatory funneltogether with 80 cm3 MIBK. Stopper the funnel and shakebriskly. Allow the solvents to separate and then carefullydrain off the bottom, aqueous layer into a second separa-tory funnel. Be careful not to let any of the MIBK layerslip through. Place the first funnel in a rack where theclass can see it. Now add 80 cm3 MIBK to the solutionin the second funnel and repeat the extraction.

The extractions may be continued several more times.The initial color is very dark from the (FeBr4)- ion.After two or three extractions, the pink color of the[Co(H20)6]2+ ion shows clearly in the aqueous layer,

64

but it is still possible to extract more iron from it. Eventhough there is much more CO2+ than Fe3+ in aqueoussolution; the iron is extracted preferentially.

Extraction procedures such as this are often used inanalytical chemistry to separate metal ions before theirindividual analysis. They are also important industriallyin extracting metals from mixtures.

1-39 KNOCK, KNOCK! WHAT'S THERE?

This short section is a "prelab" discussion forminiexperiment 1-40. Use it to get the studentsinterested in the miniexperiment and discuss withthem methods for testing for lead. See the Pre labDiscussion of 1 -40 for further ideas.

MINIEXPERIMENT1-40 GET THE LEAD OUT!

The purpose of this miniexperiment is to illustrate the useof coordination compounds to detect the presence ofspecific metallic ions.

Concept

The distinctive colors of metallic complexes may beused to identify qualitatively the presence of a par-ticular metal.

Objective

Test qualitatively for the presence or absence of leadin a sample.



Materials

100 cm3 0.1 M acetic acid50 cm3 dithizone solution in TTE (Freon 113 or Du Pont

TF Solvent)

Advance Preparation To prepare the 0.1 M aceticacid, dilute 1.14 cm3 concentrated acetic acid to 200 cm3.

Dissolve 2 mg of dithizone in 100 cm3 of TTE (Freon113). Do not prepare more dithizone than you expectto use in a short time; left standing in a glass bottle, itwill extract enough lead from the glass to turn red!

65

Collecting samples: Samples suspected of containinglead (paint chips, metal seals on wine bottles, metal fromtoothpaste tubes, or pieces of solder) may be used inthe procedure described in the student module.

Pre lab Discussion If The Delicate Balance: An En-ergy and the Environment Chemistry Module has notbeen or will not be taught, concentrate on the usefulnessof the test in detecting lead and its importance in theenvironment. If the module has already been taught,you may wish to concentrate the prelab discussion on thecoordination chemistry and solvent extraction involvedhere. Dithizone forms the complex shown below, whichis more soluble in TTE than in water.

C6H5 C6H5I INHN N=N/ i I/ \

S=---C Pb C =S"N =N' \N NH/

C6H5 6H5

Laboratory Tips The procedure given in the studentmodule is modified from Spot Tests, by Fritz Feigl (NewYork: Elsevier, 1954), the classic reference work of itstype. We have used the procedure to detect lead in stocksolutions, paint chips, solder, and auto exhaust. Aceticacid has been used to solubilize insoluble compounds,but the test is more sensitive when performed in neutralsolution. If more sensitive tests are desired, try the fol-lowing spot test.

A drop of the test solution is spotted on to a small pieceof filter paper. A drop of dithizone solution (0.05%) isplaced on the filter paper next to the previous drop, sothat the two will meet. A reddish color indicates thepresence of lead. Placing the sample in a large beakersaturated with NH3 fumes (from a small amount of con-centrated ammonium hydroxide in the bottom) followedby drying in an oven or otherwise makes the test moresensitive. Be sure to run a blank for comparison.

Auto exhaust deposits collected on filter paper from acold tailpipe can be readily spot tested. Add a coupleof drops of glacial acetic acid to the dirtiest smudge ofcarbon and proceed as above. By turning the filter paperover, you can see the colors unclouded by the spot.

This is an extremely sensitive test for lead, and the im-portance of running blanks, knowns, and minimizingcontamination cannot be overemphasized.

57

References: A. E. Sherword, Metallurgia 80 (1969), p.209; and Kodak Publication No. JJ-5, TLC VisualizationReagents and Chromatographic Solvents.

Post lab Discussion The impact of lead in our en-vironment may generate much discussion. Note that leadpoisoning can be extremely serious, especially in chil-dren. Refer your students to the article by Dale Jenkinslisted on page 101 of their module. Do not let emotion-ally charged discussions divert attention from the use-fulness of this miniexperiment. Stress the use of coor-dination compounds for specific tests and the extremesensitivity of these tests. (The dithizone solution in yourbottle may be pinksee Advance Preparation.)

ANSWERS TO PROBLEMS


1. Any of the equations associated with the synthesesin 1-32 or 1-38 is suitable.

2. Examples discussed in this section include watersoftening, chemical solvent extraction, and qualitativetesting.

3. Although ready formation of coordination compoundsand extensive redox behavior (several oxidationstates) are emphasized in this section, the studentmay recall the earlier discussion (1 -7) where it waspointed out that transition metals are usually lessreactive and stronger than representative metals.

EVALUATION ITEMS


1. An oxidation reaction is best represented by:

A. CH,CO2H NaOH CH,Na + H2OB. CO+ + 4NH, Cu (NH3)42+C. Fe Fe2+ + 2e-D. NH, ± H2O NH4+ + OH-

2. Which of the following is a reduction reaction?

A. Fe2+ Fe3+ + e- C. Fe3+ Fe4+B. Fe+ e- Fe3+ D. Fe3+ + e- Fe2+

3. A ligand commonly encountered in coordination com-pounds is:

A. Fe B. CO+ C. NH, D. BF3

4. The coordination complexes of copper(II) compoundsare frequently:

A. orange B. blue C. white D. red

5. While conducting a series of determinations on hardwater, a student ran out of standard soap solution.With no soap available to prepare a new solution,the student substituted a 10 percent detergent solu-tion, made the necessary solution, and continued withthe experimental work. Discuss this procedure and itsresults.

6. A method that could be used to confirm the presenceof lead in a sample of gasoline is:

A. Place 50 cm3 of gasoline in a dish and let it evapo-rate; then scrape the lead residue together for adisplay.

B. Burn 50 cm3 of gasoline in a dish; since the leaddoesn't burn, it will remain in the bottom of thedish for all to see.

C. Both A and B.D. None of the above.

Bioinorganic Chemistry

We now return to the concept of inorganic com-pounds as pollutants, but, as students will see,with further study we can balance this "BadNews" with "Good News" by considering essen-tial elements and trace elements necessary to

58

living systems. Metalloenzymes and a schematicexplanation of their function, as well as the pro-cess of oxygen transport in animals are con-sidered. The concluding section discusses a redoxreaction that includes a compound necessary inproviding energy for living thingsa compoundthat, fittingly, contains iron, a transition element.

66

1-41 BIOINORGANICS: THE "BAD NEWS"

The discussion of inorganic pollutants is intendedto show that the inorganic chemicals themselvesare not harmful, but the way in which they areused can be harmful. Stress the effects of con-centration and reaction rates in a qualitativemanner.

Cursory reading of newspapers and magazineswill turn up a vast supply of articles and refer-ences to everyday problems stemming fromchemicals in our environment. The latest govern-ment decisions concerning the flight of SSTs inthe United States, aerosol cans, etc., can lead toa very lively discussion of the ozone problem.It must be stressed that although the problem isfar from settled, our uncertainty about the dan-gers involved suggests perhaps a conservativeapproach.

The pictures on page 89 of the student moduleshow Lehigh Gap, Pennsylvania, before and afterthe construction of zinc smelters in the area. Thetop photo was taken in the 1880s; the lower one,in the 1930s. The area around the smelters inLehigh Gap is sparsely vegetated or completelybarren over an area of about 4 850 000 m2. Thesurface soil in the area contains up to 8 percentzinc. See M. J. Jordan, Ecology 56 (1975), p. 78.

In The Delicate Balance: An Energy and the En-vironment Module, pollution-related issues and thechemistry involved are discussed in some detail.If your class will not be studying the environmentmodule, or if time allows, you may wish to havethem pursue these investigations;

1. If there is a large smelting or refining plantin your community, you might ask studentsto suggest the kinds of pollutants associatedwith the manufacturing process and disposalof industrial wastes. What are the effects ofthese chemicals on human beings? On plantand animal life? Have local practices changedin the handling of pollutants in recent years?Because of the social and economic as wellas environmental issues involved, studentsshould be encouraged to consider the num-bers of people each plant employs, the mone-tary costs of correcting pollution, and thehealth hazard for the workers and the com-munity.

2. If yours is a farming community, or if thereare farms nearby, ask students to find out whatkinds of insecticides local farmers use, theirchemical compositions, how long they've beenin use, and ways in which they may be moreeffective and more or less harmful to theenvironment than other insecticides.

3. If there are no local examples of possiblesources of pollution, perhaps students couldresearch the before-and-after aspects of a majorcity, such as London or Pittsburgh, which wastransformed by a drastic change in laws regu-lating heating fuels, waste disposal, and otherhousehold and industrial practices.

Lead the discussion into section 1-42 and thebenefical uses of, and reliance upon, trace metalsin life processes.

1-42 BIOINORGANICS: THE "GOOD NEWS"

About 20 elements represent the chemicals es-sential for the life processes. It may be pointedout that two of these elements, hydrogen andoxygen, account for about 89 percent of the atomsin the human body, and carbon and nitrogen forslightly less than 11 percent. This means that therest, less than 1 percent, must be spread outamong the others. They are considered trace ele-ments, since they are needed in very small quan-titiessome of them so small that their discoverytook place only in recent years as more sophis-ticated analytical techniques were developed.Among the less common trace elements we find:cobalt (an integral component of vitamin 13,2);zinc (needed for growth and function of bloodcells, kidneys, liver, and other organs); chromium(needed for insulin activity); and manganese andmolybdenum (required for normal body growthand metabolism).

1-43 ENZYMES: CHEMICAL MEAT CLEAVERS

The remainder of this section can be looked uponas a further example of trace metal activity anda closer look at the mechanism through whichthe metals operate.

The first example is a metalloenzyme calledcarboxypeptidase A. The zinc in this enzyme usesits coordination bonding to grip and hold peptidechains in position so that the enzymes can thenseparate amino acids from the chain.

59

6 7 BEST COIPY

active site

protein portion of enzyme

Enzymes are a very important class of com-pounds and are discussed not only here, but alsoon pages 54-56 of this module and at some lengthin Molecules in Living Systems: A BiochemistryModule. They are useful in portraying variousfeatures of chemistry: catalysis, reaction rates,"poisoning" of both biological and chemicalsystems, and the importance of stereochemistryand molecular shape.

1-44 TAKE A DEEP BREATH!

Without the complexing ability of the iron inhemoglobin and myoglobin, the blood would beunable to carry sufficient oxygen to the cells ofthe body. The mechanism by which this is accom-plished appears, at first sight, to be an exceed-ingly simple one: Hemoglobin picks up oxygenfrom the lungs and transfers it through the blood-stream to myoglobin in the tissues, which holdsit until the cells need it to oxidize food and supplyenergy. The resultant carbon dioxide dissolves inthe blood and is released in the lungs, completingthe cycle. However, on closer inspection, a num-ber of questions arise: Why does hemoglobintransfer the 02 to the myoglobin? This implies thatthe latter has a stronger affinity, but why? Sincetissues have more CO, and a lower pH (remem-ber, carbonic acid is a weak acid) than the lungs,does pH have any effect on hemoglobin? (Theanswer is "yes"; it's called the Bohr effect.)

As one might expect from a molecule of molecu-lar mass of about 64 500, the mechanisms in-volved when oxygen coordinates to hemoglobin

60

are rather complex but finely tuned to the matterof picking up oxygen where it is abundant (lungs)and dispensing it readily where it is scarce (tis-sues). Closely related to these mechanisms arethe reactions that take place when the abnormalhemoglobin, hemoglobin S, is deoxygenated. Theconsequences of the reactions that follow deoxy-genation of hemoglobin S are responsible for theeffects of the physiological traits, sickle-cell traitand sickle-cell anemia, the latter a serious debilita-tor of black Americans. Consult your biologyteacher for ways in which the two of you cancoordinate discussions to present the inorganicchemistry (page 96, student module*); the bio-chemistry (see Molecules in Living Systems: ABiochemistry Module, page 113); and the physiol-ogy, genetics, and evolution of this disease.**

1-45 REDOX ACTION

The conversion of food into energy is often spokenof as a process of burning the food. In a sense,this is an apt comparison. Ordinary burning is arapid oxidation process that produces heat andlight. The oxidation of food in the body alsoproduces energy, but the processes obviouslymust differ considerably. Use of food must takeplace at body temperature and must be controlledto release energy only as the body requires it.The biological catalyst cytochrome c is involvedin this process. Because it can be readily oxidizedand reduced, it transfers electrons and makes theoxidation process possible.

In normal body metabolism, carbohydrates lib-erate energy at the rate of 4 kcal/g; proteins, alsoat 4 kcal/g; and fats, at the rate of 9 kcal/g* (seeMolecules In Living Systems: A Biochemistry Module).

'See also J. E. Huheey, "Precious MetalsLife's Essentials,"REACTS-1973, Proceedings of the Regional Educators Annual ChemistryTeaching Symposium. College Park, Md., Department of Chemistry,University of Maryland, and J. E. Huheey, Inorganic Chemistry: Prin-ciples of Structure and Reactivity, 2nd ed., (New York: Harper & Row,Publishers, 1978).

"See D. L. Martin and J. E. Huheey, Journal of Chemical EducationVol. 49 (1972), p. 177.

tThe kcal, or kilocalorie, of the chemist is equivalent to the Calorieof the nutritionist and the weight-watcher.

68

MECHANISM OF ACTION OF CARBOXYPEPTIDASE A

STEP 1

OH2

0%/CH2

CH, /H / H

-1\1 -0 H

N

\

I

CH2, 1NCC/ N

H II XR

z,_C_N Zn NH01 -';OH N" \o\ /

N. + /N/ \--7 \HH

NH

peptidechain

STEP 2

0

/C\ /CH2

0 -0 CH2

\ ,... R -H " H" U H\ 5:-. l I ,NN

i''''.---CH2 / \O-'C C/\CH H (:),,,

ZnN/..---C\ N/ \

HO1 OH\ /N. + ,.'N/ \C/ \H

NH

STEP 3

peptidechain

/

Y., 6961

ANSWERS TO PROBLEMS


Fehemoglobin, myoglobin, cytochrome c, all used inrespiration.

02used in respiration by all animals.Hgpoisonous element.COcoordinates preferentially to hemoglobin, causing

asphyxia.Znessential element in many enzymes, including

carboxypeptidase A.Pbpoisonous element.NOcatalyzes the decomposition of 03.S02pollutant from roasting or burning high-sulfur coal,

and so forth; turns to sulfuric acid in the atmosphere.

EVALUATION ITEMS


A Summing Up

This summary provides the chance to discuss theintent of this moduleto obtain an idea of whatinorganic chemistry is and what an inorganicchemist does. A brief review of inorganic chem-istry as presented in this module should be bal-anced by discussions in which students attempt topredict the future activities and value of inorganicchemistry.

ANSWERS TO PROBLEMS


1. a. Acids: HCI, H2S0,, HNO,, H3 PO4; bases: NaOH,KOH, NH3, etc.

b. NaCI, CsCI, CuSO4, etc.c. H2, CH,, NH3, etc.d. BF3, H+, AlC13, etc.

62

1. An inorganic air pollutant of much concern is

A. CuS B. SO2 C. CH, D. H2O

2. The number of elements essential to all living systemsis about

A. 11 B. 87 C. 20 D. 42

3. A fertilizer that would be the least likely to includetrace metals would be

A. fish emulsion. C. compost made from seaweed.B. manure. D. ammonium nitrate.

4. A biological catalyst is

A. an enzyme. C. a carbohydrate.B. an amino acid. D. the N2 molecule.

5. The sole function of cytochrome c is

A. to be a chemical meat cleaver.B. to be continuously oxidized and reduced.C. to carry oxygen through the blood.D. to store oxygen for transport.

e.f.

9.h.

2. a.b.c.d.e.

OH-, Cl-, NH,, etc.Cu(NH3)42+, Co(SCN)42-, etc.Fe, Ca, K, etc.Hg, Pb, etc.

H2 SO4 2KOH K2 SO4 + 2H202Na + Cl2 2NaCIHCO3 + OH- C032- + H2OHCO3- + H30+ CO2 + 2H20P4 + 1 OCl2 4PCI5

3. a. Any of the examples discussed in 1 -25 through1-29

b. See section on Bioinorganic Chemistryc. Conduction of heat and electricity, malleability and

ductility, and mechanical strength

4. 107X might be isolated as KX04 (like KMn04). It willbe a metal (fourth-row transition element) and willmost closely resemble rhenium.

70

AppendixSafetySAFETY IN THE LABORATORY

Proper conduct in a chemistry laboratory is really an extensionof safety procedures normally followed each day around yourhome and in the outside world. Exercising care in a laboratorydemands the same caution you apply to driving a car, riding amotorbike or bicycle, or participating in a sport. Athletes con-sider safety measures a part of playing the game. For example,football players willingly spend a great deal of time putting onequipment such as helmets, hip pads, and shoulder pads toprotect themselves from potential injury.

Chemists must also be properly dressed. To protect them-selves in the laboratory, they commonly wear a lab apron or acoat and protective glasses. Throughout this course you willuse similar items. Hopefully their use will become secondnature to you, much as it becomes second nature for a base-ball catcher to put on a chest protector and mask beforestepping behind home plate.

As you read through a written experimental procedure, youwill notice that specific hazards and precautions are called toyour attention. Be prepared to discuss these hazards with yourteacher and with your fellow students. Always read the entireexperimental procedure thoroughly before starting anylaboratory work.

A list of general laboratory safety procedures follows. It isnot intended that you memorize these safety procedures butrather that you use them regularly when performing experi-ments. You may notice that this list is by no means complete.Your teacher may wish to add safety guidelines that arerelevant to your specific classroom situation. It would beimpossible to anticipate every hazardous situation that mightarise in the chemistry laboratory. However, if you are familiarwith these general laboratory safety procedures and if youuse common sense, you will be able to handle potentiallyhazardous situations intelligently and safely. Treat all chem-icals with respect, not fear.

GENERAL SAFETY GUIDELINES

1. Work in the laboratory only when the teacher is present orwhen you have been given permission to do so. In case ofaccident, notify your teacher immediately.

2. Before starting any laboratory exercise, be sure that thelaboratory bench is clean.

3. Put on a laboratory coat or apron and protective glassesor goggles before beginning an experiment.

4. Tie back loose hair to prevent the possibility of its con-tacting any Bunsen burner flames.

5. Open sandals or bare feet are not permitted in the labo-ratory. The dangers of broken glass and corrosive liquidspills are always present in a laboratory.

6. Fire is a special hazard in the laboratory because manychemicals are flammable. Learn how to use the fireblanket, fire extinguisher, and shower (if your laboratoryhas one).

7. For minor skin burns, immediately immerse the burnedarea in cold water for several minutes. Then consult yourteacher for further instructions on possible additionaltreatment.

8. In case of a chemical splash on your skin, immediatelyrinse the area with cold water for at least one minute.Consult your teacher for further action.

9. If any liquid material splashes into your eye, wash theeye immediately with water from an eyewash bottle oreyewash fountain.

10. Never look directly down into a test tubeview the con-tents of the tube from the side. (Why?)

11. Never smell a material by placing your nose directly atthe mouth of the tube or flask. Instead, with your hand,"fan" some of the vapor from the container toward yournose. Inhale cautiously.

12. Never taste any material in the laboratory.

13. Never add water to concentrated acid solutions. The heatgenerated may cause spattering. Instead, as you stir, addthe acid slowly to the water or dilute solution.

14. Read the label on a chemical bottle at least twice beforeremoving a sample. I-1202 is not the same as H20.

15. Follow your teacher's instructions or laboratory proce-dure when disposing of used chemicals.

This symbol represents three of the common hazards in a chemistrylaboratoryflame, fumes, and explosion. It will appear with certainexperiments in this module to alert you to special precautions in addition tothose discussed in this Appendix.

EST COPY AVAILABNA

71 63

Suggested Readings

Note the references to books and articles that arelisted as footnotes and in the text of this teacher'sguide. You may also wish to consult the list ofsuggested readings published in the studentmodule. For further reading into inorganic chem-istry, you can refer to four inorganic textbooksat the college level:

Cotton, F. A., and Wilkinson, G. Advanced Inor-ganic Chemistry, 3rd ed. New York: John Wiley& Sons, 1972.

Demitras, G. C.; Russ, C. R.; Salmon, F.; Weber,J. H.; and Weiss, G. S. Inorganic Chemistry.Englewood Cliffs, N.J.: Prentice-Hall, 1972.

Huheey, J. E. Inorganic Chemistry: Principles ofStructure and Reactivity, 2nd ed. New York:Harper & Row, 1978.

Purcell, K. F., and Kotz, J. C. Inorganic Chemistry.Philadelphia: W.B. Saunders Company 1977.

Two collections of articles from the Journal ofChemical Education are available:

Galloway, 6., ed. Collected Readings in InorganicChemistry. Easton, Pa.: Chemical EducationPublishing Company, 1972.

Watt, G. W., and Kieffer, W. F., eds. CollectedReadings in Inorganic Chemistry. Easton, Pa.:Chemical Education Publishing Company,1962.

In addition, see these articles in the Universityof Maryland REACTS series (Regional EducatorsAnnual Chemistry Teaching Symposium, heldeach January at the University of Maryland, Col-lege Park): "New Compounds and New Ideas"(1970) and "Precious Metals-Life's Essentials"(1973).

Module Tests

Two module tests follow: one to test knowledge-centered objectives and the other to test skill-centeredobjectives. If you choose to use either or both of thesemodule tests as they are presented here, duplicatecopies for your students. Or, you may wish to selectsome of the questions from these tests that you feelapply to your introductory chemistry course and addadditional questions of your own. Either way, makesure that the test you give reflects your emphasis onthe chemistry that you and your students experiencedin this module. The skill-centered tests will require thatyou set up several laboratory stations containing ma-terials for your students to examine or work with. You

64

may wish to add additional test items to round out thetypes of skills you and your students have workedon. (Answers to the test questions in this section areprovided.) If you wish to use a standard-type answersheet for this test, one is provided in the appendix ofthe teacher's guide for Reactions and Reason: An Intro-ductory Chemistry Module.

ANSWERS FOR KNOWLEDGE-CENTEREDMODULE TEST

1. C; 2. A; 3. B; 4. D; 5. D; 6. D; 7. B; 8. A; 9. D; 10. C;11. C; 12. D; 13a. A; 13b. B; 13c. B; 14. A; 15. C; 16. D;17. C; 18. A; 19. D; 20. C; 21a. B; 21b. B; 22. A; 23. B;24. C; 25. A

72

DIVERSITY AND PERIODICITYKnowledge-Centered Module Test

1. A base that is used in household cleaners is:

A. HCI B. NaHSO4 C. NaOH D. Ca(OH)2

2. The HCO3 ion can act either as an acid or a base.The reaction that best illustrates its action as abase is:

A. HCO3 + H2O * H2003 + OH-B. HCO3 + H2O --> C032 + H304C. HCO3 + OH- --* C032 + H2OD. HCO3- + NH3 --* C032- + NH4+

3. The formation of a coordination compound is rep-resented by:

A. Ca2+ + 201- --* CaCl2B. CrCI3 + 6 NH3 > Cr(NH3)6CI3C. Cu2+ + S042 CuSO4

D. 2Na + 012 > 2NaCI

4. A property of metals that is a result of their latticestructure is

A.

B.

C.

D.

their number of valence electrons.their low ionization energies.their ability to dissolve in acids.their malleability.

5. Coordination compounds have uses

A. in qualitative analysis. C. in enzymes.B. as water softeners. D. all of the above

6. A student determined the ionization energies of fourelements. Their ionization energies relative to

hydrogen are as follows:

H H+ + e- I.E. = 1.00A *A+ + e+ I.E. = 1.32B B+ + eC C+ + eD D+ + e

I.E. = 1.62I.E. = 3.00I.E. = 0.32

The element most likely to be a metal is:

A. A B. B C. C

7. An example of a Lewis acid is:

A. H:N:H C.H H

B. :a: D. H:1::61: :*61:.

D. D

8. Reduction is represented by:

A. Mn3+ + e- * Mn2+B. Na > Na+ + e-C. H30+ + OH- * 2 H2OD. K+ + Cl- --* KCI

9. The coordination number of the darkened ion in thefollowing figure is:

A. 1 B. 4C. 5 D. 8

10. The family of elements requiring one electron toachieve a noble gas structure is called the

A. transition metals. C. halogens.B. alkali metals. D. alkaline earth metals.

11. An ionic bond is

A. the unequal sharing of electrons between twoatoms.

B. the equal sharing of electrons between twoatoms.

C. the transfer of electrons from one atom toanother.

D. the bond formed between two nonmetals.

12. If the compound formed between As and F has theformula AsF5, the predicted geometry of the mole-cule is:

A

'As FFFC.

F, F

As

Fl F

B. Fs ,F

,As

FlD. F

F

13. In a titration 365 grams of a household cleaner con-taining hydrochloric acid were neutralized with 100cm3 of a 1.0 M sodium hydroxide solution.

73

a. The balanced equation for this reaction is:

65

A. NaOH + HCI NaCI + H2OB. Na(OH)2 + 2HCI --> NaCl2 + 2H20C. Na2OH + HCI --> Na2CI + H2OD. NaOH + 2HCI --> NaCl2 + H2O

b. The number of moles of NaOH required was:

A. 0.01 B. 0.1 C. 1.0 D. 100

c. The percentage of hydrochloric acid in thecleaner was:

A. 0.1% B. 1% C. 8% D. 10%

14. Co(NH3)63+ is a complex that has a(an)

A. octahedral structure.B. linear structure.C. tetrahedral structure.D. square planar structure.

15. Two properties of an element were found to be itsability to conduct heat well and its ductility. Thiselement is most likely a

A. nonmetal. C. metal.B. metalloid. D. noble gas.

16. Consider the following statements.

(a) Solid ionic compounds conduct electricity well.(b) Solid ionic compounds are nonconductors.(c) Liquid ionic compounds conduct electricity well.(d) Liquid ionic compounds are nonconductors.(e) Solutions of ionic compounds conduct electricity

well.(f) Solutions of ionic compounds are noncon-

ductors.

Which of the above statements are true?

A. (a), (c), and (e) C. (a), (c), and (f)B. (b), (d), and (e) D. (b), (c), and (e)

17. One hundred six elements are currently known. Ifelement 107 is discovered, it will be similar to ele-ment 75. Element 114 will most likely be similar to:

A. At B. Ce

18. The octet rule is used to

C. Pb D. Pt

A. predict a molecule's formula.B. predict a molecule's conductivity.C. estimate an atom's size.D. predict an atom's coordination number.

19. An example of a biological function in which metalcompounds are known to be involved is

66

A. oxygen transport in the blood.B. electron transport reactions.C. oxygen storage in muscles.D. all of these

20. The two major divisions of the periodic table are the

A.

B.

C.

D.

nonmetals and the noble gases.halogens and the nonmetals.metals and the nonmetals.metals and the metalloids.

21. In an experiment similar to the metal packing ex-periment, a student determined that he or she couldstack 144 balls with a radius of 0.50 cm into a rect-angular box 8 x 6 x 3 cm. (Note that the volumeof a sphere is 1.337113.)

a. The volume occupied by the spheres is:

A. 48.1 cm3B. 75.4 cm3

C. 101 cm3D. 144 cm3

b. The calculated packing efficiency is:

A. 33.2% B. 52.3% C. 70.2% D. 100%

22. A physical property that is periodic in its nature is

A.B.

C.

D.

an element's ionization energy.an element's radioactivity.an element's color.all of these

23. The correct electron-dot representation for the com-pound formed between Si and H is:

A. :Si:H C. H:Si:HH

B. H D. H:Si:HH:Si:H

H

24. At room temperature CO2 is a gas and H2O is aliquid. This difference in physical state is a result of

A. the different acidic strengths of these molecules.B. the different molecular sizes of these molecules.C. the different molecular structures of these

molecules.D. the different molecular masses of these com-

pounds.

25. Three drops of phenolphthalein indicator are addedto an unknown solution and the solution turns red.The solution most likely contains:

A. KOH B. KF C. NaCI D. H2SO4

74

Skill-Centered Module Test

Using the skill-centered test items will require certainadvance preparations on your part. The numerals inthe following list indicate the items for which you willhave to prepare special laboratory stations. Be sure totest each of the lab stations before allowing studentsto determine the answers to the skill-centered items.When students are ready to answer these questions,they should go to the numbered station and followthe directions that are given there and in the printedquestion item. When they finish with the materials atthe station, instruct them to leave the materials inproper order for the next student.

2 Provide four samples of metals labeled A, B, C, andD. Be sure they are all of the approximate same sizeand thickness.

A is copper.B is tin.

C is zinc or lead.D is iron or nickel.

3 Using the plastic boxes, construct four packingmodels, making sure that only one is most efficient.

6 Fill a 50-cm3 buret labeled A with 0.2 M HC1. Dilute10 cm3 of concentrated HC1 to a final volume of500 cm3. Using a funnel, place extra solution in astoppered bottle.

Supply a 125- or 250-cm3 Erlenmeyer flask. Supplya dropper bottle of phenolphthalein. Fill buret Bwith 0.1 M NaOH. Dissolve 2 g NaOH in 500 cm3H2O. Place extra in a stoppered bottle marked baseusing a funnel marked for base use only.

Titrate the sample beforehand so you know theamount needed.

7 Provide a solution of 0.1 M NaH2PO4. Place pHpaper of appropriate range at the station with acolor comparison chart. Be sure to measure the pHyourself.

8 Pieces of different metals marked with code lettersor numbers in red crayon make good objects toweigh. Be sure to weigh them yourself.

9 Small rubber stoppers #0, 1, 2 make good objectsfor this determination. Mark them with code lettersor numbers in red crayon. Provide a graduatedcylinder (25- or 50-cm3) and a beaker of water.

10 Provide three large test tubes labeled 1, 2 and 3.Place 15 cm3 of H2O in each. Add two drops of afood color to tube 1, four drops to tube 2, and sixdrops to tube 3.

Provide a large test tube labeled X. Place 15 cm3of H2O in the tube and add five drops of foodcolor to this tube.

12 Provide three test tubes labeled A, B, and C. Markthe 5 cm3 level on each with a ring. Provide corksthat will fit the test tubes. Provide three beakerslabeled A, B, and C, containing the following:

A. 0.1 M NaC1 0.59 g/100 cm3 H2OB. 0.1 M NaBr 1.05 g/100 cm3 H2OC. 0.1 M Nal 1.50 g/100 cm3 H2O

Provide solution X (0.1 M NaI) in a beaker labeled X.

Provide chlorine water in a stoppered flask.

Provide hexane, another nonpolar solvent, in astoppered flask.

Label this flask solvent.

Place a waste disposal jar for use in emptying thetest tubes.

Chlorine water may be made by bubbling CI,through water or by adding a small amount of acid(HC1) to a chlorine bleach (Clorox). Test this ex-periment before using, to be sure the solutionsare of needed concentration.

ANSWERS FOR SKILL-CENTEREDMODULE TEST

1. B; 2. C; 3. *; 4. C; 5. B; 6. *; 7. *; 8. *; 9. *; 10. D;11. C; 12. C

*Evaluate according to teacher standard

'7567

DIVERSITY AND PERIODICITYSkill-Centered Module Test

Several questions in this section require you to makeobservations and perform chemical manipulations. Thestations where you will do these operations will be in-dicated by your teacher. If the station you are goingto is being used, continue with the test and go back later.

1. Consider the data below for eight elements:

Element A B C D E F G H

IonizationPotential 600 650 700 500 550 660 400 450(eV)

BoilingPoint (°C) 1000 750 500 850 600 450 700 450

AtomicRadius 0.80 0.75 0.70 0.70 0.65 0.60 0.60 0.55

(A)

If you want to place these elements into periods,the smallest number of periods (periods should rep-resent cycles of periodic properties) would be:

A. 2 B. 3 C. 4 D. 1

2. Go to station #2 and examine the four samples ofmetals provided. The most malleable (can beshaped most easily) sample is:

A. A B. B C. C D. D

3. Go to station #3 and examine the four crystal pack-ing models provided. The model that represents themost efficient packing system is:

A. A B. B C. C D. D

4. Using the following data, calculate the efficiency ofthe packing system.

Dimensions of cell(I) (w) (h)

= 8 cm x 5 cm x 3 cmDiameter of ball = 1 cmNumber of balls in box= 100

The packing efficiency is:

A. 41.5% B. 92.5% C. 83.0% D. 33.3%

68

5. Examine the picture of a packing system below. Thecoordination number of the (central) colored atom is:

A. 6 B. 8 C. 10 D. 12

6. Go to station #6 and place 25 cm3 of liquid cleanerfrom buret A into the 250-cm3 Erlenmeyer flask.Add about 25 cm3 of water. Add 2 drops of phenol-phthalein indicator. Now titrate the sample with thebase in buret B. Record the volume of base neededto neutralize the liquid cleaner next to #6 at the bot-tom of your answer sheet.

7. Go to station #7 and use the pH paper providedto measure the pH of the solution. Record youranswer next to #7 at the bottom of your answersheet.

8. Go to station #8 and select one of the objects pro-vided and determine its mass. Record its identifica-tion number and its mass next to #8 at the bottomof your answer sheet.

9. Go to station #9 and determine the volume of oneof the objects provided, using the water displace-ment method. Record its identification number andits volume next to #9 at the bottom of your answersheet.

10. Go to station #10 and examine the three test tubeslabeled 1, 2, and 3 in the test-tube rack. Nowexamine the test tube marked X. The color of X incomparison to the other three tubes is best de-scribed as:

A. same as tube #1B. same as tube #2C. between tubes #1 and 2D. between tubes #2 and 3

76

11. A student synthesized several coordination com-pounds and made observations on their colors.These observations are summarized below.

Ligandacetyl-

Metal Ion C/- acetone NH3

CU 2+ blue black blue

Zn" white black white

Co" red black red

Ni" green black green

In order to complete the laboratory report, the stu-dent had to answer the following question. Whatfactor (s) influence the colors of coordination com-pounds? The student should answer:

A. the ligandB. the metal ionC. both the ligand and the metal ionD. neither the ligand nor the metal ion

12. Go to station #12 where you will find three test tubeslabeled A, B, and C in the test-tube rack. The 5-cm3level is indicated by a ring. Fill each test tube withthe liquid of the same letter. Now add about thesame amount (5 cm3) of chlorine water to each tube.Finally, add 2 cm3 of solvent to each test tube andshake gently. Do not put your finger over the top ofthe tube, but use the cork provided. Now place5 cm3 of liquid X in tube X, add 5 cm3 of chlorinewater and 2 cm3 of solvent, and shake gently,using the cork provided.

Solution X reacts like:

A. solution AB. solution B

77

C. solution CD. none of the above

EMPTY ALL TEST TUBES INTO THE WASTEDISPOSAL JAR BEFORE LEAVING.

69

Materials ListQuantities listed are for a class of 30 students working in pairs.

*Optional Items. These items depend on teacher choice. We have listed substitutions in the experiment discussion. Consult thespecific experiment in the teacher's guide to determine use and quantities.

NONEXPENDABLE MATERIALS

Item Experiment AmountAluminum wire 12* 150 cm*Aspirators 32 15Balances, 0.01-g sensitivityBalls, Styrofoam, 25-mm diameter 14, 19 2500-3000Balls, Styrofoam, 50-mm diameter 14*, 19* 84*Beakers, 50 cm3 32 30Beakers, 150 cm3 32 15Beakers, 250 cm3 32 15Beakers, 600 cm3 32 15Boxes, plastic, and false bottoms 14, 19 15Buchner funnels, 91-mm diameter, and adapters 32 15Bunsen burners 16, 20, 25, 32, 40 15Burets, 50 cm3 27 30Buret clamps, double 27 15Clamps, universal 32 15Conductivity apparatus (dry cell, bulb, and leads) 12, 20 15 setsCopper wire 12* 150 cm*Corks, assortment 9, 35 xDropper bottles, 50 cm3 38* 30*Drying oven 32* 1*Erlenmeyer flasks, 125 cm3 32 15Erlenmeyer flasks, 250 cm3 27, 32 45Filter flasks, 250 cm3 32 15Funnels, 75-mm diameter, and supports 27 15Glass squares, 8 x 8 cm, clear (or clear plastic) 18 30Graduated cylinders, 10 cm3 9, 27, 35, 36 15Graduated cylinders, 50 cm3 32 15Graphite 12* 5 g*Hot plate 32* 1-10*Iron wire 12* 150 cm*Lead wire 12* 150 cm*Magnets, disc, 1 cm 18, 23 100Magnets, ring 18 10Medicine droppers 38, 40 30Model kits, molecular 23* 15*Molybdenum wire 12* 150 cm*Mortar and pestle sets 20* 15*Overhead projector and screen 18* 1*Petri dishes, Pyrex 16 30Platinum wire 12* 30 cm*Ring stands and rings 16, 32 15Rubber stoppers, #6, 2-hole, to fit 250-cm3 flasks (regular-size mouth) 32 15

70

78

Item

Rubber stopper assortmentRubber tubing, heavy wall, 9 mm (3/8") I.D. (15 lengths)ScissorsSeparatory funnels, 250 cm3Test tubes, 18 x 150 mmTest-tube clampsTest-tube racksThermometers, 10°C to 110°CTungsten wireVials, 30 cm3Watch glass, 90-mm diameterWire gauze, asbestos centersZinc wire

EXPENDABLE MATERIALS

ItemAcetic acid, glacialAcetoneAcetylacetone, CH3COCH2COCH3 (2,4-pentanedione)Aluminum nitrate, Al(NO3)3. 9H20Aluminum sulfate, Al2(SO4) 18H20Ammonia, conc., NH3 (ammonium hydroxide, conc. NH,OH)Ammonium aluminum sulfate, NH,A1(SO4)2 12H2OAmmonium chloride, NH4CIBalloons, roundBromine waterCalcium nitrate, Ca(NO3)2. 4H20Charcoal, powderedChlorine water (or commercial chlorine bleach)Chromium chloride, hexahydrate, CrC13 6H20Cobalt carbonate, CoCO3Cobalt chloride, hexahydrate, CoC12 6H20Cobalt nitrate, hexahydrate, Co(NO3)2. 6H20Copper(II) sulfate, pentahydrate, CuSO4 5H20Dithizone (di-phenol-thiocarbazone)Drano, Vanish, Saniflush, etc.Ethanol (ethyl alcohol)Ethylenediamine, H2NCH2CH2NH2Filter paper, medium weight, 9-cm diameter (for Buchner funnels)Filter paper, 12.5-cm diameterGlass tubing, 6-mm diameterGraph paper, linearHydrobromic acid, HBr conc.Hydrochloric acid, HCI conc.Hydrogen peroxide, H202, 30 percentIodine, 12

Iodine solution (12 in KI reagent)

Experiment

1

324389, 20, 35, 36, 38,4035, 36, 383212*

323216, 3212*

Experiment32, 403232353232, 4016

3223

935, 3632932323220*, 32, 35, 3816, 20*, 32402732323240324

3827, 32, 38329, 12°9

40

Amount

1

900 cm15

3

24015

15

15

150 cm*15-1203015150 cm*

Amount150 cm3800 cm3600 cm36 g90 g1000 cm360 g150 g15025 cm311 g15 g100 cm345 g45 g500 g170 g600 g0.1 g1 can each2500 cm3300 cm3200 sheets100

5 m30 sheets250 cm3850 cm31000 cm3

5 g50 cm3

79 71

EXPENDABLE MATERIALS (cont'd)

Item Experiment Amount

Iron(111) chloride, hexahydrate, FeCI3. 6H20 32 45 gIron(111) nitrate, Fe(NO3)3 35, 36, 38 10 gLead nitrate 40 5 gLithium, metal 12* 5 g*Litmus, red and blue 32 15 vials eachMagnesium nitrate, dihydrate, Mg(NO3)2. 2H20 35, 36 12 gMethanol (methyl alcohol) 25 10 cm3Methyl isobutyl ketone (4- methyl -2- pentanone or MIBK) 38 250 cm3Methylene chloride 14 250 cm3Nitrilotriacetic acid, sodium salt, N(CH3COONa)3 (NTA) 36 8 gPhenolphthalein, 1 percent 27 10-50 cm3Potassium aluminum sulfate, KAI(SO4)2. 12H20 16, 20* 100 gPotassium bromide, KBr 9, 38 100 gPotassium chloride, KCI 9 1 gPotassium dichromate, K2Cr20, 20* 10 g*Potassium iodide, KI 9, 20* 2 gPotassium nitrate, KNO3 20* 10 g*Potassium permanganate, KMn04 16 15 gSoap (castile) 35, 36 6 gSodium, metal 12* 10 g*Sodium carbonate, Na2CO3 36 3 gSodium chloride 20* 10 g*Sodium hydroxide, NaOH 27 120 gSodium nitrate, NaNO3 20* 10 g*Sodium nitrite, NaNO2 32 450 gSodium tetraborate, Nat B40, 36 6 gSodium thiocyanate, NaSCN 38 100 gSodium triphosphate, Na5P30,0 36 10 gStopcock grease 27 1 tubeSulfur, lump 12* 50 g*Tape, clear (or glue) 4 1 rollToluene 20*, 32* 900 cm3*Trichlorotrifluoroethane (TTE, Freon 113, or Du Pont TF Solvent) 9, 40 300 cm3Urea, H2NCONH2 32 300 gVinegar 27 500 cm3

8 0

72

Index

Acid(s)defined, 45-47Lewis definition of, 47

Alkali metals, 20Alkali(s). See Base(s)Atom(s)

charges on, 35-36, 42-43coordination numbers of, 24-33,

35-36, 53-54lattices of, 23-33

Base(s)defined, 45-47Lewis definition of, 47

Bondingcovalent, 23, 38, 47ionic, 23, 47metallic, 23polar, 42-43

Bioinorganic chemistry, 58-61

Catalysts, 43, 60Chemical cycles, 12, 14Chemical families, 12-14, 15-20Chemistry

bioinorganic, 58-61inorganic, 11

Compoundscomplexes, 51coordination, 49-50, 53, 57covalent, 38-43

Coordination chemistry, 49, 53-54Coordination number, 24-33Crystal(s)

defects, 33growing, 33-35ionic, 33-35, 37lattice, of metals, 33, 35packing, 24-33

Density, 12Dipole moment, 42

Ductility, 12, 23-24

Electrons, 20, 38-39, 47-49Elements

cycles of, 11-12, 14discovery of, 14-18essential, 58-59families and groups of,

12-14, 15-20heavy, 21periodicity of, 12-14, 17-18periodic properties of, 11-12trace, 59transition, 11, 15, 48

Energy, ionization, 12-13Enzymes, 43, 59-60

poisoning of, 53-54Extraction, solvent, 55-57

Families, in periodic table,12-14, 15-20

Fertilizers, 43

Halogens, 18-20Helium, 14Hemoglobin, 60Hydrogen, 14, 38Hydrogen bonds, 42-43

Ionization energy, 12-15Ion packing, 26Iron, 60

Lattice(s), 22-35of metals, 33, 35

Lead, 57Lewis acids and bases, defined,

45-47Ligands, 49, 52

Magnets, 35-36, 41Mendeleev, Dmitri, 11

Metallic properties, 33Metal(s)

bonding of, 23conductivity of, 12and nonmetals, 12properties of, 23-34

Molecular geometry, 39, 41Molecular models, 40-42Molecule(s)

covalent, 38geometry of, 41inorganic, 38structure of, 40-41

Myoglobin, 60

Nitrogen fixation, 43Nonmetals, properties of,

12

Octet rule, 38Oxidation, 48-49

Periodicity, 10-20Periodic properties, 12Periodic table of the

elements, 19pH scale, 45Pollutants, inorganic,

58-59

Reduction, 48-49

Solvent extraction, 55-57

Transition elements, 11, 15chemistry of, 48

Watergeometry of, 42-43hard, 54softening of, 55

131X27 COPY AVARILABLIF,

8173

Table of International Relative Atomic Masses*

Element SymbolAtomicNumber

AtomicMass Element Symbol

AtomicNumber

AtomicMass

Actinium Ac 89 227.0 Mercury Hg 80 200.6

Aluminum Al 13 27.0 Molybdenum Mo 42 95.9Americium Am 95 (243)** Neodymium Nd 60 144.2

Antimony Sb 51 121.8 Neon Ne 10 20.2

Argon Ar 18 39.9 Neptunium Np 93 237.0

Arsenic As 33 74.9 Nickel Ni 28 58.7

Astatine At 85 (210) Niobium Nb 41 92.9Barium Ba 56 137.3 Nitrogen N 7 14.0

Berkelium Bk 97 (247) Nobelium No 102 (259)Beryllium Be 4 9.01 Osmium Os 76 190.2

Bismuth Bi 83 209.0 Oxygen O 8 16.0

Boron B 5 10.8 Palladium Pd 46 106.4

Bromine Br 35 79.9 Phosphorus P 15 31.0

Cadmium Cd 48 112.4 Platinum Pt 78 195.1

Calcium Ca 20 40.1 Plutonium Pu 94 (244)

Californium Cf 98 (251) Polonium Po 84 (209)

Carbon C 6 12.0 Potassium K 19 39.1

Cerium Ce 58 140.1 Praseodymium Pr 59 140.9

Cesium Cs 55 132.9 Promethium Pm 61 (145)

Chlorine CI 17 35.5 Protactinium Pa 91 231.0Chromium Cr 24 52.0 Radium Ra 88 226.0

Cobalt Co 27 58.9 Radon Rn 86 (222)

Copper Cu 29 63.5 Rhenium Re 75 186.2

Curium Cm 96 (247) Rhodium Rh 45 102.9Dysprosium Dy 66 162.5 Rubidium Rb 37 85.5Einsteinium Es 99 (254) Ruthenium Ru 44 101.1

Erbium Er 68 167.3 Samarium Sm 62 150.4

Europium Eu 63 152.0 Scandium Sc 21 45.0Fermium Fm 100 (257) Selenium Se 34 79.0Fluorine F 9 19.0 Silicon Si 14 28.1

Francium Fr 87 (223) Silver Ag 47 107.9

Gadolinium Gd 64 157.3 Sodium Na 11 23.0

Gallium Ga 31 69.7 Strontium Sr 38 87.6

Germanium Ge 32 72.6 Sulfur S 16 32.1

Gold Au 79 197.0 Tantalum Ta 73 180.9

Hafnium Hf 72 178.5 Technetium Tc 43 (97)

Helium He 2 4.00 Tellurium Te 52 127.6

Holmium Ho 67 164.9 Terbium Tb 65 158.9

Hydrogen H 1 1.008 Thallium TI 81 204.4

Indium In 49 114.8 Thorium Th 90 232.0

Iodine 53 126.9 Thulium Tm 69 168.9

Iridium Ir 77 192.2 Tin Sn 50 118.7

Iron Fe 26 55.8 Titanium Ti 22 47.9Krypton Kr 36 83.8 Tungsten W 74 183.8

Lanthanum La 57 138.9 Uranium U 92 238.0Lawrencium Lr 103 (260) Vanadium V 23 50.9Lead Pb 82 207.2 Xenon Xe 54 131.3

Lithium Li 3 6.94 Ytterbium Yb 70 173.0

Lutetium Lu 71 175.0 Yttrium Y 39 88.9

Magnesium Mg 12 24.3 Zinc Zn 30 65.4

Manganese Mn 25.

54.9 Zirconium. Zr 40 91.2

Mendelevium Md 101

*Based on International Union of Pure and Applied Chemistry (IUPAC) values (1975).**Numbers in parentheses give the mass numbers of the most stable isotopes.

74

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I.

U.S. Department of EducationOffice of Educational Research and Improvement (OERI)

National Library of Education (NLE)Educational Resources Information Center (ERIC)

REPRODUCTION RELEASE

DOCUMENT IDENTIFICATION:

(Specific Document)

.s To6 62O

ltrindiszidititifam tf

Title: Teacher's Guide for Diversity and Periodicity: An Inorganic Chemistry Module

Author(s): James Huheey and Amado Sandoval

Corporate Source:

Chemistry Associates of Maryland, Inc.

Publication Date:

1978

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