Ch 2. Elements, Compounds and Chemical Reactions Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 90 91 92 93...

Ch 2. Elements, Compounds and Chemical Reactions

Brady & Senese, 5th

Ed.

Index

2.1. Elements and atoms are described by Dalton’s atomic theory

2.2 Atoms are composed of subatomic particles2.3. The periodic table is used to organize and correlate facts2.4. Elements can be metals, non-metals, or metalloids2.5. Formulas and equations describe substances and their

reactions2.6. Molecular compounds contain neutral particles called

molecules2.7. Ionic compounds are composed of charged particles

called ions2.8. The formulas of many ionic compounds can be predicted2.9. Molecular and ionic compounds are named following a

system

2.1. Elements and atoms are described by Dalton’s atomic theory 3

Chemical Laws

• The law of conservation of mass - in a chemical reaction, the mass of the reactants (starting materials) will equal the mass of resulting products� Implication: reactions involve the re-organization of

materials.

• The law of definite proportions- the ratio of masses of each element is fixed for a given compound� Implication: Each atom has a fixed specific mass, thus

in unique combinations, the mass ratio is specific


Learning Check:

Magnesium burns in oxygen to form magnesium oxide. If 16.88 g of Mg are consumed and 28.00 g of MgO are produced, what mass of oxygen was consumed?

O Massg 11.12

O Mass 16.88)g-(28.00

O Mass 16.88g28.00g

O MassMg MassMgO Mass

==+=

+=


• Matter consists of tiny particles called atoms

• Atoms are indestructible. In chemical reactions, the atoms rearrange but they do not themselves break apart

Dalton’s Atomic Theory

+


Dalton’s Atomic Theory (Cont.):

• In any sample of a pure element, all the atoms are identical in mass and other properties.

• The atoms of different elements differ in mass and other properties.

• In a given compound the constituent atoms are always present in the same fixed numericalratio.

NaCl has a 1:1 atom ratio on the atomic level and larger


Learning Check:

In a sample of MgO, there are 16.89 g Mg and 11.11 g O. What mass of O would there be in a sample that contains 2.00 g of Mg?

O g 1.32

g 2.00g 11.11g 16.89g

O gx

Mgg 2.00

O g 11.11

Mgg 16.89

compounda for ratio fixedO Mass

MgMass

=×=×

=

=

x

x


Your Turn!

In a sample of an unknown compound, the mass ratio of Cl to C is 47.227g Cl to 4.00 g C. In another sample, there are 0.553 g of Cl. What mass of C would be in this sample?

A. 0.1532 g

B. 6.52 g

C. 0.153 g

D. 0.0468 g

E. None of these


The Law Of Multiple Proportions

When two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

• cements the idea that atoms react as complete (whole) particles.

• chemical formulas indicate whole numbers of atoms- not fractions


Using The Law Of Multiple Proportions

sulfur sulfur

dioxide trioxide

Mass S 32.06 g 32.06 g

Mass O 32.00 g 48.00 g

Use these data to prove the law of multiple proportions


Your Turn!

Two substances are formed from A and B. AB and A2B3. If the mass ratio of A/B in AB is 3.49, what is the ratio of A/B in A2B3?

A. 0.431

B. 3.49

C. 0.286

D. 2.33

E. not enough information given


Proof Of Atoms

• Since the early 1980’s, the Scanning Tunneling Microscope (STM) has been used

• A surface can be scanned for topographical information

• The image for all matter shows spherical regions of matter-- atoms

2.2 Atoms are composed of subatomic particles 15

Cathode Ray Tube (CRT)

A gas filled glass tube that has electrical charge applied at both ends.

Such a tube glows with light and is the precursor of the modern-day television screen.


Discovery Of The Electron By JJ Thomson

• In 1897, Thomson placed a magnet near CRT and noted deflection of the beam

• Repeated experiment with an electrical field and noted that the discharge was deflected by an electrical field toward the (+) plate

• Announced discovery of (-) particle, later named “electron”by Stoney


Determining The Charge On An e-: Millikan


Rutherford’s Alpha Scattering Experiment

Most alpha rays passed right through the Au

A few were deflected off at an angle

1 in 8000 bounced back towards the alpha ray source


Rutherford’s Nuclear Model of the Atom

• Since most of the alpha particles were not deflected, most of the atom is empty space.

• Since some of the particles were deflected, they encountered small particles of the same charge.

• Since some particles were reflected, there must be a small dense area.


Discovery Of The Proton

• Discovered in 1918 in Ernest Rutherford’s lab

• Detected using a Mass Spectrometer


Discovery Of The Neutron

• Chadwick determined that the nuclei of light atoms could be caused to disintegrate by being bombarded by alpha particles.

• In collision of alpha particles with Be, a free neutron was created

• the presence of the neutron confirmed in 1932


Subatomic Particles

Particle Symbol Mass (u) Location Charge

electron 5.48579903(10-4) orbital 1-

proton 1.007276470 nucleus 1+

neutron 1.008664904 nucleus 0

-01 eor e−

+Hor 11

11 p

010 nor n


• Dalton’s atomic theory states that atoms of an element have a constant, characteristic atomic massor atomic weight measured inamu (u)

• Atomic masses are based on a standard mass, that of an atom of C

• 1 atom of Carbon-12 = 12 u

• Thus 1 u = 1/12 the mass of a Carbon-12 atom

Atomic Mass


• Most elements in nature are uniform mixtures of two or more kinds of atoms with slightly different masses

• Atoms of the same element with different masses are called isotopes� For example: there are 3 isotopes of hydrogen and 4

isotopes of iron

• Chemically, isotopes have virtually identical properties

Isotopes


Atomic Notation

• An element is a substance whose atoms all contain the identical number of protons, called the atomic number (Z)

• Isotopes are distinguished by mass number (A):� Atomic number, Z = number of protons

� Mass number, A = (number of protons) + (number of neutrons)

� Note that for atoms, A is greater than Z: the symbol is top-heavy

• For charge neutrality, the number of electrons and protons must be equal

SyAZ


This information can be summarized:

� Number of protons = 92 ( = number of electrons)

� Number of neutrons = 143

� Atomic number (Z) = 92

� Mass number (A) = 92 + 143 = 235

� Chemical symbol = U

Mass number, A (protons + neutrons) �Chemical Symbol �

Atomic number, Z (number of protons) �

235U

92

Example: uranium-235


Learning Check:

Fill in the blanks:

symbol neutrons protons electrons60Co

81Br

36 29 29

33 27 2746 35 35

Cu6529


Your Turn!

How many neutrons are there in 52Fe?

A. 52

B. 55

C. 26

D. none of these


Naturally occurring chlorine is a mixture of two isotopes. In every sample of this element, 75.77% of the atoms are chlorine-35 and 24.23% are chlorine-37. The measured mass of chlorine-35 is 34.9689 u and that of chlorine-37 is 36.9659 u. Calculate the average atomic mass of chlorine.

Learning Check: Atomic Mass

100

(75.77×34.9689) + (24.23×36.9659) u

35.45 u


Your Turn

There are 2 isotopes of element Z. The first is 56.5% in abundance and has a mass of 152.3 u. If the atomic mass is 155.5 u, what is the mass of the other isotope?

A. 156 u

B. 44.5 u

C. 157. u

D. not enough information given

E. none of these 153.7 u

2.3. The periodic table is used to organize and correlate facts 31

Periodic Table1A 2A 3A 4A 5A 6A 7A 8A

1 2

H He

3 4 5 6 7 8 9 10

Li Be B C N O F Ne

11 12 13 14 15 16 17 18

Na Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl Ar

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

87 88 89 104 105 106 107 108 109 110 111 112 114

Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Uuu Uub Uuq

58 59 60 61 62 63 64 65 66 67 68 69 70 71

Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

90 91 92 93 94 95 96 97 98 99 100 101 102 103

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

arranged in numbered rows –“periods”columns called “groups” or “families”


• Summarizes chemical and physical properties of the elements

• Mendeleev first arranged atoms by increasing atomic mass. Noted repeating (periodic) properties

• Modern table is arranged by increasing atomic number (Moseley)

Periodic Table


• A groups = representative elements or main group elements

I A = alkali metals II A = alkaline earth metals

VII A = halogens VIII = noble (also inert) gases

• B groups = transition elements

• Inner transition elements = elements 58 – 71 and 90 – 103

58 – 71 = lanthanide elements

90 – 103 = actinide elements

Some Important Classifications:


The modern periodic table

2.4. Elements can be metals, non-metals, or metalloids 35

Metals, Nonmetals, And Metalloids


Your turn!

Which of the following is correct?

A. Cu is a representative transition element

B. Na is an alkaline earth metal

C. Al is a semimetal in group IIIa

D. F is a representative halogen

E. None of these are correct


• reflect light (have metallic luster)

• Can be hammered or rolled into thin sheets (are malleable) and can be drawn into wire (are ductile)

• Are solids at room temperature (except Hg)

• conduct electricity and heat

Properties Of Metals


Nonmetals And Metalloids

• Nonmetals� Lack the properties of metals

� Tend to pulverize when struck with a hammer

� Non-conductors of electricity and heat

� Many are gases, a few solids, and one liquid (Br)

� React with metals to form (ionic) compounds

• Metalloids� Have properties between metals and nonmetals

2.5. Formulas and equations describe substances and their reactions 39

• Are symbols used to describe other elements in a compound

• elements and compounds• Free elements are not combined with another

element in a compound. Examples: Fe (iron), Na (sodium), and K (potassium)� Many non-metals occur in groups of 2 (as diatomic

molecules)- H, O, N, F, Cl, I, Br� Some elements occur as molecules: P4, S, S8, P10, O3 ,

etc…

Chemical Formulas


• Specify the composition of a substance

• Fe2O3 is composed of the elements iron and oxygen in a 2:3 ratio

• CO(NH2)2 expands to CON2H4, but parentheses often group atoms to show the compound’s structure

Chemical Formulas (Cont.)


Hydrates

• Hydrates are crystals that contain water molecules, for example plaster: CaSO4 •2H2O� When all the water is removed (by heating), the solid

that remains is said to be anhydrous (without water)

CuSO4CuSO4 •5H2O

Typical constituents of Portland clinkerCement industry style notation under CCN

2-10%GypsumCaSO4 · 2 H2O

0-18%C4AFTetracalcium aluminoferrite(CaO)4.Al2O3.Fe2O3

0-13%C3ATricalcium aluminate(CaO)3.Al2O3

7-32%C2SDicalcium silicate(CaO)2.SiO2

45-75%C3STricalcium silicate(CaO)3.SiO2

Mass%CCNClinker

Concrete formationCement chemist notation: C3S + H2O → CSH(gel) + CaOHStandard notation: Ca3SiO5 + H2O → (CaO)•(SiO2)•(H2O)(gel) + Ca(OH)2Balanced: 2Ca3SiO5 + 7H2O → 3(CaO)•2(SiO2)•4(H2O)(gel) + 3Ca(OH)2


Learning Check: Count The Atoms In A Chemical Formula

• Na2CO3

• (NH4)2SO4

• Mg3(PO4)2

• CuSO4•5H2O

• ___Na, ___ C, ___ O

• ___N, ___H, ___S, ____O

• ___Mg, ___P, ____O

• ___Cu, ___S, ___O, ___H

32 12 8 1 43 2 81 1 9 10


• 2 HCl(aq) + CaCO3(s) � CaCl2(aq) + H2O(l) +CO2(g)

� HCl and CaCO3are called reactants� CaCl2, H2O,CO2 arecalled the products� Reactants are separated from products with “�”

that means “yields”• States matter: for solids use (s), liquids (l), gases (g),

and for substances dissolved in water (aqueous solutions) use(aq).

• We will learn later that the behavior of the reactants differs based on their states!

Chemical Equations


Balanced Equations

• The number of atoms of each type must remain the same on each side of the arrow

• subscripts must not change-they define the identity of the substances

• Coefficients- numbers in frontof formulas-- indicate the number of molecules of each type

• Balancing achieved by adjusting coefficients 2 H2 + O2 →2 H2O


Balanced EquationsNote that the number of each type of atom balances

and that the coefficient applies to the entire formula

2.6 Molecular compounds contain neutral particles called molecules 47

• Molecules are neutral particles made of 2 or more atoms.

• Many molecular compounds contain hydrogen:

Group NoblePeriod IVA VA VIA VIIA Gas

2 CH4 NH3 H2O HF Ne3 SiH4 PH3 H2S HCl Ar4 GeH4 AsH3 H2Se HBr Kr5 SbH3 H2Te HI Xe

Molecules Form When Nonmetallic Elements Combine


Alkanes

• Alkanes are hydrocarbons (contain only C and H)

• Always have a ratio of atoms CnH2n+2

• Named using a prefix designating the number of C

• All have –ane suffix.

C

1

2

3

4

5

6

7

8

9

10

Prefix

Meth-

Eth-

Prop-

But-

Pent-

Hex-

Hept-

Oct-

Non-

Dec-

Suffix

+ane

Name

Methane

Ethane

Propane


Learning Check: Name that alkane

• ethane

• butane

• octane

Your turn!

Which of the following is heptane?

A. C6H12

B. C7H14

C. C6H14

D. C7H16

Your turn!

Which is the correct name for C4H10?

A. methane

B. ethane

C. propane

D. pentane

E. none of thesebutane


Other Organic Compounds

Alkenes- hydrocarbons with fewer H than the alkanes. CnH2n. Use the same prefixes, but have the suffix -ene. � C2H4 : ___________ � C3H6: _____________propylene

ethylene


Other Organic Compounds (Cont.)

Alcohols- Replace one H in an alkane with an -OH group

• Same prefixes, suffix becomes –anol� CH3OH is ____________� C2H5OH is _______________

methanol

ethanol

Your Turn!

What is the name of CH3CH2CH2CH2OH?

A. butanol

B. propanol

C. pentanol

D. tetranol

E. none of these

Your Turn!

What is a formula for heptene?A. C6 H12

B. C7H14

C. C6H14

D. C7H16

E. none of these

2.7 Ionic compounds are composed of charged particles called ions 56

Ionic Compounds

• Positively charged ions are called cations

• Negatively charged ions are called anions

• subscripts in the formula always specify the smallest whole-number ratio of the ions needed to make a neutral combination (formula unit)

Fe OO2-Fe3+3232


What About Ions?

• Number of p+ = number of e- if neutral

• Number of p+ < number of e- if negative

• Number of p+ > number of e- if positive

• The number of p+ never changes when ions form

How does Ca form Ca2+? Ca loses 2 electrons

How is N3- formed? N gains 3 electrons


Learning Check:

Fill in the blanks:

Symbol neutrons protons electrons60Co3+

81Br-

36 29 27

33 27 24

46 35 36+265

29Cu


The Charges On Many Representative Elements Can Be Predicted

• Noble gases are especially stable • Main group elements will often gain or lose

electrons to have the same number of electrons as the nearest noble gas

• Metals form cations by losing electrons � What is the expected charge on:Ca? Na?

• Nonmetals form anions by gaining electrons� What is the expected charge on:N? O?

2+ +

3- 2-

2.8 The formulas of many ionic compounds can be predicted 60

Rules For Writing Formulas Of Ionic Compounds

• The cation is given first in the formula• The subscripts in the formula must produce an

electrically neutral formula unit• The subscripts should be the set of smallest whole

numbers possible• The charges on the ions are not included in the

finished formula of the substance


Ionic Compounds Are Neutral

• The positive charge must balance the negative charge

• We could use trial and error to find the least common charge

-

+

-

+

-

+


Determining The Formula Of An Ionic Compound

• Practically, we can often accomplish this by making the charge magnitude(not the charge) of one ion into the subscript for the other. (The “Criss-cross” rule)

• If you choose this approach, make sure that the subscripts are reduced to the lowest whole number.

Al3+ O2-

Mg2+ O2-

NH4+ PO4

3- (NH4)+ (PO4)

3- (NH4)3PO4

Mg2+ O2- MgOAl 2O3Al 3+ O2-

Your Turn!

Which of the following is the correct formula for the formula unit composed of potassium and oxygen ions?

A. KO

B. KO2

C. K2O

D. none of these

Your Turn!

Which of the following is the correct formula for the formula unit composed of Fe3+ and sulfide ions?

A. FeS

B. Fe3S2

C. Fe2S3

D. none of these


Transition Metals

Chromium Cr2+, Cr3+ Zinc Zn2+

Manganese Mn2+, Mn3+ Silver Ag+

Iron Fe2+, Fe3+ Cadmium Cd2+

Cobalt Co2+, Co3+ Gold Au+, Au3+

Nickel Ni2+ Mercury Hg22+, Hg2+

Copper Cu+, Cu2+

Post-transition Metals

Tin Sn2+, Sn4+ Lead Pb2+, Pb4+

Bismuth Bi3+

Transition And Post-transition Metals Usually Have Multiple Charges


Some Polyatomic Ions (Ions With Two Or More Atoms):

NH4+ Ammonium ion CO3

2- carbonate ion

OH- hydroxide ion H3O+ hydronium ion

NO2- nitrite ion SO3

2- sulfite ion

NO3- nitrate ion SO4

2- sulfate ion

ClO2- chlorite ion CrO4

2- chromate ion

ClO3- chlorate ion Cr2O7

2- dichromate ion

PO43- phosphate ion

2.9 Molecular and ionic comounds are named following a system 67

• Cations: � If the metal forms only one positive ion, the cation

name is the English name for the metal� If the metal forms more than one positive ion, the

cation name is the English name followed, without a space, by the numerical value of the charge written as a Roman numeral in parentheses

• Anions:� monatomic anions are named by adding the “–ide”

suffix to the stem name for the element� polyatomic ions use the names in Table 2.5

The Stock System Of Naming Ionic Compounds


Chemical Name as Name asSymbol Stem First Element Second Element

O ox- oxygen oxideN nitr- nitrogen nitrideP phosph- phosphorus phosphideCl chlor- chlorine chlorideI iod- iodine iodide

Naming Binary Molecules

The first element in the formula is identified by its English name, the second by appending the suffix –ideto its stem


Naming Binary Covalent Molecules

• Format:number prefix + 1st element name number prefix + stem_ide for 2nd element.

• Greek prefixesmono- = 1 (omitted on 1st atom) hexa- = 6

di- = 2 hepta- = 7

tri- = 3 octa- = 8

tetra- = 4 nona- = 9

penta- = 5 deca- = 10


Learning Check: Name The Following

• PF5 =

• HCl =

• N2O4 =

•phosphorus pentafluoride•hydrogen chloride•dinitrogen tetraoxide

or dinitrogen tetroxide

Your Turn!

Which is the correct formula for nitrogen triiodide?

A. N3I

B. NI3

C. NIO3

D. N(IO3)3

E. none of the above

Your Turn!

Which is the correct name for P4O10?

A. phosphorus decoxide

B. tetraphosphorous decoxide

C. tetraphosphorus decoxide

D. tetraphosphorus oxide

E. none of these


Learning Check: Name The Following

• Na2O

• K2O

• NH4ClO3

• Mg(C2H3O2)2

• Cr2O3

• ZnBr2

•sodium oxide

•potassium oxide

•ammonium chlorate

•magnesium acetate

•chromium(III) oxide

•zinc bromide


Learning Check: Determine The Formula

• calcium hydroxide� Ca(OH)2

• mercury(I) nitride� (Hg2)3N2

• ammonium phosphate� (NH4)3PO4

Your Turn!

Which is the correct name for Cu2S?

A. copper sulfide

B. copper(II) sulfide

C. copper(I) sulfide

D. none of these

Your Turn!

Which is the correct formula for ammonium sulfite?A. NH4SO4

B. (NH4)2S

C. NH4S

D. none of these (NH4)2SO3

78

Overview: Molecules vs. Formula Units

• electrically neutral, discrete particles called molecules

• Neutral groups of charged particles calledformula units

79

Hardness and brittleness� Molecular compounds tend to be soft and easily crushed

because the attractions between molecules are weak and molecules can slide past each other

� Ionic compounds are hard and brittle because of the strong attractions and repulsions between ions

Summary of Properties

80

To melt the a solid, there must be sufficient kinetic energy to overcome the attractions between particles� Molecular compounds have weak attractions between

particles and so tend to have low melting points � Many molecular compounds are gases at room

temperature� Ionic compounds tend to have strong attractions so they

have high melting points � Nearly all ionic compounds are solids at room

temperature

Melting Points

81

• Requires the movement of electrical charge

• Ionic compounds:� Do not conduct electricity in the solid

state

� Do conduct electricity in the liquid and aqueous states-the ions are free to move

• Molecular compounds:� Do not conduct electricity in any state

� Molecules are comprised of uncharged particles

Electrical Conductivity

Your Turn!

Which of the following is likely true of NO2?

A. it conducts electricity well

B. It has a low melting point

C. It is likely a solid in its pure form

D. None of these

Ch 2. Elements, Compounds and Chemical Reactions Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 90 91 92 93...

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Transcript of Ch 2. Elements, Compounds and Chemical Reactions Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 90 91 92 93...