22 November 2011

Take out your Problem Set (if you haven’t already handed it in)

Objective: You will be able to: describe, calculate and compare

the effective nuclear charge of elements

Agenda

I. Questions about electron configuration?

II. Effective nuclear charge notes and problems

Homework: Quiz Monday6-8 multiple choice, 2 multi-part free response

Periodic Properties of the Elements

Today

attraction between electrons and the nucleus

repulsion between electrons and some properties and their

trends on the periodic table that this attraction/repulsion causes

Effective Nuclear Charge First, some definitions:

force of attraction (between two charged particles) where Q1 and Q2 are the charges of the particles and d is the distance between them in general, electrons close to the nucleus will

be held with greater force than those that are more distant from the nucleus!

higher positive nuclear charges will draw electrons closer to the nucleus and hold them tighter.

221

dQkQF

Valence vs. Core Electrons

Valence electrons: electrons in the outermost orbitals of atoms, farthest from the nucleus

Core electrons: inner electrons, include electrons in completely full “d” orbitals

Effective Nuclear Charge

http://www.youtube.com/watch?v=MtP5mWLB-ys

Zeff, the net positive charge experienced by an electron in an atom.

Not the full nuclear charge because the core electrons “shield” (cancel) part of the positive nuclear charge.

Valence electrons experience less-than-full pull from the nuclear charge.

Shielding Effect

the reduction of the full nuclear charge experienced by an outer electron as a result of screening (cancelling) by inner core electrons

Trends in Effective Nuclear Charge

Zeff increases from left to right across any period core electrons maintain constant

across any row, but the nuclear charge increases, so Zeff increases

Zeff = Z – S S: screening constant, about equal

to the number of core electrons in an atom

Examples

Zeff is constant going down a group because valence electrons going down a group are constant, but there is an increase in number of protons to balance this

Problems

1. What is the approximate Zeff of scandium?

2. Are the valence electrons of Sc held more or less tightly than those of K?

Use scandium’s electron configuration to explain your answer.

Zeff produces trends…

Sizes of atoms and ions Ionization energy Electron affinity (electronegativity)

29 November 2011

Objective: You will be able to: describe trends on the periodic table caused by effective nuclear charge.

Do now: (On page 5, 3rd slide): How many energy levels do the

following atoms have?a. sodium b. potassium c.

rubidium Calculate Zeff for Na, Mg and Al.

Sizes of Atoms and Ions

atomic radius: an estimate of the size of an atom atoms don’t have sharply defined

boundaries because orbitals are areas of probability, so definite sizes can’t be determined

Atomic radius increases

Atomic radius increases

Atomic Radius (size of the atom)

Atomic Radius

Increases top to bottom: outer electrons are on higher energy levels, which are further from the nucleus

Decreases left to right: shielding remains constant as nuclear charge increases no more core electrons are added, but

more protons are, which pull the valence electrons closer to the nucleus

Ionic Radius

http://www.youtube.com/watch?v=hkyxQjKwBU4

Cations (+) are smaller than their parent atoms because the electron is lost from the valence shell, and e--e-

repulsions are decreased Anions (-) are larger than their parent

atoms because additional electrons cause increased e--e- repulsions, causing the electrons to spread out more in space

Ionization Energy

first ionization energy (I1): the energy required to remove the outermost electron from the ground state of a gaseous atom.

Ex: 495 kJ + Na(g) → Na+(g) + e−

second ionization energy (I2): the energy required to remove the second electron

etc. I1<I2<I3 because with each successive

removal, an electron is pulled away from an increasingly positive ion.

http://www.youtube.com/watch?v=6e4uoWQeM4s&feature=related

Ionization Energy IncreasesIo

niza

tion

Ene

rgy

Incr

ease

s

Exceptions

I1 decreases from Be to B and Mg to Al electrons in filled s or d orbitals

provide limited screening for electrons in p subshells

I1 decreases from N to O, P to S and As to Se due to repulsion of paired

electrons in the p4 configuration of group 16 atoms

Noble Gases

have the highest ionization energies of their periods because their valence electrons are poorly screened. very high Zeff

They are also the smallest in their periods

Problem

Arrange the period 3 elements in order of increasing first ionization energy, lowest to highest. Note any anomalies.

Electron Affinity

a.k.a. electronegativity ∆Hea, the energy change when an

electron is added to a gaseous atom F(g) + e- → F-(g) ∆Hea = -328 kJ/mol Energy is released when an atom

attracts an electron. http://www.youtube.com/watch?v=sc

vNYZD3jrI

Electronegativity IncreasesEl

ectr

oneg

ativ

ity

Incr

ease

s

Trend in Electron Affinity

Increases from left to right along a period

Increases from bottom to top within a group smaller atoms are less shielded and

attract electrons more easily Exception: F has less electron affinity

than chlorine because of the small size of F causes greater e--e- repulsion

Summary of Exceptions

Periodic Property

Periodic Anomaly

Explanation

Atomic radius noneFirst ionization energy

B<Be, Al<Mg Partial shielding by s valence electrons decreases Zeff

First ionization energy

O<N, S<P, Se<As, Te<Sb

Electron-electron repulsion in p4 configurations of Group 16 atoms

Electron affinity F<Cl Small size of fluorine contributes to strong electron-electron repulsion

30 November 2011

Objective: You will be able to describe and write chemical questions for patterns in reactivity on the periodic table.

Homework quiz (week of Nov. 28) Compare the radius and ionization

energy of oxygen and sulfur. Explain your answer.

Agenda

I. Homework QuizII. Homework answersIII. More trends on the periodic table:

reactivity and compounds formedHomework: Read lab – be familiar

with the procedure for tomorrow!p. 359 #61, 72, 73, 74, 82, 86, 95:

Mon.

Metals, Non-Metals, Metaloids

Metals: low ionization energy, lose electrons readily have luster, conduct heat and electricity,

malleable, ductile Metallic character increases right to left

along a period and top to bottom within a group

Metal hydrides, oxides and nitrides are basic Li2O(s) + H2O(l) → 2Li+(aq) + 2OH-(aq)

Non-metals have high electron affinity and gain electrons readily form negative ions do not have luster, and are poor

conductors of heat and electricity form molecular compounds non-metal oxides are acidic

SO2(g) + H2O(l) → H2SO3(aq)

metalloids have properties intermediate between those of metals and non-metals

Trends for Group 1 and 2 Metals

Group 1 alkali metals (group 1): soft, metallic

solids s1 valence electron configurations lose one electron to form 1+ cations become more reactive moving down

the group http://www.youtube.com/watch?v=ui

xxJtJPVXk

Alkali metal + Water

all alkali metals react with water to produce hydrogen gas

2Na(s) + 2H2O(l) → 2Na+(aq) + 2OH-(aq) + H2(g)

Alkali metal + H2 gas

all alkali metals react with hydrogen gas to form hydrides

2Li(s) + H2(g) → 2LiH(s)

Alkali metals + Non-metals

all alkali metals react with most non-metals

2K(s) + S(s) → K2S(s) 6Li(s) + N2(g) → 2Li3N(s)

Forming Peroxides

Na, K, Rb and Cs form peroxides 2Na(s) + O2(g) → Na2O2(s)

oxide ion: O2-

peroxide ion: O22-

superoxide ion: O2-

Forming Superoxides

K, Rb and Cs form superoxides K(s) + O2(g) → KO2(s)

When burned

Li: crimson-red Na: yellow K: violet

Practice

a. Write and balance a chemical equation to describe what happens when solid potassium is added to water.

b. Classify as acid-base, redox, or precipitation reaction.

c. Describe what you would observe when the reaction takes place.

6 December 2011

Objective: You will be able to: Describe trends in alkaline earth

metals, some non-metals, allotropes, halogens and noble gases

Do now: Find the final mass of your copper + filter paper.

Agenda

I. Do nowII. Trends in alkaline earth metals,

some non-metals, allotropes, halogens and noble gases

Homework: problem set due MondayQuiz Monday, Lab notebook due

monday

Alkaline Earth Metals (Group 2)

s2 valence electron configuration lose 2 electrons to make 2+ cations low ionization energy (but higher

than corresponding alkali metal) less reactive than alkali metals, but

are more reactive moving down the group

http://www.youtube.com/watch?v=kNA2ZDonFmE

http://www.youtube.com/watch?v=pPnnXD_K0BU

http://www.youtube.com/watch?v=QhYpEY2A1hg&feature=related

Reaction with H2O

Mg reacts with steam Mg(s) + 2H2O(g) → H2(g) + MgO(s)

Ca, Sr, Ba and Ra react with liquid water:

Ca(s) + H2O(l) → H2(g) + Ca2+(aq) + 2OH-(aq)

Reaction with O2(g)

Mg and Ca form oxides: 2Ca(s) + O2(g) → 2CaO(s)

http://www.youtube.com/watch?v=m2i9jLPXprQ

Reaction with Non-metals

3Mg(s) + N2(g) → Mg3N2(s)

When burned

Ca: brick red Sr: crimson red Ba: green-yellow http://www.youtube.com/watch?v=d

8hpUtRnsYc

Practice

a. Write and balance a chemical equation to describe what happens when solid calcium oxide is added to water.

b. Classify as acid-base, redox, or precipitation.

c. What color would a drop of phenolphthalein turn? Why?

Trends for Some Non-Metals

Hydrogen: 1s1 configuration puts it in group 1, BUT it doesn’t really belong in any group.

Extremely high ionization energy – no shielding

Can share electrons, so it is classified as a non-metal

Allotropes

Allotropes: different forms of the same element in the same state Carbon: C(s, graphite), C(s,

diamond) Phosphorus: P4(s, white), P(s, red) Oxygen: O2(g), O3(g) ozone Sulfur: S(s), S8(s)

Halogens (Group 17)

diatomic molecules: F2(g), Cl2(g), Br2(l), I2(s)

s2p5 valence electron configuration gain one electron to form 1- ion http://www.youtube.com/watch?v=y

P0U5rGWqdg

Noble Gases (Group 18)

nonmetallic, monatomic gases at room temperature

completely filled s and p sublevels form a limited number of

compounds: XeF2, XeF4, XeF6, KrF2, HArF

http://www.youtube.com/watch?v=HGUyH6zG7_U&feature=related

Homework

p.

1 December 2011

Objective: You will be able to: write and balance equations for

the reaction of copper through a series of reactions.

Do now: Grab a pair of goggles and sit next to your lab partner.

Copper cycle lab

Overview Location of reagents

fume hood Please leave reagents IN the fume

hood. Conduct the reaction with HNO3

in the fume hood until brown gas dissipates completely.

Reagents

Measure 2 mL nitric acid using the transfer pipette 2 times.

Use a graduated cylinderfor other reagents. Use the graduated cylinders only aslabeled to avoid cross-contamination! Use distilled water from your wash bottle

1 mL mark

Today

Complete this procedure through the set up for step 14

Your solution should be slowly reacting with the aluminum. Label this beaker and set it at the

back of your lab bench You should have a filtration setup

with a massed filter paper ready for Monday.

A few notes

Use a professional, quiet tone of voice

Avoid unnecessary movement around the room and unnecessary discussion with people across the room

Work carefully on your lab notebook, making qualitative observations and recording each reaction. Find a neat way to organize and label data!

5 December 2011

Objective: You will be able to: write and balance equations for

the reaction of copper through a series of reactions.

Do now: Grab a pair of goggles and your beaker, and sit down next to your lab partner silently.

Observations?

Today’s goals

1. Record observations2. Mass filter paper and initial it3. Filter solution, picking out unreacted Al4. Place filter paper on a watch glass in

the drying oven5. Finish writing and balancing molecular

and net ionic equations6. Lab notebooks due Monday (we’ll find

final mass tomorrow)

Homework

p. 359 #61, 72, 73, 74, 82, 86, 95: Tuesday

8 December 2011

Objective: You will be able to: write and balance molecular and

net ionic equations review periodic properties of the

elements

Your options

a. Work with a partner on the problem set

b. Work with your lab partner to complete the copper cycle lab

Both are due MondayQuiz on The Periodic Properties of the

Elements Monday

Criteria for your work

Work with 1 or 2 individuals Sit at a table with only those

individuals Use a tone and volume of voice

appropriate to the situation and environment

Be equally engaged in your work Work consistently and efficiently for

the length of the class