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8/14/2019 chemical begins

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Chapter 8: ATOMIC ELECTRONChapter 8: ATOMIC ELECTRONCONFIGURATIONS ANDCONFIGURATIONS AND

PERIODICITYPERIODICITY


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Arrangement ofArrangement of

Electrons in AtomsElectrons in AtomsElectrons in atoms are arranged asElectrons in atoms are arranged as

SHELLSSHELLS (n)(n)

SUBSHELLSSUBSHELLS (l)(l)

ORBITALSORBITALS (m(mll))


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Each orbital can be assigned noEach orbital can be assigned no

more than 2 electrons!more than 2 electrons!

This is tied to the existence of a 4thThis is tied to the existence of a 4th

quantum number, thequantum number, the electronelectron

spin quantum number, mspin quantum number, mss..

Arrangement ofArrangement of

Electrons in AtomsElectrons in Atoms


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ElectronElectronSpinSpin

QuantumQuantumNumber,Number,

mmss

Can be proved experimentally that electronCan be proved experimentally that electron

has a spin. Two spin directions are given byhas a spin. Two spin directions are given by

mmss where mwhere mss = +1/2 and -1/2.= +1/2 and -1/2.


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Electron Spin Quantum NumberElectron Spin Quantum Number

DiamagneticDiamagnetic: NOT attracted to a magnetic: NOT attracted to a magnetic

fieldfieldParamagneticParamagnetic: substance is attracted to a: substance is attracted to amagnetic field. Substance hasmagnetic field. Substance has unpairedunpaired

electronselectrons..


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n ---> shelln ---> shell 1, 2, 3, 4, ...1, 2, 3, 4, ...

l ---> subshelll ---> subshell 0, 1, 2, ... n - 10, 1, 2, ... n - 1

mmll ---> orbital---> orbital -l ... 0 ... +l-l ... 0 ... +l

mmss ---> electron spin---> electron spin +1/2 and -1/2+1/2 and -1/2

QUANTUMQUANTUMNUMBERSNUMBERS


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Pauli Exclusion PrinciplePauli Exclusion PrincipleNo two electrons in theNo two electrons in the

same atom can have thesame atom can have thesame set of 4 quantumsame set of 4 quantumnumbers.numbers.

That is, each electron in anThat is, each electron in anatom has a unique addressatom has a unique addressof quantum numbers.of quantum numbers.


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When n = 1, then l = 0When n = 1, then l = 0

this shell has a single orbital (1s) tothis shell has a single orbital (1s) to

which 2e- can be assigned.which 2e- can be assigned.

When n = 2, then l = 0, 1When n = 2, then l = 0, 1

2s orbital2s orbital 2e-2e-

three 2p orbitalsthree 2p orbitals 6e-6e- TOTAL =TOTAL = 8e-8e-


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When n = 3, then l = 0, 1, 2When n = 3, then l = 0, 1, 23s orbital3s orbital 2e-2e-

three 3p orbitalsthree 3p orbitals 6e-6e-

five 3d orbitalsfive 3d orbitals 10e-10e-

TOTAL =TOTAL = 18e-18e-


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When n = 4, then l = 0, 1, 2, 3When n = 4, then l = 0, 1, 2, 34s orbital4s orbital 2e-2e-

three 4p orbitalsthree 4p orbitals 6e-6e-

five 4d orbitalsfive 4d orbitals 10e-10e-seven 4f orbitalsseven 4f orbitals 14e-14e-

TOTAL =TOTAL = 32e-32e-

And many more!And many more!


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Assigning Electrons to AtomsAssigning Electrons to Atoms

Electrons generally assigned to orbitals ofElectrons generally assigned to orbitals of

successively higher energy.successively higher energy.

For H atoms, E = - C(1/nFor H atoms, E = - C(1/n22). E depends only). E depends only

on n.on n.

For many-electron atoms, energy dependsFor many-electron atoms, energy depends

on both n and l.on both n and l.

See Figure 8.5, page 295 and Screen 8. 7.See Figure 8.5, page 295 and Screen 8. 7.


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Assigning Electrons to SubshellsAssigning Electrons to Subshells In H atom all subshells ofIn H atom all subshells of

same n have samesame n have sameenergy.energy.

In many-electron atom:In many-electron atom:

a) subshells increase ina) subshells increase in

energy as value of (n + l)energy as value of (n + l)increases.increases.

b) for subshells of sameb) for subshells of same

(n + l), the subshell with(n + l), the subshell withlower n is lower inlower n is lower inenergy.energy.


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ElectronElectronFillingFilling

OrderOrderFigure 8.5Figure 8.5


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Effective Nuclear Charge, Z*Effective Nuclear Charge, Z*

Z* is the nuclear charge experienced byZ* is the nuclear charge experienced bythe outermost electrons.the outermost electrons.

Explains why E(2s) < E(2p)Explains why E(2s) < E(2p)

Z* increases across a period owing toZ* increases across a period owing toincomplete shielding by inner electrons.incomplete shielding by inner electrons.

Estimate Z* by --> [Estimate Z* by --> [ Z - (no. inner electrons)Z - (no. inner electrons) ]]

Charge felt by 2s e- in LiCharge felt by 2s e- in Li Z* = 3 - 2 = 1Z* = 3 - 2 = 1

BeBe Z* = 4 - 2 = 2Z* = 4 - 2 = 2

BB Z* = 5 - 2 = 3Z* = 5 - 2 = 3 and so on!and so on!


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EffectiveEffectiveNuclearNuclear

ChargeCharge

Electron cloud

for 1s electrons

Figure 8.6


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Writing Atomic ElectronWriting Atomic Electron

ConfigurationsConfigurations

11 s

value of nvalue of l

no. ofelectrons

spdf notationfor H, atomic number = 1

Two ways ofTwo ways ofwriting configs.writing configs.One is calledOne is called

thethe spdfspdfnotation.notation.


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Writing Atomic ElectronWriting Atomic ElectronConfigurationsConfigurations

Two ways ofTwo ways ofwritingwritingconfigs. Otherconfigs. Other

is called theis called theorbital boxorbital boxnotation.notation.

Arrowsdepictelectronspin

ORBITAL BOX NOTATIONfor He, atomic number = 2

1s

21 s

One electron has n = 1, l = 0, mOne electron has n = 1, l = 0, m ll = 0, m= 0, mss = + 1/2= + 1/2

Other electron has n = 1, l = 0, mOther electron has n = 1, l = 0, m ll = 0, m= 0, mss = - 1/2= - 1/2


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See Toolbox for Electron Configuration tool.See Toolbox for Electron Configuration tool.


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EffectiveEffective Nuclear Charge, Z*Nuclear Charge, Z*

Atom Z* Experienced by Electrons inValence Orbitals

Li +1.28

Be -------

B +2.58 C +3.22

N +3.85

O +4.49

F +5.13

Increase inIncrease inZ* across aZ* across a

periodperiod


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General Periodic TrendsGeneral Periodic Trends Atomic and ionic sizeAtomic and ionic size

Ionization energyIonization energy

Electron affinityElectron affinity

Higher effective nuclear charge.Electrons held more tightly

Smaller orbitals.Electrons held moretightly.


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Atomic SizeAtomic Size

Size goes UPSize goes UP on goingon goingdown a group.down a group.

Because electrons areBecause electrons areadded farther from theadded farther from thenucleus, there is lessnucleus, there is less

attraction.attraction. Size goes DOWNSize goes DOWN on goingon going

across a period.across a period.


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Figure 8.9Figure 8.9


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Trends in Atomic SizeTrends in Atomic SizeSee Figures 8.9 & 8.10See Figures 8.9 & 8.10

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40

Li

Na

K

Kr

He

Ne

Ar

2nd period

3rd period 1st transition

series

Radius (pm)

Atomic Number


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Ion SizesIon Sizes

Li,152 pm3e and 3p

Li+, 60 pm2e and 3 p

+Does the sizeDoes the sizegogo

up or downup or down

when losing anwhen losing anelectron to formelectron to form

a cation?a cation?


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Ion SizesIon Sizes

CATIONSCATIONS areare SMALLERSMALLER than thethan theatoms from which they come.atoms from which they come.

The electron/proton attractionThe electron/proton attractionhas gone UP and so sizehas gone UP and so sizeDECREASESDECREASES..

Li,152 pm3e and 3p

Li +, 78 pm2e and 3 p

+FormingForming

a cation.a cation.


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Ion SizesIon Sizes

F,64 pm9e and 9p

F- , 136 pm10 e and 9 p

-Does the size go up orDoes the size go up ordown when gaining andown when gaining anelectron to form anelectron to form ananion?anion?


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Ion SizesIon Sizes

ANIONSANIONS areare LARGERLARGER than the atomsthan the atomsfrom which they come.from which they come.

The electron/proton attraction hasThe electron/proton attraction has

gone DOWN and so sizegone DOWN and so size INCREASESINCREASES.. Trends in ion sizes are the same asTrends in ion sizes are the same as

atom sizes.atom sizes.

FormingForming

an anion.an anion.F, 71 pm9e and 9p

F-, 133 pm10 e and 9 p

-


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Trends in Ion SizesTrends in Ion Sizes

Figure 8.13Figure 8.13

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Redox Reactions

Why do metals loseWhy do metals lose

electrons in theirelectrons in their

reactions?reactions?

Why does Mg form MgWhy does Mg form Mg2+2+

ions and not Mgions and not Mg3+3+??

Why do nonmetals takeWhy do nonmetals takeon electrons?on electrons?

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Ionization EnergyIonization EnergySee Screen 8.12See Screen 8.12

IE = energy required to remove an electronIE = energy required to remove an electron

from an atom in the gas phase.from an atom in the gas phase.

Mg (g) + 738 kJ ---> MgMg (g) + 738 kJ ---> Mg++

(g) + e-(g) + e-


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Trends in Ionization EnergyTrends in Ionization Energy

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35

0

500

1000

1500

2000

2500

1st Ionization energy (kJ/mol)

Atomic NumberH Li Na K

HeNe

Ar

Kr

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IE increases across a periodIE increases across a periodbecause Z* increases.because Z* increases.

Metals lose electrons moreMetals lose electrons more

easily than nonmetals.easily than nonmetals.

Metals are good reducingMetals are good reducing

agents.agents.

Nonmetals lose electrons withNonmetals lose electrons withdifficulty.difficulty.

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IE decreases down a groupIE decreases down a group

Because size increases.Because size increases.

Reducing ability generallyReducing ability generally

increases down the periodicincreases down the periodic

table.table.

See reactions of Li, Na, KSee reactions of Li, Na, K

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Electron AffinityElectron Affinity

A few elementsA few elements GAINGAIN electrons toelectrons toformform anionsanions..

Electron affinity is the energyElectron affinity is the energychange when an electron is added:change when an electron is added:

A(g) + e- ---> AA(g) + e- ---> A--(g) E.A. = E(g) E.A. = E

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Electron Affinity of OxygenElectron Affinity of Oxygen

E isE is EXOEXOthermicthermicbecause O hasbecause O has

an affinity for anan affinity for ane-.e-.

[He] O atom

EA = - 141 kJ

+ electron

O [He] - ion

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Electron Affinity of NitrogenElectron Affinity of Nitrogen

E isE is zerozero for Nfor N--

due to electron-due to electron-

electronelectronrepulsions.repulsions.

EA = 0 kJ

[He] N atom

[He] N- ion + electron

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Affinity for electronAffinity for electronincreases across aincreases across a

period (EA becomesperiod (EA becomesmore negative).more negative).

Affinity decreases downAffinity decreases downa group (EA becomesa group (EA becomes

less negative).less negative).

Atom EAAtom EA

FF -328 kJ-328 kJ

ClCl -349 kJ-349 kJBrBr -325 kJ-325 kJ

II -295 kJ-295 kJ

Trends in Electron AffinityTrends in Electron Affinity

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Trends in Electron AffinityTrends in Electron Affinity

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