Chapter 8: ATOMIC ELECTRON CONFIGURATIONS AND PERIODICITY

1Chapter 8: ATOMIC ELECTRON Chapter 8: ATOMIC ELECTRON

CONFIGURATIONS AND CONFIGURATIONS AND PERIODICITYPERIODICITY

Chapter 8: ATOMIC ELECTRON Chapter 8: ATOMIC ELECTRON CONFIGURATIONS AND CONFIGURATIONS AND

PERIODICITYPERIODICITY

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Arrangement of Arrangement of Electrons in AtomsElectrons in Atoms


Electrons 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 no Each orbital can be assigned no

more than 2 electrons!more than 2 electrons!

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

quantum number, the quantum number, the electron electron

spin quantum number, mspin quantum number, mss..



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Electron Electron Spin Spin

Quantum Quantum Number, Number,

mmss

Can be proved experimentally that electronCan be proved experimentally that electronhas a spin. Two spin directions are given byhas a spin. Two spin directions are given bymmss where m where mss = +1/2 and -1/2. = +1/2 and -1/2.

Can be proved experimentally that electronCan be proved experimentally that electronhas a spin. Two spin directions are given byhas a spin. Two spin directions are given bymmss where m where mss = +1/2 and -1/2. = +1/2 and -1/2.

5Electron Spin Quantum Electron Spin Quantum NumberNumber

DiamagneticDiamagnetic: NOT attracted to a magnetic : NOT attracted to a magnetic fieldfieldParamagneticParamagnetic: substance is attracted to a : substance is attracted to a magnetic field. Substance has magnetic field. Substance has unpaired unpaired electronselectrons..

DiamagneticDiamagnetic: NOT attracted to a magnetic : NOT attracted to a magnetic fieldfieldParamagneticParamagnetic: substance is attracted to a : substance is attracted to a magnetic field. Substance has magnetic field. Substance has unpaired unpaired 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

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

QUANTUMQUANTUMNUMBERSNUMBERSQUANTUMQUANTUMNUMBERSNUMBERS

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Pauli Exclusion Pauli Exclusion PrinciplePrinciple

No two electrons in the No two electrons in the same atom can have the same atom can have the same set of 4 quantum same set of 4 quantum numbers.numbers.

That is, each electron in an That is, each electron in an atom has a unique address atom has a unique address of quantum numbers.of quantum numbers.

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Electrons in AtomsElectrons in AtomsElectrons in AtomsElectrons in Atoms

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

this shell has a single orbital (1s) to this 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 orbital 2s 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, 2



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


When n = 3, then l = 0, 1, 2When n = 3, then l = 0, 1, 2





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When n = 4, then l = 0, 1, 2, 3When n = 4, then l = 0, 1, 2, 3




seven 4f orbitalsseven 4f orbitals 14e-14e-


And many more!And many more!And many more!And many more!

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Assigning Electrons to Assigning Electrons to AtomsAtoms

Assigning Electrons to Assigning Electrons to AtomsAtoms

• Electrons generally assigned to orbitals of Electrons 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 depends For 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.

• Electrons generally assigned to orbitals of Electrons 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 depends For 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 Assigning Electrons to SubshellsSubshells

• In H atom all subshells of In H atom all subshells of same n have same same n have same energy.energy.

• In many-electron atom:In many-electron atom:a) subshells increase in a) subshells increase in

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

b) for subshells of same b) for subshells of same (n + l), the subshell with (n + l), the subshell with

lower n is lower in lower n is lower in energy.energy.

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Electron Electron Filling Filling OrderOrder

Figure 8.5Figure 8.5

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

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

• Z* is the nuclear charge experienced by Z* is the nuclear charge experienced by the outermost electrons.the outermost electrons.

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

• Z* increases across a period owing to Z* increases across a period owing to incomplete 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 Li Charge felt by 2s e- in Li Z* = 3 - 2 = 1 Z* = 3 - 2 = 1

• Be Be Z* = 4 - 2 = 2Z* = 4 - 2 = 2

• B B Z* = 5 - 2 = 3Z* = 5 - 2 = 3 and so on!and so on!

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Effective Effective Nuclear Nuclear ChargeCharge

Electron cloud for 1s electrons

Figure 8.6

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Writing Atomic Electron Writing Atomic Electron ConfigurationsConfigurations


11 s

value of nvalue of l

no. ofelectrons

spdf notationfor H, atomic number = 1

Two ways of Two ways of writing configs. writing configs. One is called One is called the the spdf spdf notation.notation.

Two ways of Two ways of writing configs. writing configs. One is called One is called the the spdf spdf notation.notation.

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Two ways of Two ways of writing writing configs. Other configs. Other is called the is called the orbital box orbital box notation.notation.

Two ways of Two ways of writing writing configs. Other configs. Other is called the is called the orbital box orbital box notation.notation.

Arrowsdepictelectronspin

ORBITAL BOX NOTATIONfor He, atomic number = 2

1s

21 s

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 in Valence Orbitals

• Li +1.28

• Be -------

• B +2.58

• C +3.22

• N +3.85

• O +4.49

• F +5.13

Increase in Increase in Z* across a Z* across a periodperiod

21General Periodic General Periodic TrendsTrends

• 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 Atomic SizeSize

Atomic Atomic SizeSize

• Size goes UPSize goes UP on going on going down a group.down a group.

• Because electrons are Because electrons are added farther from the added farther from the nucleus, there is less nucleus, there is less attraction.attraction.

• Size goes DOWNSize goes DOWN on going on going across a period.across a period.

• Size goes UPSize goes UP on going on going down a group.down a group.

• Because electrons are Because electrons are added farther from the added farther from the nucleus, there is less nucleus, there is less attraction.attraction.

• Size goes DOWNSize goes DOWN on going on going across a period.across a period.

23Atomic Atomic RadiiRadiiAtomic Atomic RadiiRadii


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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

NeAr

2nd period

3rd period 1st transitionseries

Radius (pm)

Atomic Number

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40

Li

Na

K

Kr

He

NeAr

2nd period

3rd period 1st transitionseries

Radius (pm)

Atomic Number

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Ion SizesIon SizesIon SizesIon Sizes

Li,152 pm3e and 3p

Li+, 60 pm2e and 3 p

+Does the size goDoes the size goup or down up or down when losing an when losing an electron to form electron to form a cation?a cation?

Does the size goDoes the size goup or down up or down when losing an when losing an electron to form electron to form a cation?a cation?

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• CATIONSCATIONS are are SMALLERSMALLER than the than the atoms from which they come.atoms from which they come.

• The electron/proton attraction has The electron/proton attraction has gone UP and so size gone UP and so size DECREASESDECREASES..

Li,152 pm3e and 3p

Li +, 78 pm2e and 3 p

+Forming Forming a cation.a cation.Forming Forming a cation.a cation.

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F,64 pm9e and 9p

F- , 136 pm10 e and 9 p

-Does the size go up or Does the size go up or down when gaining an down when gaining an electron to form an electron to form an anion?anion?

Does the size go up or Does the size go up or down when gaining an down when gaining an electron to form an electron to form an anion?anion?

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• ANIONSANIONS are are LARGERLARGER than the atoms from than the atoms from which they come.which they come.

• The electron/proton attraction has gone DOWN The electron/proton attraction has gone DOWN and so size and so size INCREASESINCREASES..

• Trends in ion sizes are the same as atom sizes. Trends in ion sizes are the same as atom sizes.

Forming Forming an anion.an anion.Forming Forming an anion.an anion.F, 71 pm

9e and 9pF-, 133 pm10 e and 9 p

-

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Trends in Ion SizesTrends in Ion SizesTrends in Ion SizesTrends in Ion Sizes


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Redox Reactions

Redox Reactions

Why do metals lose Why do metals lose

electrons in their electrons 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 take Why do nonmetals take

on electrons?on electrons?

Why do metals lose Why do metals lose

electrons in their electrons 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 take Why do nonmetals take

on electrons?on electrons?

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Ionization EnergyIonization EnergySee Screen 8.12See Screen 8.12


IE = energy required to remove an electron IE = 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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Mg (g) + 735 kJ ---> MgMg (g) + 735 kJ ---> Mg++ (g) + e- (g) + e-

MgMg+ + (g) + 1451 kJ ---> Mg(g) + 1451 kJ ---> Mg2+2+ (g) + e- (g) + e-

MgMg2+2+ (g) + 7733 kJ ---> Mg (g) + 7733 kJ ---> Mg3+3+ (g) + e- (g) + e-

Energy cost is very high to dip into a Energy cost is very high to dip into a shell of lower n. shell of lower n. This is why ox. no. = Group no.This is why ox. no. = Group no.



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Trends in Ionization EnergyTrends in Ionization EnergyTrends in Ionization EnergyTrends in Ionization Energy

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 350

500

1000

1500

2000

2500

1st Ionization energy (kJ/mol)

Atomic NumberH Li Na K

HeNe

ArKr

34Trends in Ionization Trends in Ionization

EnergyEnergyTrends in Ionization Trends in Ionization

EnergyEnergy

• IE increases across a period IE increases across a period because Z* increases.because Z* increases.

• Metals lose electrons more Metals lose electrons more easily than nonmetals.easily than nonmetals.

• Metals are good reducing Metals are good reducing agents.agents.

• Nonmetals lose electrons with Nonmetals lose electrons with difficulty.difficulty.

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Trends in Ionization Trends in Ionization EnergyEnergy

Trends in Ionization Trends in Ionization EnergyEnergy

• IE decreases down a group IE decreases down a group

• Because size increases.Because size increases.

• Reducing ability generally Reducing ability generally increases down the periodic increases 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 elements A few elements GAINGAIN electrons to electrons to form form anionsanions..

Electron affinity is the energy Electron affinity is the energy change 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 is E is EXOEXOthermic thermic because O has because O has an affinity for an an affinity for an e-.e-.

[He] O atom

EA = - 141 kJ

+ electron

O [He] - ion

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Electron Affinity of Electron Affinity of NitrogenNitrogen

∆∆E is E is zero zero for Nfor N- -

due to electron-due to electron-electron electron repulsions.repulsions.

EA = 0 kJ

[He] N atom

[He] N- ion

+ electron

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• Affinity for electron Affinity for electron increases across a increases across a period (EA becomes period (EA becomes more negative).more negative).

• Affinity decreases down Affinity decreases down a group (EA becomes a group (EA becomes less negative).less negative).

Atom EAAtom EAFF -328 kJ-328 kJClCl -349 kJ-349 kJBrBr -325 kJ-325 kJII -295 kJ-295 kJ

Atom EAAtom EAFF -328 kJ-328 kJClCl -349 kJ-349 kJBrBr -325 kJ-325 kJII -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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Chapter 8: ATOMIC ELECTRON CONFIGURATIONS AND PERIODICITY