Chapter 8 Atomic Electron Configurations and Chemical Periodicity.

Chapter 8Chapter 8

Atomic Electron Configurations Atomic Electron Configurations and Chemical Periodicityand Chemical Periodicity

Chapter goalsChapter goals

• Understanding the role magnetism Understanding the role magnetism plays in determining and revealing plays in determining and revealing atomic structure.atomic structure.

• Understand effective nuclear charge Understand effective nuclear charge and its role in determining atomic and its role in determining atomic properties.properties.

• Write the electron configuration of Write the electron configuration of neutral atoms and monatomic ions.neutral atoms and monatomic ions.

• Understand the fundamental physical Understand the fundamental physical properties of the elements and their properties of the elements and their periodic trends.periodic trends.

Electron Spin Electron Spin and the Fourth Quantum Numberand the Fourth Quantum Number

• The fourth quantum number is the spin quantum The fourth quantum number is the spin quantum number which has the symbol mnumber which has the symbol mss..

• The spin quantum number only has two possible The spin quantum number only has two possible values.values.

mms s = +1/2 or = +1/2 or −−1/21/2

mmss = ± 1/2 = ± 1/2• This quantum number tells us the spin and This quantum number tells us the spin and

orientation of the magnetic field of the electrons.orientation of the magnetic field of the electrons.• Wolfgang Pauli discovered the Exclusion Wolfgang Pauli discovered the Exclusion

Principle in 1925.Principle in 1925.No two electrons in an atom can have the same No two electrons in an atom can have the same

set of 4 quantum numbers, n, set of 4 quantum numbers, n, ll, m, mll, and m, and mss

Electron Spin Electron Spin

• Spin quantum number effects:Spin quantum number effects:– Every orbital can hold up to two Every orbital can hold up to two

electrons.electrons.• Consequence of the Pauli Exclusion Consequence of the Pauli Exclusion

Principle.Principle.– The two electrons are designated as The two electrons are designated as

havinghaving– one spin up one spin up m mss = +1/2 = +1/2– and one spin downand one spin downmmss = = −−1/21/2

• Spin describes the direction of the Spin describes the direction of the electron’s magnetic field.electron’s magnetic field.

Paramagnetism and DiamagnetismParamagnetism and Diamagnetism

• Unpaired electrons have their spins Unpaired electrons have their spins aligned aligned or or (in diff. (in diff. orbitals)orbitals)

– This increases the magnetic field of the This increases the magnetic field of the atom.atom.

Total spin Total spin 0, because they add up. 0, because they add up.

• Atoms with unpaired electrons are called Atoms with unpaired electrons are called paramagneticparamagnetic ..

– Paramagnetic atoms are attracted to a Paramagnetic atoms are attracted to a magnet.magnet.

Paramagnetism and DiamagnetismParamagnetism and Diamagnetism• Paired electrons have their spins Paired electrons have their spins

unaligned unaligned in the same orbitalin the same orbital– Paired electrons have no net magnetic Paired electrons have no net magnetic

field.field. Total spin = 0, because of cancellation,Total spin = 0, because of cancellation, ½ ½ −− ½ = 0 ½ = 0

• Atoms with no unpaired electrons are Atoms with no unpaired electrons are called called diamagneticdiamagnetic. . – Diamagnetic atoms are not attracted to a Diamagnetic atoms are not attracted to a

magnet.magnet.

Atomic Orbitals, Spin, and # of ElectronsAtomic Orbitals, Spin, and # of Electrons

• Because two electrons in the same orbital Because two electrons in the same orbital must be paired (due to Pauli’s Exclusion must be paired (due to Pauli’s Exclusion Principle), it is possible to calculate the Principle), it is possible to calculate the number of orbitals and the number of number of orbitals and the number of electrons in each n shell. electrons in each n shell.

• The number of orbitals per n level is given The number of orbitals per n level is given by nby n2 2 (see table at end of chapter 7.)(see table at end of chapter 7.)

• The maximum number of electrons per n The maximum number of electrons per n level is 2nlevel is 2n22 (two electrons per orbital.) (two electrons per orbital.)

– The value is 2nThe value is 2n22 because of the two because of the two paired electrons per orbital.paired electrons per orbital.

nn shellshell ll subshellsubshell mmll

#orbitals#orbitals#e#e––

11 KK 00 ss 00 11 2222 LL 00 ss 00 11 22

11 pp ––1,0,11,0,1 33 6633 MM 00 ss 00 11 22

11 pp ––1,0,11,0,1 33 66

88

22 dd -2,-1,0,1,2-2,-1,0,1,2 55 10101818

44 NN 00 ss 00 11 2211 pp ––1,0,11,0,1 33 6622 dd -2,-1,0,1,2-2,-1,0,1,2 55 101033 ff -3,-2,-1,0,1,2,3-3,-2,-1,0,1,2,3 77 1414

3232

n2

1

4

9

16

Max

Atomic Subshell Energies and Atomic Subshell Energies and Electron AssignmentsElectron Assignments

• The principle that describes how the The principle that describes how the periodic chart is a function of electronic periodic chart is a function of electronic configurations is the configurations is the Aufbau PrincipleAufbau Principle..

• The electron that distinguishes an element The electron that distinguishes an element from the previous element enters the from the previous element enters the lowest energy atomic orbital available.lowest energy atomic orbital available.

Penetrating and ShieldingPenetrating and Shielding• the radial distribution function the radial distribution function

shows that the 2shows that the 2ss orbital orbital penetrates more deeply into the penetrates more deeply into the 11ss orbital than does the 2 orbital than does the 2pp

• the weaker penetration of the 2the weaker penetration of the 2pp sublevel means that electrons in sublevel means that electrons in the 2the 2pp sublevel experience more sublevel experience more repulsive force, they are more repulsive force, they are more shielded from the attractive force shielded from the attractive force of the nucleusof the nucleus

• the deeper penetration of the 2the deeper penetration of the 2ss electrons means electrons in the electrons means electrons in the 22ss sublevel experience a greater sublevel experience a greater attractive force to the nucleus and attractive force to the nucleus and are not shielded as effectivelyare not shielded as effectively

• the result is that the electrons in the result is that the electrons in the 2the 2ss sublevel are lower in ( sublevel are lower in (more more negativenegative) energy than the ) energy than the electrons in the 2electrons in the 2pp

Atomic Subshell Energies and Electron Atomic Subshell Energies and Electron AssignmentsAssignments

The The Aufbau PrincipleAufbau Principle

describes the electron describes the electron

filling order in atoms. Thisfilling order in atoms. This

is product of the effective is product of the effective

nuclear charge, Z*, nuclear charge, Z*, ZZeffeff

For the same n, Z* is higherFor the same n, Z* is higher

for s orbital: s > p > d > f for s orbital: s > p > d > f

Then, eThen, e−− in s is the most in s is the most

attracted by nucleus and hasattracted by nucleus and has

the lowest energythe lowest energy


One mnemonic One mnemonic

to remember theto remember the

correct filling correct filling

order for order for

electrons electrons

in atoms is the in atoms is the

increasing increasing

(n + (n + ) value


or we can use this periodic chart or we can use this periodic chart

Atomic Electron ConfigurationsAtomic Electron Configurations

• Now we will use the Aufbau Principle to Now we will use the Aufbau Principle to determine the electronic configurations of determine the electronic configurations of the elements on the periodic chart.the elements on the periodic chart.

• 11stst row elements row elements

22

11

1s He

1s H

ionConfigurat 1s

Atomic Electron ConfigurationsAtomic Electron ConfigurationsHund’s rule tells us that the electrons will fill the p and d orbitals

by placing electrons in each orbital singly and with same spin until half-filled. That is the rule of maximum spin. Then the electrons will pair to finish the p orbitals.

Electrons in orbitals of or same kind, such as p or d orbitals, in the sameshell (n), have the same energy; theare said to bedegenerate.

Atomic Electron ConfigurationsAtomic Electron Configurations3rd row elements…

62

18

5217

4216

3215

2214

1213

212

111

3p s3 Ne NeAr

3p s3 Ne Ne Cl

3p s3 Ne Ne S

3p s3 Ne Ne P

3p s3 Ne Ne Si

3p s3 Ne Ne Al

s3 Ne Ne Mg

s3 Ne NeNa

ionConfigurat 3p 3s

Atomic Electron ConfigurationsAtomic Electron Configurations4th row elements…

119 4s Ar ArK

ionConfigurat 4p 4s 3d


2

20

119

4s Ar ArCa

4s Ar ArK


Atomic Electron ConfigurationsAtomic Electron Configurations4th row elements…The five d orbitals are degenerate

12

21

220

119

3d 4s Ar Ar Sc

4s Ar ArCa

4s Ar ArK



22

22

1221

220

119

3d 4s Ar Ar Ti

3d 4s Ar Ar Sc

4s Ar ArCa

4s Ar ArK


Atomic Electron ConfigurationsAtomic Electron Configurations4th row elements…The five d orbitals are degenerate

3223

2222

1221

220

119

3d 4s Ar Ar V

3d 4s Ar Ar Ti

3d 4s Ar Ar Sc

4s Ar ArCa

4s Ar ArK



3223

2222

1221

220

119

3d 4s Ar Ar V

3d 4s Ar Ar Ti

3d 4s Ar Ar Sc

4s Ar ArCa

4s Ar ArK


Atomic Electron ConfigurationsAtomic Electron Configurations4th row elements… The [Ar] 4s1 3d5 configuration of

Cr is more stable than [Ar] 4s2 3d4 (expected)

orbitals. filled completely and filled-half with

associatedstability of measure extraan is There

3d 4s Ar ArCr

3d 4s Ar Ar V

3d 4s Ar Ar Ti

3d 4s Ar Ar Sc

4s Ar Ar Ca

4s Ar ArK


5124

3223

2222

1221

220

119

Atomic Electron ConfigurationsAtomic Electron Configurations4th row elements… The [Ar] 4s1 3d10 full d configuration

of Cu is more stable than [Ar] 4s2 3d9 (expected)

reason. same y theessentiallfor

andCr like exceptionAnother

3d 4s Ar Ar Cu

3d 4s Ar Ar Ni

3d 4s Ar Ar Co

3d 4s Ar Ar Fe

3d 4s Ar Ar Mn


10129

8228

7227

6226

5225


102

30

10129

8228

7227

6226

5225

3d 4s Ar Ar Zn

3d 4s Ar Ar Cu

3d 4s Ar Ar Ni

3d 4s Ar Ar Co

3d 4s Ar Ar Fe

3d 4s Ar Ar Mn


Atomic Electron ConfigurationsAtomic Electron Configurations4th row elements… (remember Hund’s rule):

__ is better (lower energy) than __ __

4p 4p

6102

36

510235

410234

310233

210232

110231

4p 3d 4s Ar ArKr

4p 3d 4s Ar ArBr

4p 3d 4s Ar Ar Se

4p 3d 4s Ar Ar As

4p 3d 4s Ar Ar Ge

4p 3d 4s Ar ArGa


Atomic Electron ConfigurationsAtomic Electron ConfigurationsLanthanides (4f)

56Ba [Xe] 6s2

57La [Xe] 5d1 6s2

58Ce [Xe] 4f1 5d1 6s2

59Pr [Xe] 4f3 6s2 Praseodymium

70Yb [Xe] 4f14 6s2 Ytterbium

71Lu [Xe] 4f14 5d1 6s2 Lutetium

Periodic TablePeriodic Table

s, p, d, and f-block in the Periodic Tables, p, d, and f-block in the Periodic Table

GaGa3131

InIn4949

TlTl8181

BB55

AlAl1313

3A3A

GeGe3232

SnSn5050

PbPb8282

CC66

SiSi1414

4A4A

AsAs3333

SbSb5151

BiBi8383

NN77

PP1515

5A5A

SeSe3434

TeTe5252

PoPo8484

OO88

SS1616

6A6A

BrBr3535

II5353

AtAt8585

FF99

ClCl1717

7A7A

KrKr3636

XeXe5454

RnRn8686

NeNe1010

ArAr1818

HeHe228A8A

ZnZn

CeCe5858

PrPr5959

NdNd6060

PmPm6161

SmSm6262

EuEu6363

GdGd6464

TbTb6565

DyDy6666

HoHo6767

ErEr6868

TmTm6969

YbYb7070

LuLu7171

ThTh9090

PaPa9191

UU9292

NpNp9393

PuPu9494

AmAm9595

CmCm9696

BkBk9797

CfCf9898

EsEs9999

FmFm100100

MdMd101101

NoNo102102

LrLr103103

BaBa5656

BeBe44

MgMg

1212

CaCa

2020

SrSr

3838

RaRa8888

2A2A

1A1A

HH11

LiLi33

NaNa

1111

KK

1919

RbRb

3737

CsCs5555

FrFr8787

AcAc RfRf DbDb SgSg BhBh HsHs MtMt

HgHgLaLa5757

ScSc

2121

YY

3939

8989

3B3B

TiTi

2222

ZrZr4040

HfHf7272

104104

4B4B

VV

2323

NbNb4141

TaTa7373

105105

5B5B

CrCr2424

MoMo4242

WW7474

106106

6B6B

MnMn

TcTc

ReRe

2525

4343

7575

107107

7B7B

FeFe

OsOs

2626

RuRu4444

7676

108108

8B8B

IrIr

4545

7777

CoCo2727

RhRh

109109

8B8B

NiNi2828

PdPd

4646

PtPt7878

8B8B

CuCu2929

AgAg4747

AuAu7979

1B1B3030

CdCd4848

8080

2B2B

11

22

33

44

55

66

77

(P–1)d(P–1)d

(P)s(P)s

(P–2)f(P–2)f

(P)p(P)p

PP

Valence ElectronsValence Electronselectrons in shell with highest electrons in shell with highest nn, i.e., , i.e., the outermost the outermost

electronselectrons, those beyond the core electrons, those beyond the core electrons

1s1s22 2s 2s2 2 2p2p66 3s3s11

1s1s22 2s 2s2 2 2p2p66 3s3s22 3p 3p22

1s1s22 2s 2s2 2 2p2p66 3s 3s22 3p 3p66 3d 3d1010 4s4s22 4p 4p66

1s1s22 2s2s2 2

1s1s22 2s 2s2 2 2p2p66 3s3s22 3p 3p66 4s 4s22 3d 3d77

They determine the chemical properties of an They determine the chemical properties of an

element. element. For the representative elements, they For the representative elements, they

are the ns are the ns and npand np electrons; electrons; for transitionfor transition

elements they are the elements they are the ns and (nns and (n−1)d−1)d electrons electrons..

1A1A

HH11

LiLi33

NaNa

1111

KK

1919

RbRb

3737

CsCs5555

FrFr8787

11

22

33

44

55

66

77

PP

1s1s11

2s2s11

3s3s11

4s4s11

5s5s11

6s6s11

7s7s11

# of valence electrons = 1

BaBa5656

BeBe44

MgMg

1212

CaCa

2020

SrSr

3838

RaRa8888

2A2A

2s2s22

3s3s22

4s4s22

5s5s22

6s6s22

7s7s22


GaGa3131

InIn4949

TlTl8181

BB55

AlAl1313

3A3A

2s2s22 2p 2p11

3s3s22 3p 3p11

4s4s22 4p 4p11

5s5s22 5p 5p11

6s6s22 6p 6p11


BrBr3535

II5353

AtAt8585

FF99

ClCl1717

7A7A

2s2s22 2p 2p55

3s3s22 3p 3p55

4s4s22 4p 4p55

5s5s22 5p 5p55

6s6s22 6p 6p55

For the representative elements, the # of valence electrons = # of group


The element X has the valence shell The element X has the valence shell electron configuration, nselectron configuration, ns22 np np44. .

X belongs to what group?X belongs to what group?

chalcogenschalcogens

ZnZn

BaBa5656

BeBe44

MgMg

1212

CaCa

2020

SrSr

3838

RaRa8888

2A2A

1A1A

HH11

LiLi33

NaNa

1111

KK

1919

RbRb

3737

CsCs5555

FrFr8787

AcAc UnqUnq UnpUnp UnhUnh UnsUns UnoUno UneUne

HgHgLaLa5757

ScSc

2121

YY

3939

8989

3B3B

TiTi

2222

ZrZr4040

HfHf7272

104104

4B4B

VV

2323

NbNb4141

TaTa7373

105105

5B5B

CrCr2424

MoMo4242

WW7474

106106

6B6B

MnMn

TcTc

ReRe

2525

4343

7575

107107

7B7B

FeFe

OsOs

2626

RuRu4444

7676

108108

8B8B

IrIr

4545

7777

CoCo2727

RhRh

109109

8B8B

NiNi2828

PdPd

4646

PtPt7878

8B8B

CuCu2929

AgAg4747

AuAu7979

1B1B3030

CdCd4848

8080

2B2B

GaGa3131

InIn4949

TlTl8181

BB55

AlAl1313

3A3A

GeGe3232

SnSn5050

PbPb8282

CC66

SiSi1414

4A4A

AsAs3333

SbSb5151

BiBi8383

NN77

PP1515

5A5A

SeSe3434

TeTe5252

PoPo8484

OO88

SS1616

6A6A

BrBr3535

II5353

AtAt8585

FF99

ClCl1717

7A7A

KrKr3636

XeXe5454

RnRn8686

NeNe1010

ArAr1818

HeHe228A8A

Energy (Orbital) DiagramEnergy (Orbital) Diagram

EE

1s1s

2s2s2p2p

3s3s3p3p

4s4s 3d3d

4p4p

Be 1sBe 1s22 2s 2s22

1s1s 2s2s 2p2p 3s3s

BeBe

Orbital Box DiagramsOrbital Box Diagrams

1s1s 2s2s 2p2p

NN

Orbital Box DiagramsOrbital Box Diagrams

Formation of CationsFormation of Cationselectrons lost from subshell with highest electrons lost from subshell with highest

n and n and ll first ( first (from valence electronsfrom valence electrons))

examplesexamples

KK 1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s11

[Ar] [Ar] 4s4s11

KK++ 1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66

[Ar][Ar]

CaCa 1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22

[Ar] [Ar] 4s4s22

CaCa2+2+ 1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66

[Ar][Ar]

Al Al 1s1s22 2s 2s22 2p 2p66 3s3s22 3p 3p11

AlAl3+3+ [Ne] [Ne]

In [Kr] 4dIn [Kr] 4d1010 5s5s22 5p 5p11

InIn3+3+ [Kr] 4d [Kr] 4d1010

Transition Metal CationsTransition Metal CationsIn the process of ionization transition metals In the process of ionization transition metals

the ns electrons are lost before the (n-1)d the ns electrons are lost before the (n-1)d

Fe: [Ar] 3dFe: [Ar] 3d66 4s 4s22 Fe Fe2+2+: [Ar] 3d: [Ar] 3d66

FeFe2+2+: [Ar] 3d: [Ar] 3d66 Fe Fe3+3+: [Ar] 3d: [Ar] 3d55

Cu: [Ar] 3dCu: [Ar] 3d1010 4s 4s11 Cu Cu++: [Ar] 3d: [Ar] 3d1010

CuCu++: [Ar] 3d: [Ar] 3d1010 Cu Cu2+2+: [Ar] 3d: [Ar] 3d99

Fe, FeFe, Fe2+2+, Fe, Fe3+3+, Cu, and Cu, Cu, and Cu2+2+ are paramagnetic are paramagnetic

Two problems of ions, charge, and electron configurationTwo problems of ions, charge, and electron configuration

An anion has a 3An anion has a 3− charge and electron configuration− charge and electron configuration1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66. What is the symbol of the ion. What is the symbol of the ion?? The neutral atom has gained 3e- to form the ion, thenThe neutral atom has gained 3e- to form the ion, thenthe neutral atom had 15 e-. In the neutral atom the # e- the neutral atom had 15 e-. In the neutral atom the # e- = # p+ = Atomic number, that is 15. The element is,= # p+ = Atomic number, that is 15. The element is,then, phosphorus (phosphorus). Symbol of ion is Pthen, phosphorus (phosphorus). Symbol of ion is P33−−..

A cation has a 2+A cation has a 2+ chargecharge and its electron and its electron configuration is [Ar] 3dconfiguration is [Ar] 3d77. What is the symbol of the ion?. What is the symbol of the ion? Here, the neutral atom has lost 2e-. It is a transition Here, the neutral atom has lost 2e-. It is a transition metal, due to the 3d electrons. Remember they firstlymetal, due to the 3d electrons. Remember they firstlylose e-s in 4s orbital. Symbol of ion is Colose e-s in 4s orbital. Symbol of ion is Co2+2+..Neutral atom has 18 + 7 + 2 = 27 e- = 27 p+ = atomic #Neutral atom has 18 + 7 + 2 = 27 e- = 27 p+ = atomic # [Ar] [Ar] 3d3d77 lost lost

Atomic Properties and Periodic Atomic Properties and Periodic TrendsTrends

Periodic Properties of Periodic Properties of

the Elementsthe Elements

1.1. Atomic RadiiAtomic Radii

2.2. Ionization EnergyIonization Energy

3.3. Electron AffinityElectron Affinity

4.4. Ionic RadiiIonic Radii

Atomic Properties and Periodic TrendsAtomic Properties and Periodic Trends

• Establish a classification scheme of the elements Establish a classification scheme of the elements based on their electron configurations.based on their electron configurations.

• Noble GasesNoble Gases– All of them have completely filled electron All of them have completely filled electron

shells. They are not very reactive.shells. They are not very reactive.• Since they have similar electronic structures, Since they have similar electronic structures,

their chemical reactions are similar.their chemical reactions are similar.– HeHe 1s1s22

– NeNe [He] 2s[He] 2s22 2p 2p66

– ArAr [Ne] 3s[Ne] 3s22 3p 3p66

– Kr Kr [Ar] 4s[Ar] 4s22 4p 4p66

– XeXe [Kr] 5s[Kr] 5s22 5p 5p66

– RnRn [Xe] 6s[Xe] 6s22 6p 6p66

Atomic Properties and Periodic TrendsAtomic Properties and Periodic TrendsRepresentative Elements Representative Elements areare

the elements in A groupsthe elements in A groups

on periodic chart.on periodic chart.

These elements will haveThese elements will have

their “last” electron in an their “last” electron in an

outer outer ss or or pp orbital. orbital.

These elements have fairlyThese elements have fairly

regular variations in their regular variations in their

properties.properties.

Metallic character, for expl, Metallic character, for expl,

increases from right to left increases from right to left

and top to bottom. and top to bottom.

Atomic Properties and Periodic TrendsAtomic Properties and Periodic Trends• dd-Transition Elements-Transition Elements

Elements on periodic Elements on periodic

chart in B groups.chart in B groups.

Sometimes called Sometimes called

transition metals.transition metals.• Each metal has Each metal has dd

electrons.electrons.

nnssxx (n-1) (n-1)ddyy configurations configurations• These elements make the These elements make the

transition from metals to transition from metals to nonmetals.nonmetals.

• Exhibit smaller variations Exhibit smaller variations from row-to-row than the from row-to-row than the representative elements.representative elements.

Atomic Properties and Periodic TrendsAtomic Properties and Periodic Trends• ff - transition metals - transition metals

Sometimes called innerSometimes called inner

transition metals.transition metals.

• Electrons are being Electrons are being added to added to ff orbitals. orbitals.

• Electrons are being Electrons are being added two shells below added two shells below the valence shell!the valence shell!

• Consequently, very Consequently, very slight variations of slight variations of properties from one properties from one element to another.element to another.


OutermostOutermost electrons (valence electrons) electrons (valence electrons)

have the greatest Influence on the chemicalhave the greatest Influence on the chemical

properties of elements.properties of elements.


Atomic radiiAtomic radii describe the describe the

relative sizes of atoms.relative sizes of atoms.

Atomic radii increase within aAtomic radii increase within a

column going from the top to column going from the top to

the bottom of the periodic table.the bottom of the periodic table.

The outermost electrons are The outermost electrons are

assigned to orbitals with assigned to orbitals with

increasingly higher values of n. increasingly higher values of n.

The underlying electrons The underlying electrons

require some space, so the require some space, so the

electrons of the outer shells electrons of the outer shells

must be further from the must be further from the

nucleus.nucleus.


Atomic radiiAtomic radii decrease decrease

within a row going fromwithin a row going from

Left to right on theLeft to right on the

periodic table.periodic table.

This last fact seems This last fact seems

contrary to intuition.contrary to intuition.

How does nature make How does nature make

the elements smallerthe elements smaller

even though the electron even though the electron

number is increasing?number is increasing?

Atomic RadiiAtomic Radii• The reason the atomic radii decrease across a The reason the atomic radii decrease across a

period is due to period is due to shieldingshielding or or screeningscreening effect. effect.– Effective nuclear charge, ZEffective nuclear charge, Zeffeff, experienced by , experienced by

an electron is less than the actual nuclear an electron is less than the actual nuclear charge, Z.charge, Z.

– The inner electrons block the nuclear charge’s The inner electrons block the nuclear charge’s effect on the outer electrons.effect on the outer electrons.

• Moving across a period, each element has an Moving across a period, each element has an increased nuclear charge and the electrons are increased nuclear charge and the electrons are going into the same shell (2s and 2p or 3s and 3p, going into the same shell (2s and 2p or 3s and 3p, etc.).etc.).– Consequently, the outer electrons feel a Consequently, the outer electrons feel a

stronger effective nuclear charge.stronger effective nuclear charge.– For Li, ZFor Li, Zeffeff ~ +1 ~ +1– For Be, ZFor Be, Zeffeff ~ +2 ~ +2 — — For B, ZFor B, Zeffeff ~ +3 ~ +3

Atomic RadiiAtomic Radii• Example: Arrange these elements based on Example: Arrange these elements based on

their their increasingincreasing atomic radii. atomic radii.

– Se, S, O, TeSe, S, O, Te

O < S < Se < TeO < S < Se < Te

In the same group atomic size increases In the same group atomic size increases

as n (and Z) increasesas n (and Z) increases

─ ─ Br, Ca, Ge, FBr, Ca, Ge, F

F < Br < Ge < CaF < Br < Ge < Ca

same group same periodsame group same period

Ionization EnergyIonization Energy

• First ionization energy (IEFirst ionization energy (IE11))

– The minimum amount of energy required to The minimum amount of energy required to remove the most loosely bound electron from remove the most loosely bound electron from an isolated gaseous atom to form a 1+ ion.an isolated gaseous atom to form a 1+ ion.

• Symbolically:Symbolically:AtomAtom(g)(g) + energy + energy ion ion++

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

EndothermicEndothermic

Mg(g) + 738kJ/mol Mg+ + e- IE1= IE1= 738kJ/mol

Ionization EnergyIonization Energy• Second ionization energy (IESecond ionization energy (IE22))

– The amount of energy required to remove the The amount of energy required to remove the second electron from a gaseous 1+ ion.second electron from a gaseous 1+ ion.

• Symbolically:Symbolically:– ionion++ + energy + energy ionion2+2+ + e + e--

Mg+ + 1451 kJ/mol Mg2+ + e- IE2= IE2= 1451 kJ/molAtoms can have 3rd (IE3), 4th (IE4), etc. ionization energies. The values are consecutively getting larger.

Ionization EnergyIonization EnergyPeriodic trends for Ionization Periodic trends for Ionization EnergyEnergy::1) IE1) IE22 > IE > IE1 1

It always takes moreIt always takes more energy energy to remove a second electron to remove a second electron from an ion than from a from an ion than from a neutral atom. neutral atom. 2) IE2) IE11 generally increases generally increases moving from IA elements to moving from IA elements to VIIIA elements. VIIIA elements. Important exceptions at Be &Important exceptions at Be &B, N & O, etc. due to B, N & O, etc. due to ss and and ppand half-filled subshells.and half-filled subshells. 3) IE3) IE11 generally decreases generally decreases moving down a family. moving down a family. IEIE1 1 for Li > IEfor Li > IE11 for Na, etc for Na, etc

First Ionization Energies First Ionization Energies of Some Elementsof Some Elements

0

500

1000

1500

2000

2500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Atomic Number

Ionization Energy (kJ/mol)


• Example: Arrange these elements based on Example: Arrange these elements based on their (their (increasingincreasing) first ionization energies.) first ionization energies.

– Sr, Be, Ca, MgSr, Be, Ca, Mg

Sr < Ca < Mg < BeSr < Ca < Mg < Be

– Al, Cl, Na, PAl, Cl, Na, P

Na < Al < P < ClNa < Al < P < Cl

– O, Ga, Sr, SeO, Ga, Sr, Se

Sr < Ga < Se < OSr < Ga < Se < O


• The reason Na forms NaThe reason Na forms Na++ and not Na and not Na2+2+ is is that the energy difference between IEthat the energy difference between IE11 and and

IEIE22 is so large. is so large.

– Requires more than 9 times more energy Requires more than 9 times more energy to remove the second electron than the to remove the second electron than the first one.first one.

• The same trend is persistent throughout The same trend is persistent throughout the series.the series.

– Thus Mg forms MgThus Mg forms Mg2+2+ and not Mg and not Mg3+3+..

– Al forms AlAl forms Al3+3+ and not Aland not Al4+4+..

HH 1312 1312 Ionization Energies (kJ/mole)Ionization Energies (kJ/mole)HeHe 23712371 52475247LiLi 520520 72977297 1181011810BeBe 900900 17571757 1484014840 2100021000BB 800800 24302430 36593659 2502025020 3281032810CC 10861086 23522352 46194619 62216221 3780037800 4730047300NN 14021402 28572857 45774577 74737473 94439443 5325053250 6434064340OO 13141314 33913391 53015301 74687468 1098010980 1332013320 7130071300 8485084850FF 16811681 33753375 60456045 84188418 1102011020 1516015160 1786017860 9200092000NeNe 20802080 39633963 62766276 93769376 1219012190 1523015230NaNa 496496 45654565 69126912 95409540 1336013360 1661016610 2011020110 2549025490MgMg 738738 14501450 77327732 1055010550 1362013620 1800018000 2170021700 2566025660AlAl 577577 18161816 27442744 1158011580 1503015030 1837018370 2329023290 2746027460SiSi 786786 15771577 32293229 43564356 1608016080 1979019790 2378023780 2925029250PP 10121012 18961896 29102910 49544954 62726272 2127021270 2541025410 2984029840SS 10001000 22602260 33803380 45654565 69966996 84908490 2808028080 3172031720ClCl 12551255 22972297 38503850 51465146 65446544 93309330 1102011020 3360033600ArAr 15201520 26652665 39473947 57705770 72407240 88108810 1197011970 1384013840KK 419419 30693069 46004600 58795879 79717971 96199619 1138011380 1495014950

Electron Affinity (EA)Electron Affinity (EA)• Electron affinity is the amount of energy Electron affinity is the amount of energy

absorbed or emittedabsorbed or emitted when an electron is when an electron is added to an isolated gaseous atom to form added to an isolated gaseous atom to form an ion with a 1- charge.an ion with a 1- charge.

• Sign conventions for electron affinity.Sign conventions for electron affinity.

– If EA > 0 energy is absorbed (difficult)If EA > 0 energy is absorbed (difficult)

– If EA < 0 energy is released (easy)If EA < 0 energy is released (easy)

• Electron affinity is a measure of an atom’s Electron affinity is a measure of an atom’s ability to form negative ions.ability to form negative ions.

• Symbolically:Symbolically:

atom(g) + e- ion-(g) EA (kJ/mol)

Electron AffinityElectron Affinity• General periodic trend for electron affinity isGeneral periodic trend for electron affinity is

– the values the values become more negativebecome more negative from left from left to right across a period on the periodic to right across a period on the periodic chart chart ((affinity for electron increases).).

– the values become more negative from the values become more negative from bottom to top at a group on the periodic bottom to top at a group on the periodic chart.chart.

−Noble gases have EA > 0 (full electron confg)

• An element with a high ionization energy generally has a high affinity for an electron, i.e., EA is largely negative. That is the case for halogens (F, Cl, Br, I), O, and S.

Electron AffinityElectron AffinityF (Z= 9) and Cl (Z = 17) have the most negative EAF (Z= 9) and Cl (Z = 17) have the most negative EA

Noble gases, He (2), Ne (10), and Ar (18), EA > 0; also Be, Mg, NNoble gases, He (2), Ne (10), and Ar (18), EA > 0; also Be, Mg, N

They are all first Electron Affinity. They are all first Electron Affinity. A(g)

- + e- A2-(g) EA2(kJ/mol) is the 2nd

Electron AffinityElectron AffinityTwo examples of electron affinity values: Mg(g) + e- + 231 kJ/mol Mg-(g) EA = 231kJ/mol

Br(g) + e- Br-(g) + 323 kJ/mol EA = -323 kJ/mol

Br has a larger affinity for e− than Mg. The greater the affinity an atom has for an e− , the more negative EA is, the smaller it is.

Ionic RadiiIonic RadiiCations (positive ions) are always smaller than

their respective neutral atoms. When one or more electrons are removed, the attractive force of the protons is now exerted on less electrons.

ElementElement NaNa

11 p+, 11e11 p+, 11e-

MgMg

12p+, 12 e12p+, 12 e--

AlAl

13 p+, 13e13 p+, 13e-

Atomic Atomic Radius (Radius (Å)Å)

1.861.86 1.601.60 1.431.43

IonIon NaNa++

11 p+, 10e11 p+, 10e-

MgMg2+2+

12 p+, 10 e12 p+, 10 e--

AlAl3+3+

13 p+, 10e13 p+, 10e-

Ionic Ionic

Radius (Radius (Å)Å)

1.161.16 0.850.85 0.680.68

Ionic RadiiIonic RadiiAnions (negative ions) are always larger than

their neutral atoms.

F 1s2 2s2 2p5 + e− F− 1s2 2s2 2p6 same Z nine electrons ten electrons

ElementElement NN

7 p+, 7e7 p+, 7e-

OO FF

AtomicAtomic

Radius(Radius(Å)Å)

0.750.75 0.730.73 0.720.72

IonIon NN3-3-

7 p+, 7 p+, 10e10e-

OO2-2-

8 p+, 8 p+, 10e10e-

FF−−

9 p+, 9 p+, 10e10e-

IonicIonic

Radius(Radius(Å)Å)

1.711.71

The threeThe three

1.261.26

ions are ions are

1.191.19isoelectronicisoelectronic

Ionic RadiiIonic Radii

Cation (positive ions) radii decrease from left to right across a period.

Increasing nuclear charge attracts the electrons and decreases the radius.Rb+ and Sr2+ are isoelectronic, same # of e-s

IonIon RbRb++

Z = 37 pZ = 37 p++

SrSr2+2+

Z = 38 pZ = 38 p++

InIn3+3+

Z = 49 pZ = 49 p++

IonicIonic

Radii(Radii(Å)Å) 1.661.66 1.321.32 0.940.94

Ionic RadiiIonic Radii

Anion (negative ions) radii decrease from left to right across a period.

Increasing electron numbers in highly charged ions cause the electrons to repel and increase the ionic radius.For these isoelectronic anions… 10 e− and 7 p+ 8 p+ 9 p+

IonIon NN3-3- OO2-2- FF−−

IonicIonic

Radii(Radii(Å)Å)

1.711.71 1.261.26 1.191.19

Ionic RadiiIonic RadiiExample: Arrange these ions in order of decreasing radius.

Ga3+, K+, Ca2+

K+ > Ca2+ > Ga3+

Cl−, Se2−, Br−, S2−

Se2− > Br− > S2− > Cl−

isoelectronic isoelectronic, same # of electrons

Se2−(34 p+) > Br−(35 p+); they have 36 e− each.

S2−(16 p+) > Cl−(17 p+); they have 18 e− each.

Br− > S2− because Br− is in the 4th period, S2− is in the 3rd.

Ionic Radii of isoelectronic speciesIonic Radii of isoelectronic speciesIsoelectronic species have the same number of electrons. Here are some examples with the number of (protons) and + or − charges

N3−(Z=7) > O2−(Z=8) > F−(Z=9) > Ne(Z=10) neutral >

Na+(Z=11) > Mg2+(Z=12) > Al3+ (Z=13) all have 10e−

The nuclear charge (+) increases from left to right, so does attraction force to electrons: r decreases.

S2−(Z=16) > Cl− (Z=17) > Ar0 (Z=18) > K+ (Z=19) >

Ca2+ (Z=20) > Sc3+ (Z=21) all of them have 18e−

Chapter 8 Atomic Electron Configurations and Chemical Periodicity.

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Transcript of Chapter 8 Atomic Electron Configurations and Chemical Periodicity.