Atomic Electron Configurations and Chemical Periodicity

We know the electronic structure of the hydrogen atomstates as determined by the quantum numbers n, l and m.

How does this apply to larger atoms? i.e. multiple electron systems

How does the electron structure relate to the periodic table ?

How does the electron structure relate to the chemical properties of atoms ?

Electron Spin and Magnetism

Before we can talk about structure we need to learn a bit about the magnetic properties of particles.

Recall that electron move the nucleus in orbits corresponding to set angular momentum values

Recall, also that when electrons move they generate a magnetic field, B.

v

BThis is analogous to electrical current moving through a loop

Electrons in orbit generate magnetic fields, therefore all materials are magnetic. Is that so?

Imagine two electrons in the same orbit moving in opposite directions.

B

v v

B

Electron Spin and Magnetism

The magnetic fields cancel !!

Do electrons occur in pairs in orbitals!!!

But not for this reason, since this is not physically correct.

Motion of electrons in their orbitals is not responsible for magnetism, even when the electron is unpaired.

The net magnetic field averages to zero.

Yes!

Electron Spin and MagnetismWhen a beam of atomic hydrogen is passed through a non-uniform magnetic field is splits into two beams

This Magnetism is not due to due to orbital motion

Another source of magnetism

From where?

Spin

Electron Spin and Magnetism

When an external magnetic field is applied the electron will either align along or against the field.

Being aligned with the field is more stable than against, therefore the up orientation is slightly favored

Electron spin is an inherent magnetism associated with it, which has nothing to do with its translational motion.

The electron can the thought of as a little magnet

More stable Less stable

The distribution of up to down depends on strength of the applied magnetic field.

B

UP (s=1/2) DOWN (s=-1/2)

Magnetic field

Magnetic Materials

Paramagnetic Materials

Diamagnetic Materials

More electron electrons will align with the field than against the externally applied field.

Composed of atoms/molecules containing only paired electrons

They are repelled by an externally applied magnetic field.

Composed of atoms/molecules with unpaired electrons.

The result is a net bulk magnetic field parallel to the applied field, hence an attractive force

Ferromagnetic Materials – Have a permanent magnetic field

The magnetic field from each atom will add up, as long as the atoms are correctly aligned to give a one strong “bulk’ magnetic field. – ie. Magnets

When two electron on separate atoms are close, the field from one will cause the other to align with it as it would be more stable

Magnetic Materials

Pauli Exclusion PrincipleFermions - particles have spin ½.

electrons protons neutrons

“Fermions cannot occupy the same space and spin coordinates”

This means that no two electrons can have the same quantum numbers, including the spin quantum numbers.

Therefore each orbital can only have 2 electrons since there are only two spin states s =1/2 and -1/2.

Example: 1s orbital n = 1, l = 0, m = 0 and s = 1/2 or s = -1/2

1s Orbital

Atoms with more than one electronMulti-electron wavefunctions are similar to those for the H atom

The ground state of such atoms requires that the lowest possible energy wavefunctions be “occupied”

box diagram - a simple tool used to add or subtract electrons from the boxes to represent the electron configuration of the element

Consider H, He, Li and Be

B 5

C 6

N 7

O 8

F 9

Ne 10

1s 2p2sHunds rule

Element # e’s

Electrons added to each empty orbital in parallel

When no new orbitals are available they are paired

Maximize spin

Electron Configuration

2 2Be 1 2s s1 18

1s1 1

2

13

14

15

16

17

1s2

2

2s1 3

2s2

4

2p1

5

2p2

6

2p3

7

2p4

8

2p5

9

2p6

10

3s1 11

3s2

12

3

4

5

6

7

8

9

10

11

12

3p1

13

3p2

14

3p3

15

3p4

16

3p5

17

3p6

18

4s1 19

4s2

20

3d1

21

3d2

22

3d3

23

4s13d5 24

3d5

25

3d6

26

3d7

27

3d8

28

4s13d10 29

3d10

30

4p1

31

4p2

32

4p3

33

4p4

34

4p5

35

4p6

36

5s1 37

5s2

38

4d1

39

4d2

40

5s14d4 41

5s14d5 42

4d5

43

5s14d7 44

5s14d8 45

5s04d10 46

5s14d10 47

4d10

48

5p1

49

5p2

50

5p3

51

5p4

52

5p5

53

5p6

54

6s1 55

6s2

56

La-Lu

5d2

72

5d3

73

5d4

74

5d5

75

5d6

76

5d7

77

6s15d9 78

6s25d10 79

5d10

80

6p1

81

6p2

82

6p3

83

6p4

84

6p5

85

6p6

86

7s1 87

7s2

88

Ac-Lr

6d2

104

6d3

105

6d4

106

6d5

107

6d6

108

6d7

109

110

111

4f05d1 57

4f15d1

58

4f3

59

4f4

60

4f5

61

4f6

62

4f7

63

4f75d1 64

4f9

65

4f10

66

4f11

67

4f12

68

4f13

69

4f14

70

5d1

71

5f06d1

89

5f06d2

90

5f26d1

91

5f36d1

92

5f46d1

93

5f6

94

5f7

95

5f76d1 96

5f9

97

5f10

98

5f11

99

5f12

100

5f13

101

5f14

102

6d1

103

A shorthand notation is commonly used to write out the electron configuration of the atoms based on the number of electrons within each subshell

It consists of: NUMBER LETTER SUPERSCRIPT(shell i.d.) (subshell) (occupancy)

B 5

C 6

N 7

O 8

F 9

Ne 10

1s 2p2s

Electron ConfigurationElement # e’s

1s2 2s2 2p1

1s2 2s2 2p2

1s2 2s2 2p3

1s2 2s2 2p4

1s2 2s2 2p5

1s2 2s2 2p6

Aufbau order and Energy LevelsThe sequence of subshells in the electron configurations not the same as the energy levels of H

The experimental sequence is known as the aufbau order

It is a consequence of electron-electron interactions have on the energies of the wavefunctions in all multi-electron atoms

Levels within subshells are still degenerate, the subshells in each shell are no longer degenerate in each shell, and differ in energy as s < p < d,

Some subshells can overlap the levels of a different shell; thus, for example, in neutral atoms 4s lies below 3d

Traditional aufbau sequence diagramInstead of filling orbitals in order of increasing n, we should really be filling them in order of increasing n + l

n is used as a ‘tiebreaker’ i.e the one with lowest n first

Ex) Fluorine 9 e’s

1s2 2s2 2p5

Ex) Scandium 21 e’s

1s2 2s2 2p63s2 3p64s23d1

Ex) Strontium 38 e’s

1s2 2s2 2p63s2 3p64s23d10

4p6 5s2

Afbau sequence from Periodic Table

1.008 H 1

2

13

14

15

16

17

4.003 He

2 6.939

Li 3

9.012 Be

4

10.811 B

5

12.011 C

6

14.007 N

7

15.999 O

8

18.998 F

9

20.183 Ne

10 22.990

Na 11

24.312 Mg

12

3

4

5

6

7

8

9

10

11

12

26.982 Al

13

28.086 Si

14

30.974 P

15

32.064 S

16

35.453 Cl

17

39.948 Ar

18 39.102

K 19

40.08 Ca

20

44.956 Sc

21

47.90 Ti

22

50.942 V

23

51.996 Cr

24

54.938 Mn

25

55.847 Fe

26

58.933 Co

27

58.71 Ni

28

63.546 Cu

29

65.37 Zn

30

69.72 Ga

31

72.59 Ge

32

74.922 As

33

78.96 Se

34

79.904 Br

35

83.80 Kr

36 85.47

Rb 37

87.62 Sr

38

88.905 Y

39

91.22 Zr

40

92.906 Nb

41

95.94 Mo

42

(98) Tc

43

101.07 Ru

44

102.90 Rh

45

106.4 Pd

46

107.87 Ag

47

112.40 Cd

48

114.82 In

49

118.69 Sn

50

121.75 Sb

51

127.60 Te

52

126.90 I

53

131.30 Xe

54 132.91

Cs 55

137.33 Ba

56

138.91 La

57

178.49 Hf

72

180.95 Ta

73

183.85 W

74

186.21 Re

75

190.22 Os

76

192.2 Ir

77

195.09 Pt

78

196.97 Au

79

200.59 Hg

80

204.38 Tl

81

207.19 Pb

82

208.98 Bi

83

(209) Po

84

(210) At

85

(222) Rn

86 (223)

Fr 87

226.025 Ra

88

227.029 Ac

89

(261) Rf

104

(262) Ha

105

(263) Sg

106

(262) Ns

107

(265) Hs

108

(266) Mt

109

new

110

new

111

140.12 Ce

58

140.91 Pr

59

144.24 Nd

60

(145) Pm

61

150.36 Sm

62

151.97 Eu

63

157.25 Gd

64

158.93 Tb

65

162.50 Dy

66

164.93 Ho

67

167.26 Er

68

168.93 Tm

69

173.04 Yb

70

174.97 Lu

71

232.04 Th

90

231.04 Pa

91

238.03 U

92

237.05 Np

93

(244) Pu

94

(243) Am

95

(247) Cm

96

(247) Bk

97

(251) Cf

98

(252) Es

99

(257) Fm

100

(258) Md

101

(259) No

102

(260) Lr

103

s block

d block

p block

f block

We can appreaciate that the origin of the periodic table is the electron configurations of the elements

The periodic table can be used to determine the afbau order instead

As you increase the # electrons, the block structure indicates the sequence of subshells

A more detailed look at the block structure

21

2

43 3

3 45 4 56

4

5 67

5

6

The core electrons are represented by the noble gas followed by configuration of the valence electrons.

Electron configurations for the larger elements are lengthy to write out.

Ex) Ne has an electron configuration of 1s22s22p6.

For Na, we can write either 1s22s22p63s1 or [Ne]3s1

Electron Configurations

Ex) Sr 38 1s2 2s2 2p63s2 3p64s23d10 4p6 5s2

1s2 2s2 2p63s2 3p64s23d104p6Kr 36

[Kr] 5s2

Core e’s

Valence e’s

noble gas notation - the symbol for a noble gas is used as an abbreviation for its electrons.

How many core and valence electrons do these atoms have?

a) ____core, ____valence c) ____core, ____valenceb) ____core, ____valence d) ____core, ____valence

Identify the elements with the following electron configurations.

a) 1s22s22p3 c) [Ne]3s23p3

b) 1s22s22p63s23p64s23d7 d) [Kr]5s24d5

Exercises

NCo

PTc

2 5 10 518 9 36 7

Exceptions to the aufbau order

1 18

1s1 1

2

13

14

15

16

17

1s2

2

2s1 3

2s2

4

2p1

5

2p2

6

2p3

7

2p4

8

2p5

9

2p6

10

3s1 11

3s2

12

3

4

5

6

7

8

9

10

11

12

3p1

13

3p2

14

3p3

15

3p4

16

3p5

17

3p6

18

4s1 19

4s2

20

3d1

21

3d2

22

3d3

23

4s13d5 24

3d5

25

3d6

26

3d7

27

3d8

28

4s13d10 29

3d10

30

4p1

31

4p2

32

4p3

33

4p4

34

4p5

35

4p6

36

5s1 37

5s2

38

4d1

39

4d2

40

5s14d4 41

5s14d5 42

4d5

43

5s14d7 44

5s14d8 45

5s04d10 46

5s14d10 47

4d10

48

5p1

49

5p2

50

5p3

51

5p4

52

5p5

53

5p6

54

6s1 55

6s2

56

La-Lu

5d2

72

5d3

73

5d4

74

5d5

75

5d6

76

5d7

77

6s15d9 78

6s15d10 79

5d10

80

6p1

81

6p2

82

6p3

83

6p4

84

6p5

85

6p6

86

7s1 87

7s2

88

Ac-Lr

6d2

104

6d3

105

6d4

106

6d5

107

6d6

108

6d7

109

110

111

Developed by Prof. R. T. Boeré (updated January, 1999)

4f05d1 57

4f15d1

58

4f3

59

4f4

60

4f5

61

4f6

62

4f7

63

4f75d1 64

4f9

65

4f10

66

4f11

67

4f12

68

4f13

69

4f14

70

5d1

71

5f06d1

89

5f06d2

90

5f26d1

91

5f36d1

92

5f46d1

93

5f6

94

5f7

95

5f76d1 96

5f9

97

5f10

98

5f11

99

5f12

100

5f13

101

5f14

102

6d1

103

Exceptions to Afbau order result of: Full shell stabilityHalf Shell stability

Stability of higher spin state

Cr Cu

Valence RevisitedElectron configurations for fourth row from Gallium and beyond.

Ex) Ar At. No. = 18 1s22s22p63s23p6.

Then for Ga we should write: [Ar] 4s23d104p1

Ex) Ga At. No. = 31 1s2 2s2 2p63s2 3p64s23d10 4p1

It has 3d10 electron that belong to the 3 shell not the 4 shell, hence it is strictly speaking not part of the valence if it is complete and should be considered as part of the core.

What is the valence for Ga?

Therefore: [Ar]3d10 is the core and 4s24p1 is the valence

How about Thallium 81?

Electron configurations of ionsElectron configurations of ions can be determined from that of the neutral atom, i.e. electron configurations predict ions

Oxide forming from oxygen:

Same electron configuration as neon

This rationalizes the kinds of stable ions that are formed for certain elements

O = 1s22s22p4 O2- = 1s22s22p6 Ne = 1s22s22p6

Mg = 1s22s22p63s2 Mg2+ = 1s22s22p6

Magnesium cation from magnesium:Ne = 1s22s22p6

Same electron configuration as neon

Electron configurations of ionsThus, cation electron configuration is obtained by removing electrons in the reverse Aufbau sequence

Anion electron configurations are obtained by adding electrons in the usual Aufbau sequence

Ions try to achieve:

(1) the closest noble gas configuration

(2) a pseudo noble gas configuration (closed d or f subshell)(3) a noble gas configuration for everything except d or f electrons

Cations always have their electron configurations in the sequence of the H.

1. Li+ 21 [ ]s He

Nearest stable CoreValence

2s1 = 1 e-

2. Br- [Ar]4s23d104p5 4s24p5 = 7 e- [Ar]4s23d104p6=[Kr]

21 [ ]s He

Core

[Ar]3d10

E.C of Element

1s22s1

Electron configurations of ions

1. C4+

2. P3-

3. Ga3+

21 [ ]s He

2 2 6 2 61 2 2 3 3 [ ]s s p s p Ar

2 2 6 2 3 101 2 2 3 3 3s s p s p d

4. Sn2+

5. Sn4+

2 10[ ]5 4Kr s d

10[ ]4Kr d

Nearest stable Core

1s22s22p2

Valence

2s22p2

3p3

4s24p1

E.C of Element

5p2

5s25p2

[Ne]3s23p3

[Ar]3d104s24p1

[Kr]5s24d105p2

[Kr]5s24d105p2

a) O2- c) Cl+ e) Pb4+

b) Mg6- d) Ca+ f) Ga3+

Which of the following ions are likely to form? For those which are not what ion would you expect to form from that element?

Exercise

O2- =1s22s22p6 O = 1s22s22p4 = Ne

Mg = 1s22s22p6 3s2

8

12 Mg6- = 1s22s22p6 3s2 3p6 = Ar

Cl = 1s22s22p6 3s23p5 17 Cl1+ = 1s22s22p6 3s23p4

20 Ca = 1s22s22p6 3s23p6 4s2 Ca1+ = 1s22s22p6 3s23p6 4s1

Pb = [Xe]6s24f145d106p2 Pb4+ = [Xe]4f145d1082

Ga = [Ar]4s23d104p131 Ga3+ = [Ar]3d10

a)b)

c)

d)

e)

f )

10

18

16

19

78

28

Order of Energy Levels in Ions“Aufbau” energy levels: s below d

“Aufbau” energy levelsIn Cations

Energy levels in Anions

Electrons more strongly bound as e-n interaction are increased

Electrons less strongly bound as e-n interaction are decreased