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