09) Introduction 9
09) Introduction 9
09) Introduction 9
Zeff = Z - S
where Z = nuclear charge,
Zeff = effective nuclear charge,
S = screening (or shielding) constant
For K, Z =19
The effective nuclear charge experienced by the 4s
electron for the configuration 1s2 2s2 2p6 3s2 3p6 4s1 is:
Zeff = Z - S
= 19 - [(8 x 0.85) + (10 x 1.00)]
= 2.20
For the configuration 1s2 2s2 2p6 3s2 3p6 3d1 is:
Zeff = Z - S
= 19 - (18 x 1.00)
= 1.00
Thus, in the ground state of potassium, it is the 4s atomic orbital
(which feels greater Zeff, more stable) that is occupied.
Electronic Configurations
Lanthanides and Actinides
of
Transition
Metals,
including
Exercises:
1. Use Slaters rules to estimate values of Zeff for (a) a 4s and (b)
a 3d electron in a V atom.
2. Based on Zeff values, which is the possible valence
configuration of the ground state of a V+ ion, 3d3 4s1 or 3d2
4s2.
3. Based on the schematic E level below, what is the electronic
configuration of Fe+ and V+.
Ionization energies, IE
The first ionization energy, IE1, of an atom is the internal energy
change at 0 K, !U(0 K), associated with the removal of the first
valence electron in the gas phase.
X(g) " X+(g) + e
ma
jor c
h
ang
r ch
ang
"e = $
N(N #1)
K
2
!
Electron affinities
The first electron affinity (EA1) is minus the internal energy
change (EA = -!U) for the gain of an electron by a gaseous
atom.
Y(g) + e " Y-(g)
The second electron affinity of atom Y is defined for process
Y-(g) + e " Y-2(g)
Element
Radius (pm)
3
11
19
37
55
Li+
Na+
K+
Rb+
Cs+
90
116
152
166
181
4
12
20
38
56
Be2+
Mg2+
Ca2+
Sr2+
Ba2+
59
86
114
132
149
Other cations
13
30
Al3+
Zn2+
68
88
Halide ions
9
17
35
53
FClBrI-
119
167
182
206
Other anions
8
16
O2S2-
126
170
Anions are generally larger than cations with similar numbers of electrons (Fand Na+ differ only in nuclear charge, but the radius of fluoride is 37% larger)
Protons
Electrons
Radius (pm)
O2-
10
126
F-
10
119
Na+
11
10
116
Mg2+
12
10
86
Protons
Electrons
Radius (pm)
O2-
10
126
S2-
16
18
170
Se2-
34
36
184
Te2-
52
54
207
Protons
Electrons
Radius (pm)
Ti2+
22
20
100
Ti3+
22
19
81
Ti4+
22
18
75