Electron Affinities of the Main-Group Elements*

The electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion. For example, when a neutral chlorine atom in the gaseous form picks up an electron to form a Cl- ion, it releases an energy of 349 kJ/mol or 3.6 eV/atom. It is said to have an electron affinity of -349 kJ/mol and this large number indicates that it forms a stable negative ion. Small numbers indicate that a less stable negative ion is formed. Groups VIA and VIIA in the periodic table have the largest electron affinities.

* Alkali earth elements (Group IIA) and noble gases (Group VIIIA) do not form stable negative ions.

Electron Affinities in kJ/mole
Period
IA
IIIA
IVA
VA
VIA
VIIA
Period 1
H
...
...
...
...
...
-73
...
...
...
...
...
Period 2
Li
B
C
N
O
F
-60
-27
-122
0
-141
-328
Period 3
Na
Al
Si
P
S
Cl
-53
-44
-134
-72
-200
-349
Period 4
K
Ga
Ge
As
Se
Br
-48
-30
-120
-77
-195
-325
Period 5
Rb
In
Sn
Sb
Te
I
-47
-30
-121
-101
-190
-295
Period 6
Cs
Tl
Pb
Bi
Po
At
-45
-30
-110
-110
-180
-270

Electron Affinities in Electron Volts
1 kJ/mol = .010364 eV/atom
Period
IA
IIIA
IVA
VA
VIA
VIIA
Period 1
H
...
...
...
...
...
-0.76
...
...
...
...
...
Period 2
Li
B
C
N
O
F
-0.62
-0.28
-1.27
0
-1.43
-3.41
Period 3
Na
Al
Si
P
S
Cl
-0.55
-0.46
-1.39
-0.75
-2.08
-3.62
Period 4
K
Ga
Ge
As
Se
Br
-0.50
-0.31
-1.25
-0.80
-2.02
-3.37
Period 5
Rb
In
Sn
Sb
Te
I
-0.49
-0.31
-1.26
-1.05
-1.97
-3.06
Period 6
Cs
Tl
Pb
Bi
Po
At
-0.47
-0.31
-1.14
-1.14
-1.87
-2.80
Periodic Table Chemical bonds
Index

Tables

Reference
Ebbing
Sec 8.5
 
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