Electron affinity

In chemistry, electron affinity is the amount of energy absorbed when an electron is added to a neutral isolated gaseous atom to form a gaseous ion with a 1- charge. It has a negative value if energy is released.

Most elements have a negative electron affinity. This means they do not require energy to gain an electron; instead, they release energy. Atoms more attracted to extra electrons have a more negative electron affinity. Chlorine most strongly attracts extra electrons; radon most weakly attracts an extra electron.

Although electron affinities vary in an chaotic manner across the table, some patterns amerge. Generally, nonmetals have more negative electron affinities than metals. However, the noble gases are an exception: they have positive electron affinities.

Electron affinity is influenced by the octet rule. Group 1 elements (hydrogen h, lithium, sodium, potassium, rubidium, calcium, and francium) tend to gain an electron and form -1 anions. The noble gases have a full octet, and thus adding an extra electron requires large amounts of energy, but it is possible.

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Period
1 H
-73
He
21
2 Li
-60
Be
19
B
-27
C
-122
N
7
O
-141
F
-328
Ne
29
3 Na
-53
Mg
19
Al
-43
Si
-134
P
-72
S
-200
Cl
-239
Ar
35
4 K
-48
Ca
10
Sc
-18
Ti
-8
V
-51
Cr
-64
Mn
 
Fe
-16
Co
-64
Ni
-112
Cu
-118
Zn
47
Ga
-29
Ge
-116
As
-78
Se
-195
Br
-325
Kr
39
5 Rb
-47
Sr
 
Y
-30
Zr
-41
Nb
-86
Mo
-72
Tc
-53
Ru
-101
Rh
-110
Pd
-54
Ag
-126
Cd
32
In
-29
Sn
-116
Sb
-103
Te
-190
I
-295
Xe
41
6 Cs
-45
Ba
 
Lu
 
Hf
 
Ta
-31
W
-79
Re
-14
Os
-106
Ir
-151
Pt
-205
Au
-223
Hg
61
Tl
-20
Pb
-35
Bi
-91
Po
-183
At
-270
Rn
41
7 Fr
-44
Ra
 
Lr
 
Rf
 
Db
 
Sg
 
Bh
 
Hs
 
Mt
 
Ds
 
Uuu
 
Uub
 
Uut
 
Uuq
 
Uup
 
Uuh
 
Uus
 
Uuo
 
Periodic table of electron affinities, in kJ/mol



copyright 2004 FactsAbout.com