Electron affinity
From Exampleproblems
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 emerge. 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 17 elements (fluorine, chlorine, bromine, iodine, and astatine) 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 -349 |
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 |
Rg |
Uub |
Uut |
Uuq |
Uup |
Uuh |
Uus |
Uuo |
|
See also
es:Afinidad electrónica he:זיקה אלקטרונית ja:電子親和力 pt:Afinidade eletrônica
The electron affinities in groups 2 and 12 of the periodic table are shown as positive, but should be shown as negative values. Source: C. E. Moore, National Standard Reference Data Series 34, National Bureau of Standards, U.S. Government Printing Office, Washington, DC, 1970.
