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