What is electron affinity?

Simply, it is the amount of energy released when an electron is added in the outermost shell of an isolated gaseous atom. Affinity means attraction. Hence, electron affinity means tendency of an atom to accept an electron to form an anion. In periodic table, it increases from left to right in a period whereas it decreases from top to bottom in the group.

Electron affinity is the electron gained and it exists on Group 6 and 7 of the periodic table. Group seven is the first electron affinity wherein one mole of atom releases energy after obtaining an electron to produce an electron. Group six is the second electron affinity wherein one mole of atom requires energy after obtaining an electron to produce twp electrons.