Question

what is electron affinity?

Answer 1

This is the amount of energy that is released when an electron is added to an atom to form a negative charge. The electron affinity depends on the size of the atom as well as the number of protons in the nucleus. Electron affinity decreases down a group and increases across a period.

Answer 2

electron affinity can also be thought of as the "desire" of an atom to gain an extra electron. Atoms like fluorine really "want" an extra electron, since that will fill their valence shell, so fluorine has a high EA. Atoms like sodium have no desire to gain an electron, so it will have a low EA.