Chemistry

Electron affinity

Electron affinity (E_EA) is opposite to ionisation energy (E_i) and is the energy released when an atom gains one electron. For example, the electron affinity for F is –322 kJ mol^–1 and relates to the process:

F(g) + e^– → F^– (g).

Electron affinity increases across a period. For example, E_EA of P is –72 kJ mol^–1, S is –200 kJ mol^–1, Cl is –349 kJ mol^–1, respectively.

Ionisation energies and electron affinities are both a measure of the tendency of atoms to form ions and hence are integral to understanding the characteristics and chemical properties of ionic compounds. The periodicity of E_i and E_EA are particularly important in differentiating between ionic and covalent compounds and for rationalising chemical and physical properties.