What is "electron affinity"

n. (context physics English) The energy released when an electron is attached to an atom or molecule; used as a measure of its ability to form an anion

In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

In solid state physics, the electron affinity for a surface is defined somewhat differently (see below).

This page deals with the electron affinity as a property of isolated atoms or molecules (i.e. in the gas phase). Solid state electron affinities are not listed here.