Editing Electron affinity (section)

{{Short description|Energy release on formation of anions}}
The '''electron affinity''' (''E''<sub>ea</sub>) of an [[atom]] or [[molecule]] is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.
::X(g) + e<sup>−</sup> →  X<sup>−</sup>(g) + energy
This differs by sign from the energy change of [[electron capture ionization]].<ref name="Compendiumof"/> The electron affinity is positive when energy is released on electron capture.

In [[solid state physics]], the electron affinity for a surface is defined somewhat differently ([[Electron affinity#"Electron affinity" as defined in solid state physics|see below]]).