The keenness with which an ion exchanger takes up and holds on to a counter-ion. Affinities are very much affected by the concentration of the electrolyte surrounding the ion exchanger. They are usually relegated to elements in groups 17 and 16 in the periodic table. Electron affinities have the capability of being positive with the addition of energy to the system, negative when energy is released with the addition of an election, or zero when there is neutrality in the process.