High Quality Content by WIKIPEDIA articles! Ion-association is a chemical reaction whereby ions of opposite electrical charge come together in solution to form a distinct chemical entity. Ion-associates are classified according to the number of ions that associate with each other, and the nature of the interaction. The most important factor to determine the extent of ion-association is the dielectric constant of the solvent. Ion-associates have been characterized by means of vibrational spectroscopy. The concept has been proposed by Niels Bjerrum.