n. | 1. | (Elec. Chem.) an atom or goup of atoms (radical) carrying an electrical charge. It is contrasted with neutral atoms or molecules, and free radicals. Certain compounds, such as sodium chloride, are composed of complementary ions in the solid (crystalline) as well as in solution. Others, notably acids such as hydrogen chloride, may occur as neutral molecules in the pure liquid or gas forms, and ionize almost completely in dilute aqueous solutions. In solutions (as in water) ions are frequently bound non-covalently with the molecules of solvent, and in that case are said to be solvated. According to the electrolytic dissociation theory, the molecules of electrolytes are divided into ions by water and other solvents. An ion consists of one or more atoms and carries one unit charges of electricity, 3.4 x 10-10 electrostatic units, or a multiple of this. Those which are positively electrified (hydrogen and the metals) are called cations; negative ions (hydroxyl and acidic atoms or groups) are called anions. |