SOLVATION

"Ions in solution are always surrounded by solvent molecules. A few of these molecules will be more or less strongly attached to the ion (mainly because of the attraction of the charged ion and the dipole of the solvent molecule) and this assembly may be considered as a single unit for some purposes. E.g., the solvent molecules will move together with the ion during diffusion and electromigration. The number of solvent molecules so attached to an ion is called the ""solvation number."" The surface of an electrode also can, and usually is, solvated. Since the electrodes usually have some excess charge (see electrical double layer,) they also attract the solvent dipoles, and the electrode surface is usually covered by a monolayer of strongly oriented solvent molecules. Under certain extreme conditions, a solution can contain free electrons that are stabilized by solvation. "