(1) A cation (with its counterion) derived by addition of a hydron to a mononuclear parent hydride of the nitrogen, chalcogen and halogen family, e.g. H4N+ ammonium ion.
(2) Derivatives formed by substitution of the above parent ions by univalent groups, e.g. (CH3)2S+H dimethylsulfonium, (CH3CH2)4N+ tetraethylammonium.
(3) Derivatives formed by substitution of the above parent ions by groups having two or three free valencies on the same atom. Such derivatives are, whenever possible, designated by a specific class name. E.g. R2C=NH2+ iminium ion. IUPAC CLASS NAMES (1993). See also carbenium ion, carbonium ion.
