Stock nomenclature

Stock nomenclature, sometimes call the Stock system, is a system of chemical nomenclature used for some inorganic compounds, particularly ionic compounds of the transition metals. It was first proposed by German chemist Alfred Stock in 1919, and is one of the systems of inorganic nomenclature recommended for use by the International Union of Pure and Applied Chemistry (IUPAC).

The principle of Stock nomenclature is the the indication of the oxidation state of one or more of the elements in the compound. This is important for elements which have more than one common oxidation states, e.g. the majority of the transition metals. Copper, for example, forms two chlorides, CuCl and CuCl₂: these are named copper(I) chloride and copper(II) chloride respectively. The oxidation number is placed in parentheses immediately after the name of the element it refers to (there is no space between the end of the element name and the opening parenthesis): roman numerals are used for oxidation numbers, which are assumed to be positive unless a minus sign is present, e.g. sodium pentacarbonylmanganate(−I).

Cations

For simple monoatomic cations in ionic compounds, the oxidation number is the same as the charge number of the ion. Some elements form polyatomic cations, for which the oxidation state must be calculated by the normal rules, for example oxidovanadium(IV), VO²⁺; dioxidouranium(VI), UO2+2.

Anions

It is not usually necessary to give the oxidation state for simple monoatomic anions: hence, chloride is assumed to refer to the species Cl⁻, and it is unnecessary to write chloride(−I).