Oxidation number
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In chemical nomenclature, the oxidation number (formerly known as the Stock number) of an element in a molecule or complex is the charge that it would bear if all the ligands were removed along with the electron pairs that were shared with the central atom. It is used in the Stock nomenclature of inorganic compounds. It is represented by a Roman numeral: the plus sign is omitted for positive oxidation numbers. The oxidation number is placed either as a right superscript to the element symbol, e.g. FeIII, or in parentheses after the name of the element, e.g. iron(III): in the latter case, there is no space between the element name and the oxidation number.
The oxidation number is usually numerically equal to the oxidation state of the central atom. However the oxidation state of transition metals in certain of their complexes can be difficult to ascertain, hence the slightly different formalism for defining an unambiguous oxidation number for the purposes of nomenclature. The approximation is that the electron pairs forming the coordination bonds are mostly associated with the ligands: this is a good approximation for most Werner-type complexes, but much less true for organometallic compounds as well as for certain hydrido complexes, dithiolene complexes and nitrosyl complexes.
External links
- ["Oxidation number"] from the IUPAC Gold Book (PDF file)
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