Oxide - Nomenclature and Formulas

Nomenclature and Formulas

Oxides are sometimes named according the metal-oxygen ratio. Thus, NbO would be called niobium monoxide and TiO₂ is titanium dioxide. This naming follows the Greek numerical prefixes. In the older literature and continuing in industry, oxides are named by contracting the element name with "a." Hence alumina, magnesia, chromia, are, respectively, Al₂O₃, MgO, Cr₂O₃.

Special types of oxides are peroxide, O₂2−, and superoxide, O₂−. In such species, oxygen is assigned higher oxidation states than oxide.

The chemical formulas of the oxides of the chemical elements in their highest oxidation state are predictable and are derived from the number of valence electrons for that element. Even the chemical formula of O₄, tetraoxygen, is predictable as a group 16 element. One exception is copper, for which the highest oxidation state oxide is copper(II) oxide and not copper(I) oxide. Another exception is fluoride, which does not exist as one might expect—as F₂O₇—but as OF₂.

Since fluorine is more electronegative than oxygen, oxygen difluoride (OF₂) does not represent an oxide of fluorine, but instead represents a fluoride of oxygen.