trivalent

Trivalent is an adjective used in chemistry and related fields to indicate valence of three or an oxidation state of +3. It is applied to elements, ions, and compounds that can form three covalent bonds or carry a +3 charge. The term derives from tri- meaning three and valence, the combining capacity of an atom.

In inorganic chemistry, many metal ions are described as trivalent when they exhibit a +3 oxidation state. Common examples include aluminum(III) (Al3+), iron(III) (Fe3+), chromium(III) (Cr3+), and vanadium(III) (V3+). Trivalent species influence the charge balance and coordination chemistry, often forming oxides, hydroxides, or complex ions; in many contexts the +3 state coexists with other oxidation states under different conditions.

In graph theory, a trivalent, or 3-regular, graph is a graph in which every vertex has degree three. Trivalent graphs arise in network design and theoretical studies.

In immunology and vaccinology, trivalent refers to vaccines containing three antigens or strains, such as historical trivalent influenza vaccines that included two influenza A strains and one B lineage. Many vaccines have since shifted to quadrivalent formulations with four components.