isovalent

Isovalent describes species that have the same valence, typically the same oxidation state and the same number of valence electrons involved in bonding. The term is used mainly in inorganic chemistry, solid-state chemistry, and mineralogy to describe relationships between atoms or ions that, while sharing the same charge, may differ in size or electronic structure.

In the context of substitution in compounds, isovalent substitution occurs when one ion is replaced by another with the same charge, preserving overall charge balance. For example, in minerals such as olivine, magnesium and iron can substitute for one another because Mg2+ and Fe2+ have the same valence. Similarly, in perovskites or fluorites, divalent cations such as Ca2+, Sr2+, or Ba2+ can occupy the same lattice site isovalently. Isovalent exchange can be used to tune the properties of materials without altering the stoichiometric charge.

It is important to distinguish isovalent from isoelectronic. Isoelectronic refers to species that have the same total number of electrons, which can include ions or neutral atoms with different valences. Isovalent does not guarantee identical chemical behavior; differences in ionic radius, coordination preferences, and electronic structure can give rise to distinct properties.

See also: valence, oxidation state, isoelectronic, substitution, solid solution.