Occasionally, elements may have more than one possible oxidation state. Multiple oxidation states result from a phenomena called variable valence, a situation in which an atom may lose a different number of electrons depending on the situation. Variable valence occurs most often in atoms with incomplete d subshells. By altering their valence state, atoms exhibiting variable valence can achieve other stable electron configurations. For example, manganese will often exhibit the +7 oxidation state in solution to assume the stable electron configuration of argon. Manganese is also often found in solution in the +2 oxidation state, to yield a stable configuration with a half filled set of d orbitals.
