valencechange

Valencechange refers to a change in the valence of an atom as it participates in a chemical process. In practice, this most often means a change in oxidation state, the formal number of electrons assigned to the atom according to standard oxidation-number rules. Valence changes occur during redox reactions, where one species is oxidized (loses electrons) and another is reduced (gains electrons). They can also arise when bonds are formed or broken in a way that redistributes electron density and alters the formal valence, though the underlying electron distribution may be more complex than simple bookkeeping.

In redox chemistry, valence changes are tracked by oxidation states. For example, iron metal can be oxidized from Fe(0) to Fe(II) or Fe(III) in rust formation, while permanganate can be reduced from Mn(+7) in MnO4− to Mn(+2) in Mn2+. Carbon compounds illustrate valence changes during oxidation: carbon in elemental form has an oxidation state of 0 and can reach +2 in CO and +4 in CO2. Valence changes underpin the energetics and mechanisms of many processes, including combustion, corrosion, respiration, and electrochemical reactions.

Valencechange is a central concept in redox chemistry, catalysis, and energy storage, where the ability of atoms or ions to change their oxidation state enables electron transfer and catalytic cycles. It is typically quantified using oxidation numbers, though these are formal charges that aid bookkeeping rather than direct measures of electron distribution. Related concepts include oxidation state, redox reactions, electron transfer, and coordination chemistry.