oxidationstate

Oxidation state, or oxidation number, is a formalism used in chemistry to describe the degree of oxidation of an atom within a compound or ion. It serves as a bookkeeping tool to track electron transfer in redox reactions and to balance chemical equations.

Rules for assigning oxidation states include: the elemental form has oxidation state 0; a monoatomic ion has the ion’s charge; the sum of oxidation states in a neutral compound is 0 (and in an ion it equals the ion’s charge). Fluorine is always -1 in compounds; oxygen is normally -2, except in peroxides where it is -1 and in compounds with fluorine where it can be positive; hydrogen is usually +1, except in hydrides where it is -1; alkali metals are +1 and alkaline earth metals +2; halogens are usually -1 but may be positive in oxoanions or when bonded to more electronegative elements.

Examples illustrate the assignments: NaCl has Na +1 and Cl -1; H2O has H +1 and O -2; CO2 has C +4 and O -2; SO4^2- has S +6; MnO4^- has Mn +7; Fe2O3 has Fe +3.

Oxidation state is a formal tool rather than a literal map of electron density. It is widely used to balance redox equations, describe electron-transfer processes, and name inorganic compounds, especially in coordination chemistry where metals are given oxidation-state indicators (for example, iron(II) or iron(III)).

In practice, oxidation states provide a common framework for comparing redox behavior, though covalency and resonance can cause deviations in actual electron distribution.