Hapetusastetta

Hapetusastetta, known in English as oxidation state, is a formalism used in chemistry to describe the electron accounting of atoms within molecules and ions. It indicates how many electrons an atom is considered to have gained, lost, or assigned to itself in comparison with its elemental form. Oxidation states are used to balance redox equations, classify redox reactions, and describe electron transfer in inorganic and organometallic chemistry. Values are typically integers and can be positive, negative, or zero; for a neutral compound the sum of oxidation states is zero, while in an ion the sum equals the ion’s charge.

Assignment of oxidation states follows a set of conventions. A free element has oxidation state 0. A monoatomic ion has an oxidation state equal to its charge. Hydrogen is usually assigned +1, and oxygen -2 in most compounds. Halogens are typically -1 unless bound to a more electronegative element, while alkali metals have +1 and alkaline earth metals +2. The overall oxidation states in a compound must balance to the compound’s charge.

Examples illustrate the concept. In sodium chloride (NaCl), sodium is +1 and chlorine is -1. In water (H2O), hydrogen is +1 and oxygen is -2. In potassium permanganate (KMnO4), K is +1, Mn is +7, and oxygen is -2 per O atom, balancing to the neutral compound.

Limitations exist: oxidation state is a formal bookkeeping device and may not reflect the true electron distribution, especially in covalently bonded or delocalized systems. In transition-metal chemistry, ligands and non-innocent species can complicate assignments, and fractional oxidation states can appear in averaged descriptions.