Oxidationsstal

Oxidationsstal, or oxidation state, is a formalism used in chemistry to describe the oxidation level of an atom within a compound. It is a bookkeeping device that helps track electron transfer in redox reactions. The rules commonly used are: the oxidation state of a free element in its standard state is zero; in ions it equals the ion’s charge; the sum of oxidation states in a neutral compound is zero, and in a polyatomic ion it equals the ion’s charge. Typical values include oxygen usually −2, hydrogen +1 (except in metal hydrides), and alkali/alkaline earth metals following their group numbers. Exceptions arise in peroxides, superoxide, and certain fluorides where oxidation states can differ from the simple rules.

Determining oxidation states involves applying these rules in a systematic way. In covalent compounds, electrons may be assigned to the more electronegative atom to reflect electron distribution. For a neutral molecule, the sum of oxidation states is zero; for a polyatomic ion, the sum equals the ion’s charge. Example: in water, H2O, the oxidation states are +1 for each hydrogen and −2 for oxygen, summing to zero. In potassium permanganate, MnO4−, the four oxygens contribute −8, so manganese must be +7 to yield the overall −1 charge.

Applications of oxidationsstal include balancing redox equations, predicting possible reaction pathways, and assigning oxidation numbers in coordination chemistry and organometallics. They are a useful abstraction for electron bookkeeping but do not represent exact charges on atoms, especially in compounds with delocalized bonding or resonance, where oxidation states can be non-integer in some descriptions.

Historically, the concept was developed in the late 19th century as part of the formalism surrounding redox chemistry and electron transfer.