How rust is formed?

The exposure of iron (or an alloy of iron) to oxygen in the presence of moisture leads to the formation of rust. This reaction is not instantaneous, it generally proceeds over a considerably large time frame. The oxygen atoms bond with iron atoms, resulting in the formation of iron oxides. This weakens the bonds between the iron atoms in the object/structure.

The reaction of the rusting of iron involves an increase in the oxidation state of iron, accompanied by a loss of electrons. Rust is mostly made up of two different oxides of iron that vary in the oxidation state of the iron atom. These oxides are:

1. Iron(II) oxide or ferrous oxide. The oxidation state of iron in this compound is +2 and its chemical formula is FeO.
2. Iron(III) oxide or ferric oxide, where the iron atom exhibits an oxidation state of +3. The chemical formula of this compound is Fe₂O₃.