Oxidation state refers to the number of electrons added to or removed from an element. Sodium metal, for example, has an oxidation state of 0 in the elemental state. But when it gives up its one valence (outer) electron (symbolized by e-), it becomes a sodium ion with an oxidation state of +1. Iron is another example. It can lose two electrons, forming an oxidation state of +2; or it can lose 3, forming an oxidation state of +3.
The oxidation state determines the number of atoms of other elements that can bind to the atom.
All elements have an oxidation state of 0.
- oxygen has an oxidation number -2 in most of its compounds except peroxides where it has an oxidation number -1.
- hydrogen has oxidation state +1 in most compounds except with electropositive elements. ex: Na.
- alkali earth metals have oxidation state +2
- alkali metals have oxidation state +1