How are oxidation number determined and used?

Answer 1

This may best be demonstrated by example:

Here are two forms (read: oxidation numbers) of iron, as FeO and Fe2O3. Because we know oxygen has a -2 charge per atom, the oxidation number of Fe in FeO is II. As for Fe2O3, we know that the oxidation number of Fe is III; there is no charge on the compound, so the two iron molecules must equally offset the -6 charge from the three oxygen atoms.

Oxidation numbers are written as roman numerals. You would write these two forms of iron oxide as iron(II) oxide and iron(III) oxide, respectively. Oxidation states are the (+) or (-) charges written as a superscript.

Answer 2

The oxidation number of an element is determined based on the number of electrons it gains or loses in a chemical reaction. It is used to track the flow of electrons in a reaction, identify the element that is oxidized or reduced, and balance chemical equations. Oxidation numbers help in determining the overall charge of a compound and in predicting the reactivity of elements.