Oxidation NumbersOxidation Numbers

These rules are seriously easy!!

Rule 1

The oxidation number for an atom of any free (uncombined) element

is ZERO.

(eg: Na, Ca, Br2 have an oxidation number of 0 )

Rule 2

The oxidation number for a simple single atom (ie

monatomic) ion is the charge on the ion.

(eg Cl- = -1, Na+ = +1)

Rule 3

In non metal hydrogen containing compounds, oxidation number of

hydrogen is +1 (eg HCl, H2O).

In metal hydrides, the oxidation number of hydrogen is -1 (eg NaH, LiH, CaH2.).

Rule 4

Oxygen is usually assigned an oxidation number of -2 when

combined. (eg H2O, CO2, Na2O)

When combined in peroxides (eg H2O2, or Na2O2) it has an oxidation

number of -1.

When combined with F, ie in F2O, oxygen has an oxidation number

of +2.

Rule 5

The sum of oxidation numbers of all the atoms in the formula for a

neutral compound is ZERO.

Rule 6

The sum of oxidation numbers of a polyatomic ion is the same as the

charge on that ion .