Rules for Determining Oxidation Numbers
1. The sum of the oxidation numbers for all atoms add up to the charge on the
molecule or ion. The net charge (oxidation number) of any element or
compound is zero.
2. Group I (alkali metals) and Group II (alkali earth metals) have oxidation
numbers equivalent to their ionic charge which equals +1 and +2 respectively.
Group 13 metals are +3.
3. The oxidation number for hydrogen is +1 and the oxidation number for
fluorine is –1.
4. The oxidation number for oxygen is –2.
5. The oxidation number of a halogen (Group 17) is –1.
6. The oxidation number for a nonmetal in Group 16 is –2.
The oxidation number rules makeup a hierarchy, meaning that rule 1 is the most
important and rule 6 is the least important. If two rules conflict, the rule closest to the
top of the list is obeyed and the other is ignored.