Rules For Assigning Oxidation Numbers

1. Elements have an oxidation number of zero. (Ex: Au, H₂, and S₈ all have oxidation numbers of 0)
   
   
2. Monoatomic Ions (single atom ions) have oxidation numbers equal to their charge. (Ex: Al³⁺ has an oxidation number of +3)
   
   
3. Use the following elements to calculate any remaining oxidation numbers:
   
   
   • Group I and Group II metals always have +1 and +2 oxidation numbers, respectively.
   • Hydrogen usually has a +1 oxidation number.
   • Oxygen usually has a -2 oxidation number.
   • Fluorine always has a -1 oxidation number.

Use the chart on the right to help you remember the order in which to check the atoms.