Example Three

What is the oxidation number of Iron in Fe₂O₃?

SOLUTION: Since Fe₂O₃ is a compound, we are at the third box in the chart. Let's look at this one step-by-step.

1. Oxygen atoms usually have an oxidation number of -2. Since there are 3 oxygen atoms, the total is -6 (3 X -2 = -6).
   
   
2. To counter the -6, the total for the iron atoms must be +6.
   
   
3. Since there are only two iron atoms, each iron atom must have a +3 oxidation number(2 X +3 = +6).

Click here for a drawing that illustrates the solution.