Thus Na + has oxidation number +1, Fe 3+ has oxidation number +3, F - has oxidation number of -1 and S 2- has oxidation number of -2. First of all, charged mono atomic ion has oxidation number equal to its charge.There are several simple rules used for assigning oxidation numbers to every atom present in any compound: These charges - assigned to individual atoms - are called oxidation numbers, just to remind you that they don't reflect real structure of the reagents. The general idea behind the oxidation numbers (ON) method for balancing chemical equations is that electrons are transferred between charged atoms. They were invented to help in charge accounting needed when balancing redox reaction equations, but they don't refer to any real life chemical concept. Oxidation numbers method of balancing redox reaction equationsīefore we will get to explanation very important disclaimer: oxidation numbers don't exist.