What about the chlorine, the chlorine has a minus one oxidation number here, it has a minus one oxidation number here, it was neutral relative to the redox reaction, anyway I think you get the point now, and you can do this with a bunch of reactions, but this will give you a little more insight of actually whats going on and who's gaining and who's losing electrons and in the future it will also help us think about alot of the structures of molecules. 