What is Oxidation Number?
In ionic bonds, electrons are shared between atoms. For example, in NaCl, the Sodium atom shares its outer shell electron with Chlorine: This completes and stabilizes the outer Chlorine shell, and leaves Sodium with a stable and complete inner p shell. Sodium, now effectively short an electron, has a pseudocharge of +1; Chlorine, effectively gaining an electron, has a pseudocharge of -1. The pseudocharge is what we call the Oxidation number. Determining the oxidation number of an atom before and after a chemical reaction lets us know whether its been oxidized or reduced. If the oxidation number increases (becomes more positive), the atom has been oxidized; if it decreases, it has been reduced. This also tells us which way the electrons will flow. In water, for example, each hydrogen atom shares its electron with the oxygen atom, resulting in a slightly polar molecule: Oxygen has an oxidation number of -2 and hydrogen has an oxidation number of +1. Net charge = ___. (Why?) Sample Proble
