State the rules to determine the oxidation number.
Answers
1. An atom in a pure element or molecule such as H2 has an oxidation number of zero.
2. For ions consisting of a single atom, the oxidation number is equal to the charge on the ion.
3. Fluorine is always -1.
4. Chlorine, bromine and iodine are -1 except in compounds with fluorine or oxygen (both of which have higher electronegativities).
5. The oxidation number of hydrogen is +1 except when bound to a metal (hydrogen is more electronegative).
6. The oxidation number of oxygen is -2.
7. The sum of the oxidation numbers in a neutral compound must be zero.
8. The sum of the oxidation numbers for a polyatomic ion must equal the ion charge.
These rules can be summarized to some extent by giving an atom -1 for any bonded atom of lesser electronegativity, +1 for any bonded atom of greater electronegativity and 0 for any bonded identical atoms.