Oxidation numbers 

So far we have defined redox (reduction/oxidation) reactions in terms of electron transfer. It is easy to determine the oxidant and reductant in reactions such as in the one below between magnesium and oxygen.
What about reactions that do not involve ions? Reactions such as the formation of water A few rules apply. Rule 1) The oxidation number of all substances in their elemental form is zero.
Rule 2) The oxidation number of all monoatomic(single atom) ions is the charge on the ion. Rule 3) The oxidation number of oxygen is 2. Exceptions are peroxides where it is 1 and where it is +2. Rule 4) Hydrogen is +1 except in metal hydrides where it is 1. Rule 5) In polyatomic ions and molecules the sum of the oxidation numbers of each atom is equal to the charge on the ion or molecule. Example 1)What is the oxidation number of manganese in Mn + 4 X 2
= 1 2) What is the
oxidation number of Cr in
(scan the formula for more
information) 2 X 1 + Cr
+ 4 X 2 = 0 3) What is the
oxidation number of manganese in
(scan the formula for more
information) 2X Mn + 3
X 2 =0 

Exercises. 1) Find the oxidation number
of carbon in
and Scan the formulae for the answer 

