Oxidation numbers in ionic species

Inorganic chemistry may be divided into four types of reaction acid/base, precipitation, complexation and redox. It is when considering redox reactions that oxidation numbers are used to greatest advantage. This is particularly true when ensuring that a reaction equation has been properly balanced, i.e. that the same amount of reduction as oxidation has taken place. 

In simple ions the oxidation number represents the notional whole charge that resides on that ion. So in NaCl, the sodium has an oxidation number of+1, while the chlorine has an oxidation number of-1. In MgCl2, the chlorine still has an oxidation number of-1, but the magnesium has an 

In Fe203, the oxygen has an oxidation number of-2, while the iron has an oxidation number of 

In complex ions such as nitrate, N03, and sulphate, S042-, this charge polarisation is 

In inorganic chemistry the oxidation number is calculated by applying a number of simple rules  

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