What is the oxidation number of iron in Fe3O7 ?
Oxidation numbers are calculated through a set of rules. Oxygen is an atom that has only 3 possible Oxidation numbers:
- If Oxygen is bonded to itself (Mainly in
#O_2#) then it has an Oxidation number of 0. This is true of any atom that bonds to itself with few exceptions.
- If Oxygen is in the form of Peroxide
#O_2^-2#then it will have an oxidation number of -1.
- In all other cases Oxygen will have an Oxidation Number of -2.
Since your molecule has Iron bonded to Oxygen and that Oxygen is not in the form of Peroxide. It follows that each Oxygen has an Oxidation number of -2.
That gives all of the Oxygen a cumulative Oxidation Number of -14. All molecules must have a Net Oxidation Number equal to their charge (in this case 0). Meaning that the 3 Irons must add up to +14 cumulatively.
Simple division then leads you to determine that the +14 distributed across 3 Iron atoms will have an Oxidation number of