Find the oxidation number of the following compounds.
HClO4, NH^4+, NaMnO4
The oxidation number of an atom in a compound is the charge that atom would have if the compound was composed of ions.
1. HClO4:
H has an oxidation number of +1 (group 1A).
Cl has an oxidation number of -1 (group 7A).
Oxygen usually has an oxidation number of -2, except in peroxides and compounds with more electronegative elements, such as fluorine, in which case it has a positive oxidation number.
In this case, since Cl is more electronegative than O, it carries the oxidation number of -1, which makes O have an oxidation number of + 7.
2. NH4+:
N has an oxidation number of -3 (group 5A).
In NH4+, since the overall charge of the compound is +1, each hydrogen atom must have an oxidation number of +1.
3. NaMnO4:
Na has an oxidation number of +1 (group 1A).
MnO4 has an overall charge of -1. Since there is only 1 Mn atom, the sum of oxidation numbers must be equal to -1. Oxygen has an oxidation number of -2, so that leaves Mn with an oxidation number of +7.
Therefore, the oxidation numbers are:
1. HClO4: H(+1), Cl(-1), O(+7)
2. NH4+: N(-3), H(+1)
3. NaMnO4: Na(+1), Mn(+7), O(-2)