Question

What is the oxidation number method?

Answer 1

Oxidation number of any compound is defined for any atom of an element in the term of net charge that appears when it presents in a combined state with other atoms. Value of the oxidation number should be negative, positive or zero.

Complete answer:
There are some basic rules which need to be followed for determining the oxidation number of any atom of any element.
The oxidation number of an element is considered as zero when it is present in its elementary state or in its allotropic form.
Example- oxidation number of ${H_2},{O_2},B{r_2},{P_4}$ is zero.
The oxidation number of an element in the form of ion is equivalent to the charge present on an atom.
Example- oxidation number of ${K^ + }$ is $1$ , $A{l^{ + 3}}$ is $3$ .
In a compound containing metal as well as non-metal, oxidation number of metals is always positive and non-metal is always negative.
Example- oxidation number of $N{a^ + }$ is $1$ and $C{l^ - }$ is $- 1$ .
In a compound containing only non-metallic atoms, the oxidation number of a high electronegative atom has a negative oxidation number.
Example- oxidation number of $Cl$ in $HCl$ has negative oxidation number $- 1$ .
Oxidation number of Hydrogen is always $1$ except in the case of hydrides.
Oxidation number of Oxygen is always $- 2$ , except during the formation of peroxides, superoxide.
For a neutral element, the sum of the oxidation number of all the atoms is zero.
For a charged element, the sum of oxidation number of all the atoms is equal to total charge on the ion.

Note:
With the use of the concept of electron transfer we can explain the redox reaction in the case of ionic substance and hence we calculate oxidation number of compounds. But the concept of electron transfer is not applicable in the case of covalent compounds and hence we are not able to calculate oxidation number.