To form a chemical bond with another atom, the entire number of electrons that an atom can either lose or gain or share is known as oxidation number. An oxidation number is assigned to those atoms participating in the oxidation-reduction reaction, which mainly shows their ability to donate, share electrons and acquire. The meaning of oxidation can be determined as the number allotted to elements in chemical mixtures. The changes occurring in the redox reaction can be referred to as the oxidation number or state.

Oxidation number

The oxidation number, also known as oxidation state, is the state of an atom in a chemical compound that provides insight into the number of oxygen electrons reduced. It also describes the extent of oxidation of the atom. The oxidation states can also be defined as the hypothetical charge that can be held by that atom if all its bonds with the other atoms are ionic.

Oxidation State

It implies the degree of oxidation in a chemical compound for an atom. These are generally denoted by integers, either positive, negative, or zero.

Atoms/molecules and ions that consist of constant oxidation state or number: 

1. For the neutral atoms or molecules, the net charge is zero. Therefore, their oxidation state is also zero.

For example: 

Let’s say the oxidation state of elemental atom-like magnesium, iron, and sodium is zero. Likewise, net oxidation of neutral molecules like water, potassium permanganate, oxygen methane, chlorine is also zero.

2. The net charge of the ion is similar to the oxidation state of charged ions. Therefore:

• For all alkali metal ions, the oxidation number is constantly +1.

• For all alkaline earth metal ions, the oxidation number is constantly +2.

• For all boron family metal ions, the oxidation number is constantly +3.

• Hydrogen in protons: Oxidation number is +1, and oxidation number of hydrogen in hydride is -1.

• Oxygen in oxide ion: oxidation number is -2, and oxidation number of oxygen in peroxide ion is -1.

How to find the oxidation number of an atom?

The oxidation number or oxidation state of an atom or ion is the total number of atoms or ions that the molecule has either gained or lost, comparable to the neutral atom.

The group 1, 2, and 3 electropositives lose a particular number of electrons and always have consistent positive oxidation numbers as oxidation state.

The oxidation number or oxidation state of an atom or ions in a molecule or ion is calculated by:

• Adding up the consistent oxidation number or state of atoms/molecules or ions that are restrained.

• Next, by correlating the total oxidation state of a molecule or ion to the total charge of the ion or molecule.

The oxidation number of nitrogen:

The oxidation number of nitrogen can be anything in between -3 to +5. The oxidation number of nitrogen is mainly dependent on the ion or compound in which we find nitrogen. Generally, the most common oxidation number is -3, +3, and +5.

A few examples of nitrogen compounds and the oxidation states of N are:

• Lithium nitride (Li3N); Oxidation state: -3.

• Ammonia (NH3); Oxidation state: -3.

• Hydrazine (N2H4; Oxidation state: -2.

• Diimide (N2H2); Oxidation state: -1.

• Dinitrogen (N2); Oxidation state: 0.

• Nitrous oxide (N2O); Oxidation state: +1.

• Nitric oxide (NO); Oxidation state: +2.

• Nitrogen dioxide (NO2); Oxidation state: is+3.

• Dinitrogen tetroxide (N2O4); Oxidation state: is +4.

• Nitrate (NO3); Oxidation state: is +5.

Important facts of oxidation numbers:

1. The oxidation number can either be positive or negative.
2. Metals always release electrons to form positive ions. Thus, they always form a positive oxidation number.
3. There are various non-metals like phosphorus, sulfur, and chlorine. Here, they can form both positive as well as negative oxidation numbers.

More than one oxidation number of an element:

1. Many elements can show oxidation states that are more than one. Especially the elements of the d block show this behaviour.

For example:

1. Chlorine can show oxidation numbers like -1 , 0 , +1 , +3 , +5 , +7
2. Manganese can show oxidation numbers like 0 , +2 , +4, +7

3. When an element does not form a compound:

• So when an element doesn’t form a compound, its oxidation number is 0.
• For example, the oxidation number of Au is 0.

4. While an element is combined with the same kind of element:

1. When an element is combined with a similar kind of element, its oxidation number becomes 0.
2. For example, the oxidation number of Bromine (Br) in Br2 is 0.

The oxidation numbers list:

Conclusion

When the oxidation number of an atom is increased, it gives the outcome of oxidation. At the same time, a decrease in the oxidation number of an atom gives the outcome of reduction. Therefore, the analysis of redox reaction is done by the change in oxidation number to find out what is being oxidised and what is being reduced.