Introduction to Oxidation number

 Introduction

In this lesson, you will learn the basic concept of oxidation numbers, how to calculate them and some basic examples.

Outlines

1. Definition of oxidation number

2. Rules for calculating oxidation number

3. Examples

4. Tips and conclusions

1. Definition of oxidation number

The oxidation number of an element is the charge of its ions in its pure form. It is a way to determine how many electrons should be assigned to each atom for it to achieve a neutral charge. The oxidation number, therefore, is the overall charge of an atom in a compound if all its bonds are ionic. In other words, it's the number of electrons lost or gained by an atom in a compound.

2. Rules for calculating oxidation number

The following rules apply for calculating the oxidation number of any species (atom, ion, or molecule);

1. The oxidation number of atoms in the free state is equal to their charge (zero);

2. The oxidation number of an atom in a neutral molecule is equal to the charge of its ion;

3. The oxidation number of an ionic species is the charge of the specie;

4. The oxidation number of any compound or neutral molecule is equal to the sum of all the charges on each atom in the compound.

For example, if you have two chlorine atoms in a molecule like Cl₂, they each have an oxidation number of +2, and they combine to form one Cl₂. The same concept can be applied to ions: if you have two sodium cations that combine together and form Na+, their combined ionic charge will be +1; however, these two individual cations are still separate entities with their own individual charges (remembering that Na+ has many more electrons than does Cl). In general, when a species has an oxidation number of +1, it is said to be oxidised, and when a species has an oxidation number of -1, it is said to be reduced.

3. Examples

Here are some short examples to help you understand how to calculate the oxidation number of any species.

1. Determine the oxidation number of Na+, Cl-, and Fe2+

   Solutions

   Using rule 3, the oxidation number of Na+ = +1, Cl- = -1, and Fe2+ = +2.

2. Calculate the oxidation number of Na in NaCl.

Solutions

Using rule number 4

• => NaCl = 0

• Substituting for Cl oxidation number as (-1).

• Na+(-1) = 0

• Na = 0+1 = +1

• Therefore, the oxidation number of Na in NaCl is +1.

• Calculate the oxidation number of S in H₂SO₄.

Solutions

Following rule 4, the oxidation number of S can be determined as above (example 2).

• Substituting for H oxidation number as (+1), that of O as -2

• (+1x2)+S+(-2x4) = 0

• S+(-6) = 0

• S= 0+6= +6

• Therefore, the oxidation number of S in H₂SO₄. is +6.

4. Conclusion

The oxidation number is the overall charge of an atom in a compound if all its bonds are ionic. The oxidation number is the overall charge of an atom in a compound if all its bonds are ionic. It is a way of describing the charge on an atom in a compound. The oxidation state of an element is defined as how many electrons it has lost or gained since its creation (i.e., formation). The oxidation number of an element is equal to the sum of the charges on each atom in its molecule.