Hi,

It is critical to understand whether an atom loses or gains electrons when combining with other atoms to form compounds. How do we keep track of the electrons that an atom loses or gains? This is accomplished by examining an atom's oxidation number. An oxidation number is a number assigned to a substance's atom. The oxidation number, which can be positive, negative, or zero, indicates whether electrons are lost or gained. In other words, the oxidation number is a number that aids in the tracking of electrons within an atom.

For Instance, Calcium has an oxidation number of +2 and oxygen has an oxidation number of -2.

If the oxidation number is positive, the atom is losing electrons; if it is negative, the atom is gaining electrons. If it is zero, the atom does not gain or lose electrons.

Calcium has a +2 charge, indicating that it has lost two electrons. Because oxygen has a -2 charge, it has gained two electrons.

When an atom loses electrons, its oxidation number increases, and we can say that the atom oxidises. When an atom gains electrons, its oxidation number decreases, implying that the atom is reduced.

You can remember this by thinking of the phrase OIL RIG: Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons).

Hope that helps you