Electronic interpretation of oxidation and reduction

From the above reactions, it can be seen that the oxidation-reduction reactions involve transfer of electrons from one species to another. Thus, the oxidation-reduction reactions may also be defined as follows.

Oxidation is a chemical process in which there is a loss of electrons. The species, which gets oxidized becomes more positive or less negative, e.g.,

Reduction is a chemical process in which there is a gain of electrons. The species, which gets reduced becomes more negative or less positive, e.g.,

Oxidizing agent is the species, which accepts electrons, e.g.,

Reducing agent is the substance, which loses electrons, e.g.,

Oxidation and Reduction (Electron Transfer Process)

Magnesium when burnt in air gives magnesium oxide in accordance with the reaction,

Here, magnesium combines with oxygen to form magnesium oxide, i.e., oxygen is added to magnesium. According to the classical concept of oxidation and reduction, the addition of oxygen to magnesium is termed as the oxidation of magnesium.

The formation of magnesium oxide on the basis of the electronic configurations of magnesium and oxygen can be explained as follows:

Magnesium oxide (MgO) consists of Mg²⁺ and O^2-.

This means that during the formation of MgO, Mg is converted into Mg²⁺ and O into O^2-. This is possible only when a magnesium atom (Mg) loses two electrons to form Mg²⁺ and an atom of oxygen (O) gains two electrons to form oxide ion (O^2-). The following reactions should occur.

In the overall reaction between magnesium and oxygen as electron does not appear either on the reactant-side nor on the product-side, the number of electrons lost by magnesium must be equal to the number of electrons gained by oxygen. In this way the number of electrons are balanced. To balance electrons, the first reaction is multiplied by 2.

Then, adding the other two equations one obtains,

Thus, two electrons are transferred from a magnesium atom to an oxygen atom in the reaction between magnesium and oxygen. This electron-transfer process is possible only when one of the species is capable of losing while the other is capable of gaining an electron, both being present in the reaction. The loss and the gain of electrons occurs simultaneously.

The process involving loss of electrons is termed as oxidation, while that involving gaining of electrons is termed reduction. Therefore, oxidation and reduction reactions involve electron-transfer from one reactant to another.

Such reactions in which electrons are transferred from one reactant to another are called "redox reactions" involving both oxidation and reduction.

For example,

Problem

1. In the following reaction, label the oxidizing agent and the reducing agent.

Solution