1. Oxidation and reduction

If, during a reaction, a substance loses electrons, it is said to undergo OXIDATION. On the other hand, if a substance gains electrons, it is said to undergo REDUCTION. Such a reaction can be considered to consist of two HALF-REACTIONS.

For example, when magnesium reacts with chlorine, magnesium undergoes oxidation, since it loses two electrons:

In turn, a chlorine molecule undergoes reduction, since it gains two electrons:

The overall reaction between magnesium and chlorine is called a REDOX REACTION (REDuction-OXidation), because electrons are transferred between the reactants, magnesium on the one hand, and chlorine on the other.

The reactants (Mg and Cl2 in this case) are quite complementary in their behaviour: the magnesium supplies electrons to the chlorine. Mg becomes OXIDIZED to the cation Mg2+ , while the Cl2 molecule becomes REDUCED to the anion Cl- . We say that "THE CHLORINE HAS OXIDISED THE MAGNESIUM". It would also be quite correct to say that "THE MAGNESIUM HAS REDUCED THE CHLORINE".

2. Redox reagents

Substances gaining or losing electrons during redox reactions are known as REDOX REAGENTS. Taking the example above, magnesium, which supplies electrons to the chlorine and thus causes its reduction, is called the REDUCING AGENT or REDUCTANT. The chlorine, which accepts electrons from the magnesium and thereby causes its oxidation, is called the OXIDIZING AGENT or OXIDANT.

3. Additional questions