Redox

Redox (shorthand for reduction/oxidation) describes all chemical reactions in which atoms have an increase or decrease in oxidation number (oxidation state).^[1]

Reduction
Oxidant + e^– ⟶ Product
(Electrons gained; oxidation number decreases)

Oxidation
Reductant ⟶ Product + e^–
(Electrons lost; oxidation number increases)

The two parts of a redox reaction

An oxidation number is a number assigned to an element in chemical combination that represents the number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound.

The term redox comes from the two concepts of reduction and oxidation. It can be explained in simple terms:

Oxidation describes the loss of electrons by a molecule, atom or ion
Reduction describes the gain of electrons by a molecule, atom or ion

Whether an electron is gained or lost can be easily memorised by the abbreviation OIL RIG, which stands for, "Oxidation Is Loss," or losing electrons, and "Reduction Is Gain," or gaining electrons. Redox reactions can also happen by sharing electrons to form a product by covalent bonding.

In an oxidation reduction reaction, the cation gives an electron to the anion because both ions will have a different charge to attract each other with. In an oxidation reduction reaction, the oxidizing reagent pulls an electron from the other atom to have a net positive charge. The reducing reagent gives an electron to have a net negative charge. However, there are exceptions.^[2]

Chemical process

Redox is a chemical process. It can be described in chemical formulas. This example describes the process that occurs in a blast furnace, where iron (Fe) reacts with carbon (C):