Reduction and oxidation

The reduction corresponds to the gain of an electron for an atom, ion or molecule. Instead oxidation is a reaction where the atom, ion or molecule loses electrons.

DefinitionReduction is the gain of electrons in a molecule, atom, or ion.Oxidation is the loss of electrons in a molecule, atom, or ion.
Agents involvedThe oxidizing agent is the one that traps the electrons and the oxidized one that loses them.The reducing agent is the one that provides the electrons and the reduced agent is the one that gains the electrons.
ExamplesOxidation of methanol to formaldehyde:


Silver formation from silver ions.


The reduction

The reduction is the gain of electrons, either by a molecule, an atom or an ion (atom in each pole of the electrolyte). So, an element is reduced when in a certain reaction it gains electrons. And that can be verified by the decrease in the oxidation state (reduction and oxidation are processes that occur simultaneously). Therefore, the lower the oxidation state of an atom, the greater its reduction.

The word reduction comes from the Latin reducto meaning “to restore.”

A fairly simple example is the change of copper ion, with oxidation state 2+, going to solid copper, with oxidation state 0. The formula is as follows:

Cu 2+ (ac) + 2e   → Cu (s)

Examples of reduction reactions

  • Molecular oxygen gains four electrons when it is transformed into an oxide ion:

2 (g) + 4e  → 2O 2-

  • Here is another example of the formation of silver from silver ions:

Ag + (ac) + e  → Ag (s)


Oxidation is the loss of electrons in a molecule, atom, or ion . An element oxidizes when in its reaction it loses electrons and it is verified precisely by the increase in the oxidation state of the atom. The higher the oxidation state in an element, the lower its reduction will be as a consequence.

Antoine Lavoisier was the French scientist who used the word “oxidation” in a work, in the 18th century. This brilliant Frenchman was the one who understood the identification of air oxygen, gradually losing place to the phlogiston theory, which explained combustion and other phenomena.

An example of oxidation is given by magnesium which reacts with oxygen to form magnesium oxide.

2Mg(s) + O2(g)→ 2MgO(s)

Examples of oxidation reactions

  • The magnesium atom loses two electrons and becomes a magnesium ion.

Mg(s)→Mg2+(s) +2e

  • The transformation of alcohol into vinegar is an oxidation reaction.

CH 3 CH 2 OH → CH 3 COOH

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