Redox reaction and example using electron gain and electron loss

• Oxidation: The process of losing electrons. The species that loses electrons is said to be oxidized.
• Reduction: The process of gaining electrons. The species that gains electrons is said to be reduced.

Example: The reaction between magnesium metal and oxygen gas to form magnesium oxide.

$$2\text{Mg(s)} + \text{O}_2\text{(g)} \to 2\text{MgO(s)}$$

Let's break this down into half-reactions showing electron transfer:

• Oxidation (electron loss): Magnesium atoms lose two electrons each to become magnesium ions.

  $$\text{Mg(s)} \to \text{Mg}^{2+}\text{(s)} + 2\text{e}^-$$

  Magnesium is oxidized.

• Reduction (electron gain): Oxygen molecules gain four electrons (two electrons per oxygen atom) to become oxide ions.

  $$\text{O}_2\text{(g)} + 4\text{e}^- \to 2\text{O}^{2-}\text{(s)}$$

  Oxygen is reduced.

In this reaction, magnesium loses electrons (is oxidized), and oxygen gains electrons (is reduced). Therefore, it is a redox reaction.