6.4 - Redox

Oxidation and reduction as electron transfer

• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• Remember: OIL RIG (Oxidation Is Loss, Reduction Is Gain).
• Electrons are transferred from one substance to another, so oxidation and reduction always occur together in a redox reaction.

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Worked example - Sodium and chlorine

2Na + Cl₂ → 2NaCl

• Each sodium atom starts neutral and becomes Na⁺ (loses one electron), so sodium is oxidised.
• Each chlorine atom starts neutral and becomes Cl^- (gains one electron), so chlorine is reduced.

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Identifying oxidation and reduction from charges

• An atom that becomes a positive ion loses electrons: oxidised.
• An atom that becomes a negative ion gains electrons: reduced.
• A positive ion that becomes an atom gains electrons: reduced.