Reduction

Reduction is a chemical process in which a substance gains electrons or decreases its oxidation state. It occurs alongside oxidation in electron-transfer reactions.

Oxidation state: A formal charge assigned to an atom by treating its bonds as ionic. Reduction is identified by a decrease in an atom’s oxidation state.
Electron: A negatively charged subatomic particle found in atoms and chemical bonds. Electron gain is the literal basis of reduction in electron-transfer reactions.
Smelting: The extraction of a metal from its ore by heating and chemical reduction. Smelting reduces metal compounds to produce elemental metals.
Oxidation: A chemical process in which a substance loses electrons or increases its oxidation state. Oxidation is the paired opposite of reduction in redox chemistry.
Redox reaction: A chemical reaction involving coupled oxidation and reduction. Reduction is one half of every redox reaction.
Chemical bond: An attractive interaction that holds atoms or ions together in a substance. Bond polarity helps assign oxidation states when electron transfer is not explicit.
Electrolysis: The use of electric current to drive a nonspontaneous chemical reaction. Reduction occurs at the cathode during electrolytic reactions.
Acid–base reaction: A reaction involving proton transfer or, more broadly, electron-pair donation and acceptance. Acid–base reactions need not involve the electron transfer that defines reduction.
Electron transfer: The movement of electrons from one atom, molecule, or material to another. Gain of electrons is the defining microscopic change in reduction.
Electronegativity: A measure of an atom’s tendency to attract shared electrons in a chemical bond. Oxidation-state rules assign bonding electrons to the more electronegative atom.

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