Oxidation
The loss of electrons by a species, accompanied by an increase in its oxidation number.
Formula / equation
M → Mⁿ⁺ + n e⁻
Unit
Dimensionless
In depth
Historically defined as gain of oxygen or loss of hydrogen, oxidation is now understood generally as electron loss, which covers reactions involving neither element. Oxidation always occurs at the anode and can never happen without a simultaneous reduction somewhere else.
Examples in the real world
Zn → Zn²⁺ + 2e⁻ in a battery; iron rusting; ethanol oxidising to ethanal in the liver.