Glossary
oxidation
Oxidation is the loss of electrons by a species; it always comes with a reduction, in which another species gains them.
Oxidation is the loss of electrons, and reduction is the gain of them. The two always happen together, because an electron that leaves one species arrives at another: whatever is oxidized is oxidized by something that is reduced. An oxidation number is the bookkeeping that tracks this — it rises when a species is oxidized and falls when a species is reduced, which is the opposite of the electrons' charge and the usual way a slip is caught. The older shorthand, "oxygen is added", describes combustion well and the rest poorly; the electron definition covers the cases oxygen never touches, such as a metal displacing another metal out of solution. A reaction in which one species is oxidized and another reduced is called a redox reaction. Keep the direction in sight: losing electrons is oxidation, and the species that does the taking is the oxidizing agent.
Taught in
Related terms
- ionic bond — An ionic bond is the attraction between two oppositely charged ions, formed when one atom gives electrons to another — a metal and a nonmetal, usually.
Source: NIST periodic table and reference data for the atomic masses and half-life figures, NIH PubChem for the substance data, and NIST Special Publication 811 for the unit conventions — the same sources the chemistry guide cites. All three are US federal government material, not subject to copyright in the United States. Every definition, example and calculation above was written for this course; no dictionary or textbook text is reproduced. (NIST and PubChem accessed 2026-10-26; definitions written 2026-10-27)