Free Radical Definition

Chemistry Glossary Definition of Free Radical

Diagram of free radical

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An atom or molecule with an unpaired electron. Because they have a free electron, such molecules are highly reactive.


Singlet oxygen, molecules with a free hydroxy group (-OH)


Free radicals are capable of starting rapid chain-reactions that destabilize the ions in other nearby molecules generating more free radicals.

In biological systems, free radicals are deactivated by anti-oxidants, uric acid, and certain enzyme activities.

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Helmenstine, Anne Marie, Ph.D. "Free Radical Definition." ThoughtCo, Aug. 28, 2020, Helmenstine, Anne Marie, Ph.D. (2020, August 28). Free Radical Definition. Retrieved from Helmenstine, Anne Marie, Ph.D. "Free Radical Definition." ThoughtCo. (accessed June 9, 2023).