Free Radical
Definition and meaning of Free Radical in chemistry.
A free radical is an atom, molecule, or ion that contains at least one unpaired electron in its outer shell, making it highly reactive and typically short-lived.
In more detail
The unpaired electron leaves the species electronically unstable, so free radicals react rapidly to pair that electron, often by abstracting an atom (commonly hydrogen) from another molecule or by combining directly with another radical. Most radicals form through homolytic bond cleavage, in which a covalent bond splits so each fragment keeps one electron, frequently triggered by heat, light, or ionizing radiation. Radical chain mechanisms drive important processes including combustion, atmospheric ozone chemistry, and industrial polymerization. In biology, radicals such as reactive oxygen species can damage lipids, proteins, and DNA, contributing to oxidative stress, though enzymatic radical reactions also support normal metabolism.
Key facts
| General notation | R• (dot denotes unpaired electron) |
|---|---|
| Field | General Chemistry |
| Common formation route | Homolytic bond cleavage |
| Key property | Unpaired electron; high reactivity |
Exposing chlorine gas to ultraviolet light causes homolytic cleavage, Cl2 → 2 Cl•, generating chlorine radicals that initiate the free-radical chain halogenation of methane to form chloromethane.
Frequently asked questions
Why are free radicals so reactive?
Their unpaired electron is energetically unfavorable, so reacting with another species lets the electron pair up, stabilizing the system.
Are free radicals always harmful to living cells?
Not always; while reactive oxygen species can damage DNA and proteins, controlled radical reactions also occur in normal enzymatic processes and metabolism.