Radicals are formed when a molecule or atom has an unpaired electron, making it highly reactive. The formation of radicals usually involves breaking a covalent bond in such a way that each atom gets one electron from the bond instead of both. This process is called homolytic bond cleavage.
Here’s a clear breakdown:
1. Homolytic Fission
- A covalent bond between two atoms breaks evenly.
- Each atom takes one electron from the shared pair, forming two radicals.
- Example: If a bond between two chlorine atoms breaks, each chlorine ends up with an unpaired electron.
2. Initiation by Energy
Radicals are often formed by supplying energy to the molecule, which can come from:
- Heat – high temperatures can break bonds homolytically.
- Light (UV radiation) – photons provide enough energy to break bonds.
- Chemical initiators – certain compounds (like peroxides) decompose to form radicals.
3. Common Sources
- Halogens under UV light (used in free radical halogenation)
- Organic peroxides
- Molecules with weak bonds (like O–O in peroxides or Cl–Cl in chlorine gas)
Key point: Radicals are highly reactive because they have an unpaired electron and tend to react with other molecules to pair up that electron.