Electrons are most stable when they exist in pairs within chemical bonds. The odd number of electrons leaves the free radical electronically unstable. It reacts rapidly to find a partner for its lonely electron.
The radical often steals an atom from a nearby stable molecule. Hydrogen is a frequent target because its bonds are easy to break. Sometimes, two radicals simply crash together and share their single electrons.
Most free radicals form through a process called homolytic bond cleavage. In this reaction, a normal covalent bond splits perfectly down the middle. Each broken fragment keeps one electron from the original shared pair.
Intense heat, ultraviolet light, or radiation usually trigger this equal split. Once formed, these unstable particles often start a runaway chain reaction. One radical reacts to create a new one, spreading the chemical change.
These radical chains drive many very important real-world chemical processes. They power the fiery combustion reactions inside modern car engines. They also break down protective ozone molecules high in the atmosphere.
Chemists use them to link small molecules into long industrial plastics. In biology, certain radicals are known as reactive oxygen species. These can damage fats, proteins, and DNA structures inside our cells.
This cellular damage contributes directly to aging and oxidative stress. However, our bodies also use controlled radical reactions for good purposes. Specific enzymes rely on them to carry out normal cellular metabolism.