Radical

From GAWDAwiki

A radical is a molecule or atom which has an unpaired outer electron. It is very reactive because it needs to gain an electron. Radicals may exist independently for short periods during the course of a chemical reaction, such as in the combustion of a fuel gas.^[1]

References

1. http://www.bocindustrial.co.uk/bocindustrial/technical/glossary/a.asp