Radicals are any molecule, atom or ion that has an unpaired valence electron or an open electron shell. Radicals are often reactive to other substance that it can contact with or even to form other substance. Reactions of which can be a chain reaction which are related to environmental problem due to degradation of our resources to some extent.
The outermost shell of a radical contains the unpaired electron. Often times you will be able to see a molecule with a single dot in its Lewis structure which indicates that it is a free radical. For example, let us look at the formation of chlorine radical from chlorine gas.
`Cl_2 -> Cl* + Cl*`
The Lewis structure of chlorine radical can be written as:
`:Cl *` . .