Actually the free radical of chlorine and the chlorine atom do not have any difference because in the chlorine atom there are 7 electrons in the outermost shell and also in the chlorine radical there are 7 electrons in the outermost shell. But chlorine atom is not produced or chlorine is not found in atomic state but when chlorine molecule is excited by the UV radiation then chlorine free radicals are produced. Free radicals are very reactive and they accelerates the chemical reactions. Though both of them have the same electronic configuration but they are called free radicals not atom because they are not found generally and only produced by UV radiation.