The Halogens - Properties . The halogens are the only group of the Periodic Table which have solid , liquid and gaseous elements at room temperature . Fluorine is an extremely reactive pale yellow gas .
Chlorine is a reactive yellow-green gas .
Bromine is a less reactive red-brown liquid . Iodine is a still less reactive dark grey solid. When iodine is heated , it Sublimes to become a gas with a purple vapour .