halogen means any of the chemical elements fluorine, bromine,iodine,and astatine.The halogens or halogen elements are a series of nonmetal elements from Group 17 of the periodic table, made up by fluorine(F), chlorine(Cl), bromine(Br), iodine(I), and astatine(At). The undiscovered element 117, temporarily named ununseptium, may also be a halogen. Like all other groups in the periodic table, halogens also follow trends. Their melting and boiling points increase down the group.