halogen has definitions from the field of chemistry
[ noun ] (chemistry) any of five related nonmetallic elements (fluorine or chlorine or bromine or iodine or astatine) that are all monovalent and readily form negative ions

Used in print

(Francis J. Johnston and John E. Willard, "The...)

Because of the simplicity of the molecules , isotopic exchange reactions between elemental halogens and the corresponding carbon_tetrahalides would appear to offer particularly fruitful possibilities for obtaining unambiguous basic kinetic data .

It would appear that it should be possible to determine unique mechanisms for the thermal and photochemical_reactions in both the liquid and gas phases and to determine values for activation_energies of some of the intermediate reactions of atoms and free_radicals , as_well_as information on the heat_of_dissociation of the carbon halogen bond .