Fluorine compounds have a variety of uses. They are added to toothpaste and to water supplies in order to combat tooth decay, although excessive amounts can prove damaging. Chlorofluorocarbons are no longer used so widely as aerosol propellants because of their harmful effect on the ozone layer. Uranium fluoride is used in the generation of nuclear power.
Chlorine is used in the manufacture of disinfectants which are added to water supplies and to swimming pools in order to kill bacteria. Further applications include the production of bleaches used by the paper and textile industries. The use of chlorofluorocarbons has already been mentioned.
The principal industrial use of bromine is in the form of ethylene dibromide, which is used as a scavenger for lead in leaded petrol, although environmental concerns have reduced the demand for this compound. The light-sensitive silver bromide is valuable in photography. Other bromine compounds are used as fire retardants and insecticides, and, like other halogens, they are also employed in the sanitation of water.
Iodine is added to table salt in areas where a natural deficiency of the element has resulted in enlargement of the thyroid gland. Like chlorine, it is also used in disinfectants (all the halogens are poisonous, and so tend to be suited to uses of this kind), and potassium iodide is employed in photography.
Astatine, the rarest of all elements found in nature (it exists only as a short-lived member of a decay series) has no uses.
