Fluorine is the most active of all the elements, and it reacts with nearly all other chemical elements. It is a greenish-yellow gas that is poisonous and very corrosive, and it has an irritating odor similar to that of chlorine. Fluorine belongs to the halogen group of elements. It has the smallest atoms and forms the strongest chemical bonds of all the halogens. Because of its great chemical activity, fluorine is very difficult to handle, and it must always be kept in a sealed, moisture-free container to prevent an explosive reaction with moisture. Many metals and other materials, such as wood and asbestos, spontaneously ignite and burn when they are placed in fluorine.
The compounds of fluorine are called fluorides, and many are useful to man. For example, hydrogen fluoride, a colorless gas with an irritating odor, is used to etch glass, and sodium fluoride is used as an insecticide. To prevent enamel decay in teeth, many dentists apply fluorides to the teeth; many communities add fluorine compounds to their drinking water.
Fluorine is commercially produced by the electrolysis of mixtures of hydrogen fluoride, HF, and molten potassium fluoride,