Fluorine is the lightest nonmetal of the halogens, Group VIIA. Other members of the group are chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Agricola described the use of fluorspar (calcium fluoride, CaF2) as a flux for metallurgy in De Re Metallica in 1529.
As early as 1670 Schwandhard found that glass was etched when exposed to fluorspar treated with acid. Scheele and many later investigators, including Davy, Gay-Lussac, Lavoisier, and Thénard, experimented with hydrofluoric acid, some experiments ending in tragedy.
Elemental fluorine was finally isolated in 1886 by Moissan after nearly 74 years of continuous effort by a variety of chemists. The gas was prepared by electrolysis of a solution of hydrogen fluoride containing potassium hydrogen (acid) fluoride in vessels of metal or transparent fluorspar.
The name is derived from the Latin word fluore for flow or flux since fluorspar, calcium fluoride, was used in the smelting of metals to make the material flow. The symbol F is an abbreviation of the name.
Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, that reacts with practically all organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. Elemental fluorine is highly toxic. Fortunately, the free element has a characteristic pungent odor, detectable in concentrations as low as 20 parts per billion, well below the safe working level.
Fluorine occurs chiefly in fluorspar (CaF2), apatite [Ca5(F,Cl,OH)(PO4)3] and cryolite (Na3AlF6), but it is rather widely distributed in other minerals. Modern commercial production methods are essentially variations on the procedures first used by Moissan.
Until World War II, there was no commercial production of elemental fluorine. The atom bomb project and nuclear energy applications, however, made it necessary to produce large quantities. Safe handling techniques have since been developed and it is now possible to transport liquid fluorine by the ton.
Fluorine and its compounds are used in purifying uranium (from the hexafluoride) and more than 100 commercial fluoro-chemicals, including many well known high-temperature plastics such as TeflonTM and TefzelTM. Hydrofluoric acid is extensively used for etching the glass of light bulbs and other objects.
Chlorofluorocarbons, commonly known as CFC's or by their trademark name, FreonsTM, were first prepared by Swarts and further developed by Midgley and Henne. They are extensively used in air conditioning and refrigeration. However, there is presently considerable concern over the environmental effects of such compounds, particularly on the ozone layer above the earth.
After many years of believing that the rare gases were chemically inert, it was discovered in the 1960's that fluorine compounds of these elements-such as XeF2 and XeF4-could be prepared readily. Fluorides of xenon, radon, and krypton have now been prepared.
Although fluoride ion in high concentrations is toxic, the addition of one part per million of fluorides (e.g., NaF) to public water supplies has reduced the incidence of dental caries, tooth decay, in many communities.