Fluorine
From Encyclopædia
Fluorine is a
Pale yellow, poisonous, highly corrosive gas. It is the lightest member of the HALOGENS, Group VIIA of the
periodic table, and the most reactive of all elements. Its symbol is F, its
atomic weight is 18.99840, and its
atomic number is 9. The name fluorine is derived from the mineral fluorspar, which, in turn, is derived from the Latin fluo ("flow"), because until AD 1500 it was used as a flux in
metallurgy.DISCOVERYBy 1670 the German scientist Heinrich Schwanhard had discovered that glass can be etched by fluorspar treated with a strong acid. This treatment generates hydrofluoric acid, HF, a highly corrosive acid still used for
etching glass. Although Carl S. Scheele of Sweden is often credited with the discovery of hydrofluoric acid, it seems apparent that he and most of his contemporaries believed that the acid is an integral part of the fluorspar, not realizing the significance of adding a strong acid when activating the mineral. The true nature of the acid did not begin to emerge until early in the 19th century. Unsuccessful attempts to separate and characterize the unknown element by the electrolysis of fluorspar were made by Edmond Fremy in France and George Gore in England, among others. Success came in 1886 when Henri Moissan, a student of Fremy, used a solution of
potassium acid fluoride, KHF(2), in anhydrous hydrofluoric acid as the electrolyte.NATURAL OCCURRENCEFluorine is relatively abundant in the universe. According to some theorists, this may be attributed to the formation of the element by
supernova explosions, when
neutrinos transform an isotope of neon into one of fluorine. On the Earth, fluorine is widely distributed among natural compounds, but its extreme reactivity precludes its presence in elemental form. Although constituting only 0.065 percent of the Earth's crust, fluorine is found in oceans, lakes, rivers, and all other forms of natural water; in the bones,
teeth, and blood of all
mammals; and in all
plants and
plant parts. In spite of its ubiquity, as yet no universally acceptable
evidence exists that fluorine is a necessary ingredient of living beings. Fluorine is found most abundantly in nature as the minerals fluorspar (FLUORITE),
cryolite, and fluorapatite. Fluorspar is found extensively in Illinois and Kentucky.
cryolite occurs extensively in Greenland and Iceland, although its use in the production of aluminum is so extensive that much of the supply needed for other manufacturing must be produced synthetically.PROPERTIESFluorine exists as a diatomic gas. Highly toxic, it has a characteristic pungent odor that can be detected before hazardous concentrations build up. Fluorine
boils at - 188 deg C (- 370 deg F) and its melting point is - 219 deg C (- 426 deg F).Only one stable isotope of fluorine occurs. The fluorine
atom has seven
electrons in its outer
shell and requires an additional
electron for maximum stability. This
electron is strongly attracted by the positively charged
nucleus because of the small size of the fluorine
atom,
accounting for the extreme electronegativity of the element. As a result, fluorine has a valence of -1 and forms compounds with all elements except the noble gases helium, neon, and argon. Fluorine salts are called fluorides.Fluorine is manufactured by electrolyzing a mixture of
potassium fluoride and hydrogen fluoride. It is stored and shipped in containers lined with TEFLON or made of a special steel. The latter becomes coated with
iron fluoride, thus retarding further reaction.THE FLUORINE INDUSTRYThe earliest large-scale commercial use of fluorine-containing compounds was probably the result of the work of General Motors Corporation chemists Thomas Midgley and Albert Henne, who, in the 1920s, set out to develop a refrigerant that did not have the drawbacks of those used at the time. The result was a chlorofluorocarbon, dichlorodifluoromethane, now called FREON-12. It is nonflammable, noncorrosive, and nontoxic; it liquefies easily and
boils at a low temperature (-29.8 deg C/-21.6 deg F). Joint production by General Motors and Du Pont began in 1931, and a whole family of these refrigerants was subsequently developed. The use of chlorofluorocarbons was rapidly expanded into the field of AEROSOL propellants. Their use declined after 1977, however, when it was found that they deplete the ozone in the upper
atmosphere, and several
nations have proposed banning their use as propellants and refrigerants by the end of the 20th century (see
OZONE LAYER).The fluorochemical industry actually began in the
United States about 1940, when the Du Pont Corporation developed a polymer of a tetrafluoroethylene, Teflon TFE. The introduction of this product resulted in a dramatic increase in fluorine requirements (See
plastics). Later demands arose for the element, for use in a gaseous diffusion process that concentrated
uranium isotopes for the manufacture of nuclear
weapons. This was done by the chemical
conversion of ore to gaseous
uranium hexafluoride, followed by the separation of stable
uranium-238 from fissionable
uranium-235 by gaseous diffusion. In addition to the resulting demand for fluorine, the corrosive nature of these products meant that fluorocarbon coolants had to be developed for removing the heat generated while pumping the
uranium hexafluorides.USES AND COMPOUNDSIn addition to its use in
uranium processing, refrigerants, and aerosol propellants, fluorine is used in dentifrices, as a catalyst in producing the dodecylbenzene used to make detergents, and in alkylating olefins used in refining high-octane gasoline, as we?l as in the production of polyfluorhydrocarbon
resins such as TEFLON, noted for their nonstick properties and resistance to corrosion.
sodium fluoride, NaF, is used as a sterilant insecticide and in FLUORIDATION OF WATER. It is also a paint preservative, it renders
enamels opaque, and it is used in dyes and in the primary
metal and ceramics industries. Boron trifluoride is a catalyst in the alkylation of benzene for detergent production and in making polymers and copolymers for adhesives.Other compounds include antimony trifluoride, an
organic chemistry catalyst;
sulfur hexafluoride, a gaseous insulator; and several polymers such as vinylidene fluoride. Fluorine compounds are of
interest whenever incombustibility or oil and water resistance are important. They are also used in elastomers and in surfactants for the preparation of coatings applied to fiberboard, paper, and cloth.Charles HowardBibliography: Filler, R., and Kobayashi, Y., eds., Biomedical Aspects of Fluorine Chemistry (1983); Liebman, Joel, and Greenberg, Arthur, eds., Fluorine-Containing
molecules (1989); O'Donnell, T. A., The Chemistry of Fluorine (1975); Young, A. S.,
sulfur Dioxide,
chlorine, Fluorine and
chlorine Oxides (1983).
