FLUORINE (F/9)

* Fluorine is a member of the halogen family:

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   FLUORINE / F / 9

   Fluorine is normally found as diatomic F2 gas, which has a pale
   greenish-yellow color.  Only one isotope is found in nature,
   F<19/9>, which is stable.

     atomic weight:       18.9984032
     abundance:           13th
     density:             1.7 gm/l
     melting point:       -220 C
     boiling point:       -188 C
     valence:             1
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The "F-" ion is known as "fluoride". Fluorine is mostly derived from the mineral fluorspar and has significant uses in industry, with production in the millions of tonnes a year. Hydrofluoric acid is useful because it is one of the most potent and corrosive of all acids, even capable of attacking glass, which makes it useful for glass etching. Fluorine compounds are used as plastics and refrigerants.

Fluorine is combined with uranium to form uranium hexafluoride gas (UF6) for isotopic separation or "fuel enrichment". Traces of sodium fluoride (NaF) are also added to reservoirs to reduce tooth decay; however, high concentrations are toxic, and there is a long-standing fringe movement opposed to the fluoridation of water supplies.