F; at. wt. 18.998403; at. no. 9; valence 1; elemental state F2. A halogen. Occurrence in earth's crust 0.065% by wt. Natural abundance of isotopes: 19F 100%; 18F (T 109.7 min) is prepared in nuclear reactors. Does not occur in elemental state in nature. Most important sources are fluorite, cryolite and florapatite, q.v.: Finger, "Fluorine Resources and Fluorine Utilization" in Advances in Fluorine Chemistry vol. 2, M. Stacey et al., Eds. (Butterworths, London, 1961) pp 35-54. Discovered in 1771 by Scheele. Isolated in 1886 by electrolysing a soln of potassium fluoride in anhydr hydrogen fluoride at - 23, using platinum-iridium electrode: Moissan, Compt. Rend. 102, 1543 (1886); 103, 202, 256. Subsequent methods of prepn: Ruff, Ber. 69, 181 (1936): Henne, J. Am. Chem. Soc. 60, 96 (1938). 18F has been used to study fluorine exchange reactions: Dave, Sowerby, "Isotopic Halogen Exchange Reactions" in Halogen Chemistry, vol. 1, V. Gutmann, Ed. (Academic Press, New York, 1967) pp 41-132. Reviews: A.J. Rudge, The Manufacture and Use of Fluorine and its Compounds (Oxford Univerity Press, 1962); O'Donnell, "Fluorine" in Comprehensive Inorganic Chemistry, vol. 2, J.C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 1009-1106; A.J. Woytek in Kirk-Othmer Encyclopedia of Chemical Technology vol. 10 (wiley-Interscience, New York, 3rd ed., 1980) pp 630-654.

Pale Yellow, diatomic gas, mp -219.61 (53.54K); bp -188.13 (85.02K); d (liq, -188.13) 1.5127; vapor pressure date: Hu et al., J. Am. Chem. Soc. 75, 5642 (1953); White et al., ibid 76, 2584 (1954). Crit. temp: -129; crit. pressure: 55 atm. Most reactive nonmetal; higher oxidation potential than ozone; most electronegative element; E (calc) F/F -2.9V. F-F bond weaker than Cl-Cl and Br-Br bonds; enthalpy of dissociation: 37.7 kcal. Reacts vigorously with most oxidizable substances at room temp, frequently with ignition. Combines directly or indirectly, to form fluorides with all the elements except helium, neon and argon. Dec water, giving hydrofluoric acid, HF, oxygen fluoride, OF2, hydrogen peroxide, oxygen and ozone. Reacts with nitric acid, forming the explosive gas, fluorine nitrate, NO3F; with sulfuric acid, giving fluorosulfuric acid, HFSO3. Yields the metal fluorides, water, oxygen and oxygen fluoride when made to react with metal hydroxides in the cold. Reacts violently with organic compds, usually with disintegration of the molecule. Under controlled conditions, however, hydrocarbon vapors may be fluorinated with elemental fluorine. Solid fluorine explodes when brought in contact with liquid hydrogen. Under ordinary conditions it does not react directly with oxygen, nor does it react with oxides of sodium, potassium or calcium. LC50 (1 hr) inhalation by rats, mice, guinea pigs: 185, 150, 170 ppm (by vol). Keplinger, Suissa, Am. Ind. Hyg. Assoc. J. 29, 10 (1968).

Caution: Dangerous to inhale. Strong caustic action on eyes, skin, mucous membranes. Chronic absorption can cause mottled enamel of teeth, osteosclerosis and calcification of ligaments.
Ref.: 4090, 651 pp.
The Merck Index - Eleventh Edition.
Copyright 1989 by Merck & Co., Inc.