[53] In contrast to gold's distinctly ionic trifluoride, its trichloride and tribromide are volatile dimeric molecules. [35] HF's weakness as an aqueous acid is paradoxical considering how polar the HF bond is, much more so than the bond in HCl, HBr, or HI. The name later evolved into fluorspar (still commonly used) and then fluorite. [178], Fluorite mining, which supplies most global fluorine, peaked in 1989 when 5.6 million metric tons of ore were extracted. Thus if little energy was added (low temperatures), then the compound could exist; however, the synthesis is a serious problem (not yet solved). [9] This is a result of the relatively large electron and internuclear repulsions, combined with a relatively small overlap of bonding orbitals arising due to the small size of the atoms. It combines with metals, nonmetals, metalloids, and most noble gases,[96] and almost exclusively assumes an oxidation state of −1. Lower-period elements, however, may form hypervalent molecules, such as phosphorus pentafluoride or sulfur hexafluoride. [114] "Solid fluorine carriers", compounds that can release fluorine upon heating, notably cobalt trifluoride,[115] may be used instead, or hydrogen fluoride. Natural organofluorines have been found in microorganisms and plants[66] but not animals. [86][88] In 1886, after 74 years of effort by many chemists, Moissan isolated elemental fluorine. [228][229] Quinolones are artificial broad-spectrum antibiotics that are often fluorinated to enhance their effects. [63], As with other iron alloys, around 3 kg (6.5 lb) metspar is added to each metric ton of steel; the fluoride ions lower its melting point and viscosity. [191] Other important inorganic fluorides include those of cobalt, nickel, and ammonium. First synthesized in the late 19th century, it was recognized as an insecticide in the early 20th, and was later deployed in its current use. The transition from β- to α-fluorine is more exothermic than the condensation of fluorine, and can be violent. [123] Metal fluorides with more fluorine atoms are particularly reactive. [6], The fluorine–fluorine bond of the difluorine molecule is relatively weak when compared to the bonds of heavier dihalogen molecules. [8] The covalent radius of fluorine of about 71 picometers found in F2 molecules is significantly larger than that in other compounds because of this weak bonding between the two fluorine atoms. [213] Other examples include terminally fluorinated fatty acids, fluoroacetone, and 2-fluorocitrate. [113], The carbon–fluorine bond of the smaller molecules is formed in three principal ways: Fluorine replaces a halogen or hydrogen, or adds across a multiple bond. Of the neutral +7 species, only iodine heptafluoride is known. This burgeoning nuclear industry later drove post-war fluorochemical development. [63][79][183], At least 17,000 metric tons of fluorine are produced each year. [222] Sodium monofluorophosphate and sometimes sodium or tin(II) fluoride are often found in fluoride toothpastes, first introduced in the U.S. in 1955 and now ubiquitous in developed countries, alongside fluoridated mouthwashes, gels, foams, and varnishes.[222][223][relevant? Global fluorochemical sales amount to more than US$15 billion a year. [163] Polytetrafluoroethylene (PTFE), the simplest fluoropolymer and perfluoro analogue of polyethylene with structural unit –CF2–, demonstrates this change as expected, but its very high melting point makes it difficult to mold. VDF/HFP is a copolymer system of vinylidene fluoride and (at least 20%) hexafluoropropylene. [88] Oxygen's highest fluoride is oxygen difluoride,[88] but fluorine can theoretically (as of 2012) oxidize it to a uniquely high oxidation state of +4 in the fluorocation: OF+3. The latter are stabilized by more fluorine atoms and lighter central atoms, so sulfur hexafluoride is especially inert. [174] Frequent passivation, along with the strict exclusion of water and greases, must be undertaken. Fluorine (F 2), composed of two fluorine atoms, combines with all other elements except helium and neon to form ionic or covalent fluorides. [116] In contrast, the fluoropolymers are formed by polymerizing free radicals; other techniques used for hydrocarbon polymers do not work in that way with fluorine.
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