Fluorine "F" is the chemical element with atomic number 9. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic molecules, F2. Fluorine is the most electronegative element and is extremely reactive, requiring great care in handling. It has a single stable isotope, fluorine-19.
In stars, fluorine is rare compared to other light elements. In Earth's crust, fluorine is the thirteenth most abundant element. Fluorine's most important mineral, fluorite, was first formally described in 1530, in the context of smelting. The mineral's name derives from the Latin verb " fluo", which means "flow", because fluorite was added to metal ores to lower their melting points. Suggested as a chemical element in 1811, fluorine was named after the source mineral, but resisted many attempts to isolate the element. In 1886, French chemist Henri Moissan succeeded. His method of electrolysis remains the industrial production method for fluorine gas. The main use of elemental fluorine, uranium enrichment, was developed during the Manhattan Project.
Because of the difficulty in making elemental fluorine, most fluorine used in commerce is never converted to free fluorine. Instead, hydrofluoric acid is the key intermediate for the $16 billion per year global fluorite-chemical industry. The fluorides of low charged metals are ionic compounds (salts); those of high charged metals are volatile molecular compounds. The largest uses of inorganic fluorides are steel making and aluminium refining.
Organic fluorine compounds tend to have high chemical and thermal stability. The largest commercial use is in refrigerant gases. Although traditional chlorofluorocarbons (CFCs) are widely banned, the replacement gases still contain fluorine. Polytetrafluoroethylene (Teflon) is the most important fluoropolymer and is used in electrical insulation, chemical-resistant parts, stadium roofs, and cookware. A growing fraction of modern pharmaceuticals contain fluorine; Lipitor and Prozac are prominent examples. While a few plants and bacteria synthesize organofluorine poisons, fluorine has no metabolic role in mammals. The fluoride ion, when directly applied to teeth, reduces decay and for this reason is used in toothpaste and municipal water fluoridation.
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