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fluorine (F)

A pale yellow, highly corrosive, highly poisonous, gaseous element. It occurs naturally as fluorite, cryolite, and fluorapatite (see apatite). Fluorine is the lightest halogen and the most electronegative, oxidizing, and reactive of all the elements. Steel wool bursts into flames when exposed to it. Most nonmetal fluorides are highly reactive, but sulfur hexafluoride (used as an electrical insulator) and carbon tetrafluoride are inert.

Fluorine is used in a wide variety of industrially important compounds. It was discovered in 1529, but first isolated by Henri Mossian (1852–1907) in Paris in 1866. He added potassium hydrogen fluoride to liquid hydrogen fluoride and then passed an electric current through the solution. By carrying out the electrolysis in a U-tube made of platinum-indium alloy with electrodes of the same material, Mossian obtained fluorine gas. The fluoride solution has a very electrical resistance and a heavy current is needed to bring about electrolysis. The passage of this currents heats up the apparatus, so the cell has to be cooled.

Fluorine salts, known as fluorides, were used for centuries in welding metals and for frosting glass before the element itself was isolated. Fluorine is used in a wide variety of industrially important compounds. It is also used to make uranium hexafluoride, needed by the nuclear power industry, and sulfur hexafluoride insulating gas for high-power electricity transformers, and to treat polythene to make it impermeable to solvents.

atomic number 9
atomic mass 18.998
electron configuration 1s22s22p5
first ionization energy 1,681 kJ/mol
electronegativity 4.0
atomic radius 71 pm
ionic radius 136 pm
melting point -219.62°C (-363.32°F)
boiling point -188.14°C (-307.45°F)
relative density 1.108

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