Fluorine F

Discovery

The mineral fluorite (calcium fluoride) was used as a flux in metal smelting as early as the sixteenth century; Georgius Agricola described it in 1529. In the 1770s Carl Wilhelm Scheele treated fluorite with acid and produced hydrofluoric acid, which etches glass. By the early nineteenth century chemists, including André-Marie Ampère and Humphry Davy, suspected the acid contained an unknown element similar to chlorine.

Isolating it proved extraordinarily difficult and dangerous. The element attacked every container, and hydrogen fluoride vapour injured several experimenters; some are reported to have died from the exposure. Success finally came on 26 June 1886, when the French chemist Henri Moissan electrolysed a solution of potassium hydrogen fluoride in liquid hydrogen fluoride at low temperature, using platinum–iridium apparatus. He collected a gas at the anode that set silicon on fire, and received the Nobel Prize in Chemistry in 1906.

Origin of the name

The name derives from fluorite, whose own name comes from the Latin fluere, 'to flow', because the mineral helps ores melt and flow in a furnace. The same mineral gave its name to fluorescence, since some samples glow under ultraviolet light. The symbol is F.

Main uses

• Dental health: fluoride in toothpaste, and in drinking water in some countries, strengthens tooth enamel against decay.
• Polymers: PTFE (Teflon), discovered by accident in 1938, gives non-stick cookware and chemically resistant seals.
• Nuclear fuel: uranium hexafluoride is the gas used to enrich uranium.
• Pharmaceuticals and agrochemicals: adding fluorine atoms can make drugs more stable in the body; many widely used medicines contain fluorine.
• Cooling and electronics: fluorinated refrigerants, etching gases for semiconductor manufacturing, and lithium hexafluorophosphate in lithium-ion battery electrolytes.

Isotopes

Fluorine has only one stable isotope, fluorine-19. The most important radioactive isotope is fluorine-18, with a half-life of about 110 minutes. Attached to a sugar molecule it forms FDG, the most widely used tracer in PET scanning, which highlights tissues that consume a lot of glucose, such as many tumours. Its short half-life means it must be produced in a cyclotron close to the hospital.

In everyday life

Fluoride at the low levels found in toothpaste is safe and beneficial, but swallowing large amounts is harmful, and long-term excessive intake during childhood can cause dental fluorosis, faint white marks on the teeth. Elemental fluorine gas and hydrofluoric acid are extremely hazardous; the acid can penetrate skin and damage deeper tissue.

Chlorofluorocarbons (CFCs), once common in refrigerators and aerosols, damaged the ozone layer and were phased out under the 1987 Montreal Protocol.