Fluorine

For centuries, a mineral called fluorspar (calcium difluoride) was added to metal ores to lower their melting points for smelting in metal refining. "Fluor" comes from the Latin word fluere, meaning "to flow." A solution containing fluorite and sulfuric acid was later discovered to produce a substance (hydrofluoric acid) that could be used in glass etching. The component of these compounds that would be come to be known as fluorine was proposed as an element in 1810. Fluorine is so reactive, however, that it does not occur freely in nature, and the element proved difficult and dangerous to isolate.

Many investigators tried to separate fluorine from hydrofluoric acid, with some experiments ending tragically. Most chemists studying fluorine in the 1800s were poisoned by their research—except for George Gore. He was never poisoned by his research, but he didn’t survive his research unscathed. Gore was able to isolate a small amount of the volatile element through an electrolytic process in 1869. However, when the fluorine gas that formed on one of his electrodes reacted with the hydrogen gas that formed on the other, he discovered the hard way that fluorine and hydrogen gas combine explosively, destroying most of his lab and nearly poisoning him, but he managed to escape unharmed.

Following 74 years of continuous effort by various scientists, chemist Ferdinand Frederic Henri Moissan finally isolated fluorine in 1886 (after being poisoned several times in his pursuit) through the electrolysis of potassium fluoride and hydrofluoric acid. He completely isolated the fluorine gas from the hydrogen gas and built his electrolysis device from pure platinum. Moissan was awarded the Nobel Prize for chemistry in 1906 for his work with fluorine, and in fact, his design has never been outdone and is still used in fluorine production.

Fluorine is a pale yellow, corrosive gas and the absolute worst at sharing. It’s the most electronegative element, meaning that when it bonds with other atoms, fluorine pulls all of the electrons towards itself. Fluorine is also the most reactive element. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame.

Until World War II, there was no commercial production of elemental fluorine. The Manhattan Project and nuclear energy applications, however, made it necessary to produce large quantities of the gas.

Fluorine is now used in producing uranium (from the hexafluoride) and more than 100 commercial fluorochemicals, including high-temperature plastics. Fluorine-carbon compounds, known as chlorofluorocarbons (CFCs), were once used extensively in aerosols and refrigerants but have been phased out because of their negative impact on the environment.

Fluorine is also used in city water treatment (at one part per million) and in toothpaste to prevent tooth decay. Hydrofluoric acid is used to etch glass, including that of light bulbs. Fluorspar (calcium fluoride) crystals are used to make infrared lenses.

Noteworthy compounds include sodium fluoride, stannous(II) fluoride, and sodium monofluorophosphate, which are common toothpaste additives. Chemical reactions between fluorine and noble (virtually inert) gases have been confirmed in fluorides of xenon, radon, and krypton.

Fluorine is isolated through electrolysis of potassium fluoride and hydrofluoric acid as well as through the electrolysis of molten potassium acid fluoride.