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April 18, 2012

Fluorine could be a troubled and misunderstood teenager or an unsavoury desperate character hell-bent on getting one extra electron to complete its outer shell. This angry and avaricious element will seemingly go to any lengths to get its fix by stealing electrons from any other element in the periodic table. Only two elements, helium and neon, have managed to resist fluorine’s brutal methods of persuasion. Like a true miser nothing can convince fluorine to part with its own electrons. Perhaps its all down to a difficult childhood. It took 74 years of blood, sweat and tears between Andre-Marie Ampere proposing the existence of fluorine and its isolation by Henri Moissan. Its not easy to trap a gas that eats through most containers. Early attempts to isolate the element resulted in the blinding and death of several scientists (now known as the “Fluorine Martyrs”).

Fluorine the element is a noxious pale yellow gas that is rarely used in its pure form however its main use is in uranium enrichment for nuclear reactors – a process developed during the Manhattan Project. Another notorious application is in the compounds chlorofluorocarbons (CFCs) developed by Thomas Midgley (perhaps the most polluting individual to have ever lived). CFC compounds are now largely banned but not before inflicting major damage on the Earth’s protective ozone layer. It is not then very surprising that fluorine has a bad reputation and when it tries to do good people suspect an ulterior motive.

Fluorine must be the source of more conspiracy theories than any other element. Despite having no known biological function fluoride is sometimes added to drinking water for health reasons (fluorine refers to the element F, flouride means an atom of fluorine with a stolen electron F-). Fluoride has been proved to protect teeth from decay. It works by reacting with the enamel in teeth to form a hard mineral called fluorapatite which prevents cavities forming. The flouride has to come in contact with the teeth so the most effective treatment is to brush with fluoridated toothpaste but many countries still add fluoride to drinking water as it still shows an improvement in health. Consequently adding fluoride to drinking water is the cheapest most effective health care programme any government can instigate but you can see why people get paranoid.

A more exotic use of fluorine is as rocket fuel in place of oxygen. Apparently both the Americans and Russians conducted research into fluorine fuel but later abandoned it for reasons that will become obvious. On paper fluorine is a brilliant choice, being very electron greedy makes it very reactive, being reactive means a lot of energy is released very quickly – just the job if you want to launch a rocket.

A molecular model of Teflon

On the down side fluorine is not the nicest element to work with (see earlier comments on the Fluorine Martyrs). Another problem is the product of a reaction between hydrogen (the other component of the rocket fuel) and fluorine – hydrogen fluoride (HF). HF is a mild acid but with a devious nature. It is absorbed rapidly through skin and eyes and reacts with pretty much everything in its path down to the bone. The fluoride causes nerve damage meaning people often don’t notice they have been burned and making early treatment less common. When HF gets in to the blood it reacts with calcium ions to form insoluble calcium flouride – having lumpy bits in your blood is a bad thing.

But its not all scaremongering and amputations, fluorine compounds can be very stable and very safe. Fluorine containing compounds have given us good things – non-stick pans and extra slippery skis in the form of Teflon, fire retardants and anaesthetics in the form of hydrofluorocarbons and fluorocarbons, but the one that will entertain a chemist for longest is sulphur hexafluoride (SF6). SF6 is a colourless and inert gas that is heavier than air. Balloons of SF6 will sink like a stone and if you inhale the gas it changes your voice to a bass-baritone (the opposite effects to inhaling helium). You can also fill a fish tank with it and float paper boats on what looks like nothing (more fun than it may sound, especially for a nerd). Perhaps I should get out more.

Next time a periodic tale is off to see the bright lights in a big city – its neon!


Images by @SciCommStudios

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