Xenon

Category: noble gas Atomic number: 54 Colour: colourless Melting point: −112°C (−169°F) Boiling point: −108°C (−163°F) First identified: 1898

For Sir William Ramsay and his colleague Morris Travers, 1898 was a remarkable year. It saw them, having discovered argon four years earlier, identifying both krypton and neon through their continued experiments with air. But they weren’t done yet – the industrial chemist Ludwig Mond gave them a liquid air machine, and they continued experimenting. On 12 July, they were using a vacuum vessel to remove some residues of argon and krypton when they noticed a small bubble of gas remaining behind. They treated this with potassium hydroxide to remove any carbon dioxide and ended up with a tiny sample in a vacuum tube – this gave off a beautiful blue glow when heated, and rendered a spectroscope reading quite different to krypton. The two men concluded they had found a new element and (once it became apparent that all the words meaning ‘blue’ had already been used) named it xenon, after the Greek word for ‘stranger’.

Xenon is a heavy gas. It is fascinating, for instance, to see how rapidly a balloon filled with it falls to the floor. (This needs to be done with care though, as it is an expensive gas to produce.) For a long time it was believed that xenon was completely inactive, until the British chemist Neil Bartlett and his team, working in Canada, came up with a brilliant experiment that showed it could form a compound with fluorine and platinum. Subsequently, more compounds have been found – it will react in the right conditions with gold, hydrogen and sulphur. However, the compounds are all unstable, as they tend to oxidize easily.

As a result, the main uses of xenon are currently based on the pure element. It is used in car headlamps to provide instant illumination, in high-speed electronic flash bulbs for photography, and in some kinds of lasers and sunbeds. It can theoretically be used as an effective anaesthetic, like a kind of laughing gas, but currently this would prove too expensive to be viable. Finally, Xenon Ion Propulsion Systems (XIPS) may sound like something from a science-fiction novel, but the term refers to a real piece of technology that is employed to manoeuvre satellites. The system ionizes xenon atoms and accelerates them to a speed of about 20 miles per second before ejecting them, propelling the satellite through space.