![]() ![]() The argon does the stirring while the oxygen removes carbon as carbon dioxide. Most argon is used in the production of steel where it is blown through the molten iron, along with oxygen. Cavendish did not realise that he had stumbled on a new gaseous element. He passed electric sparks through air and absorbed the gases which formed, but he was puzzled that there remained an unreactive 1 per cent. In fact, argon had been isolated earlier in 1785 in Clapham, South London, by Henry Cavendish. The atomic spectrum of this '1 per cent' showed new red and green lines, confirming that it was a new element. He was left with 1 per cent which would not react and which was denser than nitrogen (1.784 g dm -3). Ramsay removed all the nitrogen from his sample by repeatedly passing it over heated magnesium to form magnesium nitride. ![]() Ramsay wrote to Rayleigh suggesting that he would look for a heavier gas in the nitrogen obtained from air, while Rayleigh should look for a lighter gas from ammonia. The story of its discovery began when Rayleigh found that the nitrogen extracted from the air had a higher density (1.257 g dm -3) than nitrogen made by decomposing ammonia (1.251 g dm -3). In 1904 Rayleigh won the Nobel prize in physics and Ramsay won the Nobel prize in chemistry for their work on the discovery of argon. Although argon makes up 0.93 per cent of the atmosphere, the gas evaded discovery until 1894 when the physicist Lord Rayleigh (1842-1919) and the chemist William Ramsay (1852-1916) identified it. Almost all of this Ar has come from the decay of the radioactive isotope potassium-40, which has a half-life of 12.7 billion years. There are 50 trillion tonnes of argon swirling around in the Earth's atmosphere, which has slowly built-up over billions of years. No other process has induced argon to react, including high temperatures, electrical discharges, or ionising radiation. On warming above -246☌ HArF reverted back to Ar and HF. Then in 2000, chemists at the University of Helsinki, led by Markku Räsänen, announced the first argon compound - argon fluorohydride (HArF) - which they made by condensing a mixture of argon and hydrogen fluoride onto caesium iodide at -265☌ and exposing it to uv light. Argon's name comes from the Greek word argos, meaning lazy and indeed for more than 100 years after its discovery chemists were unable to get it to combine with any other element. ![]()
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