With a name taken from the Greek helios for "sun", helium is the second lightest and second most abundant gas in the known universe (hydrogen being number one). Because of its scarcity in our atmosphere its existence was not suspected until spectroscopic measurements revealed an unknown element present in the sun. The discovery of helium is generally credited to Janssen and Lockyear in 1868.
As no helium compounds are known, this family of gases was once thought to be inert. In 1962 the first noble gas compound was prepared with xenon (see below). Still, helium only occurs in uncombined form and must either be extracted from the atmosphere by liquefaction of air or separated from deposits of natural gas. It is thought that some of the terrestrial helium is the product of the alpha decay of radioactive isotopes beneath the crust.
Helium is the only known element which cannot be converted to a solid simply by cooling. It has 98% the lifting power of hydrogen with none of the Hindenburg-type drawbacks, and is still used today in airships.
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The fourth most abundant element in the known universe, neon was discovered in 1898 by Ramsay and Travers. Its name is taken from the Greek neos or "new".
This is perhaps the best known noble gas because of its use in so-called "neon" lights (many of which actually contain other gases) and is relatively plentiful in the earth's atmosphere (fifth in abundance, following carbon dioxide). No stable compounds of neon are known to date. The gas is extracted from air by liquefaction.
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Argon is third in abundance in the earth's atmosphere (about 1% by volume). Rayleigh and Ramsay isolated and identified the gas in 1894. Like the rest of the noble gases, it is colorless, tasteless and odorless. The name for argon is taken from the Greek argos for "inactive".
For years argon has been used in ordinary incandescent light bulbs to replace the oxygen that would otherwise shorten the lifetime of the filament. It is used in some types of welding where active atmospheric gases would interfere with the process. Argon is also used in various types of "black lights" or UV lamps since excitation of the gas produces a significant amount of ultraviolet radiation. A few curious compounds have been made with argon but they are not very stable.
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Named from the Greek kryptos or "hidden", krypton is neither green nor a solid material that can defeat Superman. Rather it is another noble gas discovered in 1898 by Ramsay and Travers. It ranks sixth in abundance in the atmosphere. Krypton gas is used in various kinds of lights, from small bright flashlight bulbs to special strobe lights for airport runways.
As with the other noble gases, krypton is isolated from the air by liquefaction.
One of the naturally occurring non-radioactive isotopes of krypton, Kr-86 (17.3%) is used as the basis for the current international definition of the meter. One meter is 1,650,762.73 wavelengths of the red-orange spectral line of krypton-86.
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Also discovered by Ramsay and Travers in 1898, xenon (from the Greek xenos for "strange") is the rarest of the stable noble gases in the air. It is still recovered by liquefaction techniques and is widely used in strobe lamps.
In 1962 the first noble gas compound was produced by Neil Bartlett, combining xenon, platinum and fluorine. It is now possible to produce xenon compounds in which the oxidation states range from +2 to +8(!).
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Discovered in 1900 by Friedrich Dorn, radon is a radioactive noble gas now regarded as a potential health hazard in some homes. It also has medical applications for cancer treatment. Its original name was to be niton for "shining" but it was eventually named as a derivative of radium. Radon is found in underground deposits where is it produced by uranium and radium decay.
Radon fluoride (RnF) has been produced and the element glows with a yellow light in the solid state.
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