/ahr"gon/, n. Chem.
a colorless, odorless, chemically inactive, monatomic, gaseous element that, because of its inertness, is used for filling fluorescent and incandescent lamps and vacuum tubes. Symbol: Ar; at. no.: 18; at. wt.: 39.948.
[1890-95; < Gk, neut. of argós inactive, not working, idle, contr. of aergós equiv. to a- A-6 + érg(on) work + -os adj. suffix]

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Chemical element, chemical symbol Ar, atomic number 18.

Colourless, odourless, and tasteless, it is the most abundant of the noble gases on Earth and the one most used in industry. It constitutes about 1% of air and is obtained by distillation of liquid air. Argon provides an inert gas shield in welding and brazing, in lightbulbs and lasers, in Geiger counters, and in the production and fabrication of certain metals. Because a radioactive form of argon is produced by decay of a naturally occurring radioactive potassium isotope, it can be used to date rocks and samples more than 100,000 years old.

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  chemical element, inert gas of Group 18 (noble gases (noble gas)) of the periodic table (periodic law), terrestrially the most abundant and industrially the most frequently used of the noble gases. Colourless, odourless, and tasteless, argon gas was isolated (1894) from air by the British scientists Lord Rayleigh (Rayleigh, John William Strutt, 3rd Baron) and Sir William Ramsay (Ramsay, Sir William). Henry Cavendish (Cavendish, Henry), while investigating atmospheric nitrogen (“phlogisticated air”), had concluded in 1785 that not more than 1/120 part of air might be some inert constituent. His work was forgotten until Lord Rayleigh, more than a century later, found that nitrogen prepared by removing oxygen from air is always about 0.5 percent more dense than nitrogen derived from chemical sources such as ammonia. The heavier gas remaining after both oxygen and nitrogen had been removed from air was the first of the noble gases to be discovered on Earth and was named after the Greek word argos, “lazy,” because of its chemical inertness. ( helium had been spectroscopically detected in the Sun in 1868.)

      In cosmic abundance, argon ranks approximately 12th among the chemical elements. Argon constitutes 1.288 percent of the atmosphere by weight and 0.934 percent by volume and is found occluded in rocks. Although the stable isotopes (isotope) argon-36 and argon-38 make up all but a trace of this element in the universe, the third stable isotope, argon-40, makes up 99.60 percent of the argon found on Earth. (Argon-36 and argon-38 make up 0.34 and 0.06 percent of Earth's argon, respectively.) A major portion of terrestrial argon has been produced, since the Earth's formation, in potassium-containing minerals by decay of the rare, naturally radioactive isotope potassium-40. The gas slowly leaks into the atmosphere from the rocks in which it is still being formed. The production of argon-40 from potassium-40 decay is utilized as a means of determining Earth's age ( potassium-argon dating).

      Argon is isolated on a large scale by the fractional distillation of liquid air. It is used in gas-filled electric light bulbs, radio tubes, and Geiger counters (Geiger counter). It also is widely utilized as an inert atmosphere for arc-welding metals, such as aluminum and stainless steel; for the production and fabrication of metals, such as titanium, zirconium, and uranium; and for growing crystals of semiconductors (semiconductor), such as silicon and germanium.

      Argon gas condenses to a colourless liquid at −185.8° C (−302.4° F) and to a crystalline solid at −189.4° C (−308.9° F). The gas cannot be liquefied (thermal fusion) by pressure above a temperature of −122.3° C (−188.1° F), and at this point a pressure of at least 48 atmospheres is required to make it liquefy. At 12° C (53.6° F), 3.94 volumes of argon gas dissolve in 100 volumes of water. An electric discharge through argon at low pressure appears pale red and at high pressure, steely blue.

      The outermost (valence) shell of argon has eight electrons (electron), making it exceedingly stable and, thus, chemically inert. Argon atoms (atom) do not combine with one another; nor have they been observed to combine chemically with atoms of any other element. Argon atoms have been trapped mechanically in cagelike cavities among molecules (molecule) of other substances, as in crystals of ice or the organic compound hydroquinone (called argon clathrates).

atomic number
atomic weight
melting point
−189.2° C (−308.6° F)
boiling point
−185.7° C (−302.3° F)
density (1 atm, 0° C)
1.784 g/litre
oxidation state
electronic config.

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Universalium. 2010.

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