A

Argon

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MELTING POINT: −189.3°C
BOILING POINT: −185.8°C
DENSITY: Unknown
MOST COMMON IONS: None known

Argon is an odorless, colorless monatomic gas at room temperature. Although it constitutes about 1 percent of the atmosphere, it was not discovered until 1894, when John William Strutt (Lord Rayleigh) and William Ramsay isolated it from the more reactive components of air. Argon is the most abundant noble gas and it was the first to be found. Its discovery prompted confusion over how to fit it into the periodic table: No other inert, monatomic gases were then known. Furthermore, its atomic weight placed it between the very reactive metals potassium and calcium. Ramsay suggested a new family of elements (the noble gases), and had isolated four additional members by 1898.

The element takes its name from the Greek argos, meaning slow or lazy, because it is extremely unreactive. Indeed, its first stable neutral compound, argon fluorohydride (HArF), was not reported until 2000, and it exists only within a low-temperature solid matrix. Because argon in effect does not form chemical bonds, it is frequently used in the research of nonbonding chemical interactions, such as van der Waals forces and surface adsorption. Inertness makes argon useful in incandescent light bulbs: It protects the hot filament from oxidation and slows its evaporation. It is used to generate an inert atmosphere for other chemical reactions in industry and research. Argon is the glowing gas that occupies some fluorescent tubes, and it is an insulating filler in some double-pane thermal windows.

The principal isotope of argon is ⁴⁰Ar (99.6% abundance); it has two other stable isotopes, ³⁶Ar (0.3%) and ³⁸Ar (0.1%). Argon-40 is formed by β-decay of the long-lived potassium isotope ³⁹K.

SEE ALSO NOBLE GASES; RAMSAY, WILLIAM; STRUTT, JOHN.

Carmen Giunta

Bibliography

Emsley, John (1998). The Elements, 3rd edition. Oxford, U.K.: Clarendon Press.

Emsley, John (2001). Nature's Building Blocks: An A–Z Guide to the Elements. New York: Oxford University Press.

Internet Resources

WebElements™ Periodic Table Available from <http://www.webelements.com/>.