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Argon

Author: Robert Husted, Mollie Boorman

Atomic Number 18
Atomic Symbol Ar
CAS ID No. 7440-37-1
Atomic Weight 39.9480 amu
Electron Configuration [Ne] 3s2 3p6
Melting Point -189.2 C
Boiling Point -186 C
Density 1.740 g/cm3
History

(Gr. argos, inactive) Its presence in air was suspected by Cavendish in 1785, discovered by Lord Raleigh and Sir William Ramsay in 1894.

Sources

The gas is prepared by fractionation of liquid air because the atmosphere contains 0.94% argon. The atmosphere of Mars contains 1.6% of  40Ar and 5 p.p.m. of  36Ar.

Properties

Argon is two and one half times as soluble in water as nitrogen, having about the same solubility as oxygen. Argon is colorless and odorless, both as a gas and liquid. Argon is considered to be a very inert gas and is not known to form true chemical compounds, as do krypton, xenon, and radon.

Isotopes

Naturally occurring argon is a mixture of three isotopes. Twelve other radioactive isotopes are known to exist.

Uses

It is used in electric light bulbs and in fluorescent tubes at a pressure of about 400 Pa. and in filling photo tubes, glow tubes, etc. Argon is also used as an inert gas shield for arc welding and cutting, as blanket for the production of titanium and other reactive elements, and as a protective atmosphere for growing silicon and germanium crystals.




Last Update: 2011-02-16