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  • An element that is a member of the 8A group (Noble Gases) of the periodic table. Argon is represented by the atomic symbol Ar, has an atomic number of 18, and an atomic weight of 39.948. It is colorless, odorless, and a very inert gas. It comprises about 1% of the Earth's atmosphere. [Chemical & Engineering News; v73n36; 8; 1995.] [Chemistry The Central Science; Brown, Theodore; Lemay, H. Eugene; Bursten, Bruce; p. 846; 1994; Prentice Hall; Englewood Cliffs, New Jersey.] Source: Atmospheric Chemistry Glossary


Atomic Number: 18
Atomic Symbol: Ar
Atomic Weight: 39.948
Electron Configuration: [Ne]3s23p6

History
(Gr. argos, inactive) Its presence in air was suspected by Cavendish in 1785, discovered by Lord Rayleigh 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 ppm 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.

Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.