inert gas

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inert gas

or

noble gas,

any of the elements in Group 18 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
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. In order of increasing atomic number they are: heliumhelium
, gaseous chemical element; symbol He; at. no. 2; at. wt. 4.0026; m.p. below −272°C; at 26 atmospheres pressure; b.p. −268.934°C; at 1 atmosphere pressure; density 0.1785 grams per liter at STP; valence usually 0.
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, neonneon
[Gr.,=new], gaseous chemical element; symbol Ne; at. no. 10; at. wt. 20.1797; m.p. −248.67°C;; b.p. −246.048°C;; density 0.8999 grams per liter at STP; valence 0. Neon is a colorless, odorless, and tasteless gas.
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, argonargon
[Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0. Argon is a colorless, odorless, tasteless gas occurring in air (of which it constitutes 0.
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, kryptonkrypton
[Gr.,=hidden], gaseous chemical element; symbol Kr; at. no. 36; at. wt. 83.798; m.p. −156.6°C;; b.p. −152.3°C;; density 3.73 grams per liter at STP; valence usually 0. Krypton is a colorless, odorless, tasteless gas.
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, xenonxenon
[Gr.,=strange], gaseous chemical element; symbol Xe; at. no. 54; at. wt. 131.293; m.p. −111.9°C;; b.p. −107.1°C;; density 5.86 grams per liter at STP; valence usually 0. Xenon is a rare, colorless, odorless, tasteless, chemically unreactive gas.
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, and radonradon
, gaseous radioactive chemical element; symbol Rn; at. no. 86; mass no. of most stable isotope 222; m.p. about −71°C;; b.p. −61.8°C;; density 9.73 grams per liter at STP; valence usually 0. Radon is colorless and the most dense gas known.
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. They are colorless, odorless, tasteless gases and were once believed to be entirely inert, i.e., forming no chemical compounds; however, some compounds of these elements have been produced, i.e., fluorides of krypton, xenon, and radon. The low chemical activity of the inert gases is due to the fact that their outermost, or valence, electron shell is complete, containing two electrons in the case of helium and eight in the remaining cases. The inert gases are sometimes called the rare gases, although argon is not rare (it makes up about 1% of the atmosphere) and helium is commercially extracted from natural gas and the atmosphere.

Bibliography

See G. A. Cook, Argon, Helium and the Rare Gases (2 vol., 1961); I. Asimov, The Noble Gases (1966).

inert gas

[i′nərt ′gas]
(chemistry)