Nomenclature
CAS number: 7440-37-1
Description and references
Ar; at. wt 39.948; at. no. 18. Group VIIIA
(18), also known as Group 0. A noble gas characterized by an electronic
structure in which the outer p subshell is entirely filled:
1s22s22p63s23p6. Stable
naturally occurring isotopes (mass numbers): 36 (0.337%); 38 (0.063%);
40 (99.600%); known artificial radioactive isotopes: 32-35; 37; 39;
41-46. Longest-lived known isotope: 39 (T 269 years, β-emitter).
Abundance in igneous rock of the earth's crust: 4 × 102 ppm by wt; concentration in the atmosphere: 93.40 ppm by vol.
Discovered in 1894 by Rayleigh and Ramsay. Obtained commercially
from the atmosphere by distillation-liquefaction process. Monograph:
Argon, Helium and the Rare Gases Vols. 1 2,, G. A. Cook, Ed. (Interscience, New York,
1961) 818 pp. Reviews: A. H. Cockett, K. C. Smith, “The
Monatomic Gases” in Comprehensive Inorganic
Chemistry vol. 1, J. C. Bailar, Jr. et
al., Eds. (Pergamon Press, Oxford, 1973) pp 139-211; S.-C. Hwang,
W. R. Weltmer, Jr. in Kirk-Othmer Encyclopedia
of Chemical Technology vol. 13 (John Wiley
& Sons, 4th ed., 1995) pp 1-38; Chemistry
of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon
Press, New York, 1984) pp 1042-1059. Review of use in inductively
coupled plasma-mass spectrometry: S.
F. Durrant, Fresenius J. Anal. Chem. 347, 389-392
(1993).
Properties
Colorless, odorless, tasteless, monatomic, inert
gas; will form compds with highly electronegative elements such as
O, F, Cl. Atomic radius 1.92 × 108 cm. Triple pt temp
83.80 K, press 68.90 kPa. Critical temp 150.86 K, critical press
4898 kPa, critical d 535.7 kg/m3. Non-flammable. Gas: d0 (101.3 kPa) 1.7838 kg/m3, d (normal bp) 5.767 kg/m3. Liquid: normal bp 185.87°, d (normal bp) 1393.9 kg/m3, d (triple pt) 1415 kg/m3, heat of vaporization (normal bp) 6469 J/mol. Solid:
d (triple pt) 1623 kg/m3, heat of vaporization (triple pt) 7.785 kJ/mol, heat of fusion
(triple pt) 1.191 kJ/mol, exists as face-centered cubic crystals at
normal pressure. Soly of gas in water (20°): 33.6 cc/kg water.
Sol in organic liquids.Caution
Can act as a simple asphyxiant by
displacing air. See: Matheson
Gas Data Book (Matheson Co., Inc., 4th ed., East Rutherford,
NJ, 1966) pp 23-28.Use
Gas as shield in gas metal-arc welding, in metal
processing; carrier in gas-liquid and gas-solid chromatography; gas
filler for incandescent light bulbs. Gas in fluorescent tubes analogous
to neon lights, but produces a blue-purplish light; in rectifier tubes;
in thermometers above mercury; in lasers; wherever an inert atmosphere
is desired and the much cheaper nitrogen cannot be used; in ionization
chambers and particle counters; in mixtures with He and Ne in Geiger
counters; in argon-oxygen-decarburizing process for stainless steel;
in manuf of semiconducting devices; in gas mixtures as the working
fluid in plasma arc devices. Liquid as cryogen to produce low temps.
The isotope
40Ar is always found in minerals contg potassium,
since it is a product of
40K decay; measuring the amount
of
40Ar and
40K can be used for determining
the geologic age of minerals and meteors.