Structural Formula Vector Image
Title: Argon
CAS Registry Number: 7440-37-1
Literature 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 (T½ 269 years, b-emitter). Abundance in igneous rock of the earth's crust: 4 ´ 10-2 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 ´ 10-8 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. 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.
Boiling point: bp -185.87°
Density: d 535.7 kg/m3; d0 (101.3 kPa) 1.7838 kg/m3; d (normal bp) 5.767 kg/m3; d (normal bp) 1393.9 kg/m3; d (triple pt) 1415 kg/m3, heat of vaporization (normal bp) 6469 J/mol; 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
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.

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