Argon. Ar; at. wt. 39.948; at. no. 18. Three stable isotopes: 36 (0.337%); 38 (0.063%); 40 (99.600%); artifical,
radioactive isotopes: 33; 35; 37; 39; 41; 42. Abundance in earth's crust: 4 x 104%; concentration in
the atmosphere: 0.93% by vol; cosmic abundance: ~1.5 x 105 atom/106 atoms of Si. Elemental,
monoatomic, gaseous constituent of air, discovered by Rayleigh and Ramsay in 1894. Although molecular ions, hydrates
and clathrates of argon have been observed, it should be considered a "noble", chemically inerts gas, due to its
electronic structure. The outer p subshell is entirely filled:
1s22s22p63s23p6. Obtained commercially during liquid-air
manufacture. A radioactive isotope 41Ar (110 min, b-) is found in
the air surrounding atomic reactors, when n,g reaction is
possible. Monograph: Argon, Helium and the Rare Gases, vol. 1, 2, G.A. Cook, Ed. (Inerscience,
New York, 1961) 818 pp. Review: Cockett, Smith, "The Monatomic Gases" in Comprehensive Inorganic Chemistry,
vol. 1, J. C. Bailar, Jr. et al., Eds (Pergamon Press, Oxford, 1973) pp 139-211.
Colorless, odorless, inert gas. d° (gas) 1.784 g/l. bp -185.86° (87.29°K); crit temp -122.3°; critical press 48.3 atm.
Crystallizes in a face-centered cubic lattice; triple pt -189.37° (83.78°K). d (solid at triple pt) 1.623. Atomic radius
1.92 x 10-8 cm. Soly of gas in water at 20°: 33.6 cc/kg water. Also sol in organic liquids.
USE: In fluorescent tubes analogous to neon lights, but produces a bluish-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. 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. Human Toxicity: Simple asphyxiant.
Ref.: 808, pp 123-124.
The Merck Index - Eleventh Edition.
Copyright © 1989 by Merck & Co., Inc.