Structural Formula Vector Image
Title: Helium
CAS Registry Number: 7440-59-7
Literature References: He; at. wt 4.002602; at. no. 2. 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. Natural isotopic mixture (mass numbers): 4 (99.999862%), 3 (1.38 ´ 10-4%). Known artificial radioactive isotopes: 5-8. Longest-lived isotope: 6He (T½ 806.7 msec, b-emitter). Abundance in igneous rock of earth's crust: 3 ´ 10-3 ppm by wt; concentration in air: 5.24 ppm by vol. Identified in the spectrum of the sun's chromosphere by Lockyer and Frankland in 1868. Obtained by Hillebrand in 1890 by heating uranium minerals and identified by Ramsay in 1895. Found in natural gas from which it is extracted on a commercial scale. Produced in the decay of radioactive elements: 1 kg of uranium in its conversion into 865 g of lead forms 756 l of helium; also produced in nature by the bombardment of beryllium, lithium, and other light elements with cosmic rays, x-rays and high-speed protons and deuterons. Monograph: G. A. Cook, Argon, Helium and the Rare Gases (Interscience, New York, 1961). Reviews: 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; E. Cook, Science 206, 1141-1146 (1979); 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, nonflammable, monatomic, inert gas; will form compds with highly electronegative elements such as O, F, Cl. Cannot be frozen by lowering the temp at ordinary press.; no triple point. Very slightly sol in water (ml/100 ml): 0.97 at 0°; 1.08 at 50°. Trouton's const 4.64.
Derivative Type: 4He
Properties: Critical temp 5.2014 K, critical press 227.5 kPa, critical d 69.64 kg/m3. Gas: d0 (101.3 kPa) 0.17850 kg/m3, d (normal bp) 16.89 kg/m3. Liquid: normal bp -268.926°, d (normal bp) 125.0 kg/m3, heat of vaporization (normal bp) 81.70 J/mol. Two liq forms exist: He I above ~2.2 K; He II below ~2.2 K. He II is a superconducting liq; has very low viscosity; superfluid.
Boiling point: bp -268.926°
Density: d 69.64 kg/m3; d0 (101.3 kPa) 0.17850 kg/m3; d (normal bp) 16.89 kg/m3; d (normal bp) 125.0 kg/m3
Derivative Type: 3He
Properties: Critical temp 3.324 K, critical press 116.4 kPa, critical d 41.3 kg/m3. Gas: d0 (101.3 kPa) 0.1347 kg/m3, d (normal bp) 23.64 kg/m3. Liquid: normal bp -269.959°, d (normal bp) 58.9 kg/m3, heat of vaporization (normal bp) 25.48 J/mol.
Boiling point: bp -269.959°
Density: d 41.3 kg/m3; d0 (101.3 kPa) 0.1347 kg/m3; d (normal bp) 23.64 kg/m3; d (normal bp) 58.9 kg/m3
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 249-253.
Use: Liquid helium (the most volatile liq known) as cryogen for the production of low temps, in MRI machines. Gas in manuf of semiconducting devices; in detection devices for leaks in vacuum systems; in Ne-He lasers; in gas mixtures as the working fluid in plasma devices; in mixtures with Ne and Ar in Geiger counters. Q-Gas, a mixture of 98.7% He and 1.3% butane, has been used as a filling for gas-flow Geiger counters. Gas as a shield in gas tungsten-arc welding, in metal processing; substitute for N2 in synthetic breathing gas for deep sea divers and workers in high pressure conditions; coolant in high temp nuclear reactors; carrier gas in gas-liquid and gas-solid chromatography; inert diluent; to create inert atmosphere; to fill balloons and airships, lifting power is 0.93 if hydrogen is taken as 1.00.

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