Nomenclature
CAS number: 7440-59-7
Description and 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 ×
104%). Known artificial radioactive isotopes: 5-8.
Longest-lived isotope: 6He (T 806.7 msec, β-emitter).
Abundance in igneous rock of earth's crust: 3 × 103 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, monatomic, inert
gas. Non-flammable. 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
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 liquid forms exist: He I above ≈2.2 K; He II below ≈2.2 K.
He II is a superconducting liquid; has very low viscosity; superfluid.Derivative
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.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 N
2 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.