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Encyclopedia of Physical Science and Technology EN010K-480 July 16, 2001 17:22

Noble-Gas Chemistry

Gary J. Schrobilgen
McMaster University

I. Historical Background
II. Preparative Methods for the Binary Fluorides
III. Xenon Compounds
IV. Krypton Compounds
V. Radon Compounds
VI. Prospects for Argon Compounds
VII. Applications

GLOSSARY pressurizing liquid fuel rockets and for filling balloons
and lighter-than-air craft. Helium has the ground state
2
Argon, Ar At. no. 18, at. wt 39.948, mp −189.2 C, bp electronic configuration 1s and has no normal chem-
◦
◦
−185.7 C. Argon is the most abundant of the noble istry, although excited state species containing bound
gases (0.93% of dry air) and is used in light bulbs, as He are formed in discharge tubes. Liquid He has no
an inert shield in arc welding, and for metal production triple point and cannot be solidified at atmospheric
(Ti, Si). Argon has the ground state electronic config- pressure. Liquid He II exhibits superconductivity and
6
2
uration [Ne]3s 3p and forms some clathrates but no can flow against gravity over the edge of vessels. It
stablebulkcompounds,exceptexcitedstatespeciesand changes to He I at 2.2 K.
one species isolated in a low-temperature argon matrix, Krypton, Kr At. no. 36, at. wt 83.80, mp −156.6 C, bp
◦
−3
HArF. −152.3 C. Krypton (1.14 × 10 % in dry air) is used
◦
Element-118 See ununoctium. (with Ar) for fluorescent lights, high-intensity minia-
Helium, He At. no. 2, at. wt 4.00260, mp −272.2 C, ture incandescent lamps, and in certain photographic
◦
bp −268.934 C. Helium is one of the noble gases flash lights. The ground state electronic configuration
◦
6
2
−4
(5.2 × 10 % in dry air and up to 7% in some natu- is [Ar]4s 4p . Krypton forms a limited range of com-
ral hydrocarbon gases). It is found in some radioac- pounds containing Kr F, Kr O, and Kr N bonds and
tive minerals as a product of radioactive decay (the some clathrates. Among the chemical compounds it
α-particle is an He 2+ cation) and is separated by lique- forms are linear krypton difluoride, KrF 2 (formed by
faction. Helium is used to provide an inert atmosphere the low temperature reaction of Kr with F atoms that
for arc welding and for Ti, Zr, Si, Ge production; as are formed by dissociation of F 2 under photolytic, elec-
a coolant in the liquid state for superconducting mag- tric discharge, or thermal conditions), Kr(OTeF 5 ) 2 , and
−
+
nets; with 20% O 2 as an atmosphere for divers; and for HCNKrF AsF . Krypton difluoride also reacts with
6
. 449