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

450 Noble-Gas Chemistry

+
Lewis acid fluorides to form KrF and Kr 2 F salts. tium have been directly determined, as only a few
+
3
The KrF cation is the strongest oxidative fluorinating atoms have been produced by this method. It is likely
+
agent known. that element-118 may be a solid at room temperature.
Neon, Ne At. no. 10, at. wt 20.179, mp −248.67 C, bp Like radon, the chemistry of ununoctium is expected
◦
◦
−246.05 C. Neon is a relatively abundant noble gas to reflect its anticipated metalloid properties. The
−3
(1.82 × 10 % of dry air) and is widely used in flu- unconfirmed ground state electronic configuration is
14
2
10
6
orescent tubes (neon lights), Geiger-M¨uller tubes, gas [Rn]5f 6d 7s 7p .
◦
lasers, and electrical equipment. The ground state elec- Xenon, Xe At. no. 54, at. wt 131.29, mp −111.9 C,
6
2
−6
◦
tronic configuration is [He]2s 2p , and Ne forms no bp −107.1 C. Xenon (8.6 × 10 % in dry air) is used
stable chemical compounds. in lamps and discharge tubes and is moderately soluble
Noble gases Sometimes referred to as the rare gases or in water. Xenon exhibits the most extensive chemistry
inert gases (the latter is a misnomer). They are the el- of all the noble gases. It has the ground state elec-
6
2
ements helium, neon, argon, krypton, xenon, radon, tronic configuration [Kr]5s 5p and shows oxidation
1
+
and element-118. All except element-118 occur as mi- states (examples in parentheses) + (Xe ), +2 (XeF 2
2 2
+
+
nor constituents of the atmosphere. Helium, neon, ar- and salts of XeF ,Xe 2 F ), +4 (XeF 4 , XeF salts),
+
3 3
gon, krypton, and xenon are separated by fractiona- +6 (XeF 6 , XeOF 4 , XeO 2 F 2 , XeO 3 , and salts of XeF ,
+
5
−
+
−
−
2−
tion of liquid air. Helium is also a minor component XeOF , XeO 2 F , XeF , XeF , XeOF , XeO 2 F ,
+
3 8 7 5 3
of some natural hydrocarbon gases. They are used and XeO 3 F ), and +8 (XeO 2 F 4 , XeO 3 F 2 , XeO 4 , and
−
(particularly, He and Ar) to provide an inert atmo- salts of XeO 4− and XeO 3 F ). Both XeO 3 and XeO 4
−
3
6
sphere, e.g., for welding, and in electric light bulbs and are treacherous explosives and are exceedingly diffi-
discharge tubes (Ne) and high-intensity photographic cult to handle. Bonds to elements other than xenon,
lamps (Xe). Liquid helium is used in cryogenic applica- oxygen, or fluorine are known, namely, carbon, nitro-
tions, such as the coolant for superconducting magnets. gen, and gold. These are exemplified as the C 6 F 5 Xe ,
+
The amounts of He and Ar formed in minerals by ra- HCNXeF , and AuXe 2+ cations, respectively.
+
4
dioactive decay can be used to determine the age of
a specimen. Xenon, and to a lesser extent Kr and Rn,
have a chemistry; the other noble gases do not form I. HISTORICAL BACKGROUND
bulk chemical compounds, but an example of an argon
compound has been detected in trace amounts at low The noble gases had been characterized for many years as
temperature. inert and incapable of forming compounds with other el-
Radon, Rn At. no. 86, at. wt 222, mp −71 C, bp ements. Numerous attempts to induce chemical reactivity
◦
◦
−61.8 C. Radon is an intermediate radioactive de- over the years led to the myth of their chemical inertness
cay product of 226 Ra. 222 Rn, the most stable isotope and the inviolability of the noble-gas valence shell octet of
of radon, is obtained as a gas from aqueous solutions electrons, the so-called “octet rule.” Several unsuccessful
of 226 RaCl 2 and has been used as a radiation source attempts to synthesize noble-gas compounds were pub-
and as a gaseous tracer. It is a considerable hazard lished in the 1930s, as well as theoretical speculations
in uranium mines. In some areas, radon in basements by Linus Pauling that noble-gas compounds should ex-
and in ground water is a potential health hazard be- ist. Failed attempts to discover noble-gas chemistry likely
cause of its radioactivity. The ground state electronic served to entrench the doctrine of the octet rule. The dis-
6
14
10
2
configuration of radon is [Xe]4f 5d 6s 6p . Because covery of noble-gas reactivity played a key role in inaugu-
radon is intensely radioactive, the chemistry of radon rating a new era in inorganic chemistry. The first authen-
has only been investigated on the tracer scale. Radon tic noble-gas compound was discovered by Neil Bartlett
forms compounds, particularly a fluoride (likely RnF 2 ), in 1962 at the University of British Columbia. He recog-
and solid adducts between the fluoride and Lewis acid nized that molecular oxygen was oxidized by PtF 6 to give
fluorides. O PtF and that PtF 6 must therefore be an oxidizer of
−
+
6
2
Ununoctium, Uuo Name and symbol are temporary; at. unprecedented strength. He also noted that the first ion-
no. 118, at. wt 293. Ununoctium is a synthetic or ization energies of molecular oxygen (1.176 MJ mol −1
−1
+
transuranium element that was first made in 1999 in for O 2 → O + e ) and Xe (1.167 MJ mol ) are very
−
2
86
a cyclotron by the nuclear reaction of 449 MeV Kr + similar and surmised that PtF 6 should also oxidize xenon.
208 293
Pb. The nucleus of 118 decays within less than He proceeded to show that deep red-brown PtF 6 vapor
1 msec by emission of an α-particle into element- spontaneously oxidized xenon gas at room temperature to
116. No physical and chemical properties of ununoc- produce a yellow-orange compound which he formulated