THE NOBLE GASES 355The other noble gases (except radon) are obtained from liquid air,
which can readily be separated into liquid nitrogen (b.p. 77 K)
and oxygen (b.p. 90 K) by fractionation. Helium and neon are found
in the nitrogen fraction, and argon, krypton and xenon with the
oxygen. Argon, containing only a little oxygen, is obtained by
further fractionation, and the remaining oxygen is removed by
burning with hydrogen or by passage over hot copper. Krypton and
xenon are obtained by fractionation over activated charcoal, and
neon and helium are separated in a similar manner. Small amounts
of radon are contained in the gas pumped off from acidified radium
chloride solution; oxygen, carbon dioxide and water are removed
from it by ordinary chemical methods. The radon is frozen and any
other gases can then be drawn off, leaving pure radon.
CHEMICAL PROPERTIES (2)
Following Bartletfs discovery of xenon hexafluoroplatinate(VI),
xenon and fluorine were found to combine to give several volatile,
essentially covalent fluorides, and at least one fluoride of krypton
has been obtained. From the xenon fluorides, compounds containing
xenon-oxygen bonds have been made; much of the known chemistry
of xenon is set out in Figure 12.1.
It can be seen that xenon has valencies or oxidation states of 2, 4,
6 and 8; compounds with xenon in higher oxidation states areXeF 2 xenon difluoride+ F, I + F 2 in electric discharge
h heated tube «,Xexenon tetrafluoride \v + p 2 , heat under pressureY 17 through heated tube ,,
vhydrolysis
hydrolysis >XeOsJ V hydrolysis ^ 1 • XeOF ^ (^4) ° -• XeF 6
xenon trioxide xenon hexafluoride
. heat 4- metal fluoride
dilute NaOH N.OH Mivi Y^F^2 Aer MFg
cone. NaOH H 2 S0 4
NaHXeO 4
I NaOH sodium perxenate xenon ten oxide
Na 2 XeO 4 or xenale(Vlil)
sodium xenatefVI)
figure 12.1