356 THE NOBLE GASES
powerful oxidising agents, for example xenate(VIII) will oxidise a
manganese(II) salt to manganese(VII) salt. All the fluorides are readily
hydrolysed to give, finally, xenon gas and hydrofluoric acid; hence
hydrolysis is a means of analysis. The xenon fluorides are solids;
xenon trioxide is a white, explosive solid, while xenon tetroxide is a
gas.
The structures of the three xenon fluorides are:Fthe exact position of the single lone pair in xenon hexafluoride being
uncertain. These structures may be compared with those of the poly-
Ealide ions; XeF 2 is linear like [IC1 2 ] ~, XeF 4 is planar like [IC1 4 ] ~.
Now an ion [I (halogen)J~ is isoelectronic with (has the same
total number of electrons as) a molecule Xe (halogen)x, and hence
similarity between the two kinds of structures is to be expected;
this means that xenon is behaving in some ways like (iodine -f one
electron). Hence we are justified in putting the noble gas group next
to the Group VII halogens, rather than before Group I.
In xenon difluoride, the electronic structure shows three lone
pairs around the xenon, and two covalent bonds to the two fluorine
atoms; hence it is believed that here xenon is using one p (double-
pear) orbital to form two bonds:Freezing of water in presence of noble gases such as krypton
and argon leads to the formation of noble gas hydrates, which
dissociate when the temperature is raised. Here the noble gas atoms
are 'caged' in holes in the ice-like lattice; we have seen (p. 323)
that chlorine molecules can be trapped in relatively large holes in this
kind of lattice, and the smaller noble gas atoms are accommodated
both in these and also in some smaller holes to give a limiting com-
position X.5.76H 2 O. If a hot solution of benzene-1,4-diol (para-
quinol) C 6 H 4 (OH) 2 , is cooled in an atmosphere of argon or krypton
(under pressure) three molecules of the quinol unite on crystallisa-