Modern inorganic chemistry

346 GROUP VII-THF HALOGENS

only commercially available interhalogen compound) and bromine.

BrF 3. These compounds, which react explosively with water, wood,

rubber and other organic material—and even with concrete and

asbestos—are used to fluorinate compounds, for example actinides

to produce the hexafiuorides (the most important being uranium

hexafluoride, UF 6 ) and chlorinated hydrocarbons to produce

chlorofluorocarbon lubricating oils. Bromine trifluoride has inter-

esting properties as a polar solvent; it undergoes slight ionisation

thus:

2BrF 3 =± BrF 2 +

Polyhalides

The best known polyhalide is the triiodide ion, 1^, found when

iodine dissolves in the aqueous solution of the iodide of a large

unipositive cation (usually K+):

Iodine monochloride, formed when iodine reacts with the iodate(V)

ion in the presence of an excess of concentrated hydrochloric acid,

IOJ 4- 2I 2 + 6H+ + 5CT -» 5IC1 4- 3H 2 O

dissolves in the presence of excess chloride:

ici + cr ^ ici;

Other polyhalides, all singly charged, are formed from one halide

ion together with other halogen or interhalogen molecules adding

on, for example [ClIBr]~, [IC1 4 ]~. Many of these ions give salts

with the alkali metal cations which, if the metal ion is large (for

example the rubidium or caesium ion), can be crystallised from

solution. The ion ICl^ is known in the solid acid, HIC1 4 .4H 2 O,

formed by adding iodine trichloride to hydrochloric acid. Many

other polyhalide ions are less stable and tend to dissociate into the

halide and interhalogen compound.

USE OF HALOGENS AND THEIR COMPOUNDS

FLUORINE

Fluorine in the free state is too reactive to be of a direct practical
value, but it may be used to prepare other compounds of fluorine,
which are then used as fluorinating agents, for example chlorine