Modern inorganic chemistry

GROUP IV 197

SiCl 4 + 2H 2 O -> 4HC1 + SiO 2 i

Silica gel is again obtained but silicon does not form the corres-

ponding hexachlorosilicic acid since the small silicon atom is

unable to coordinate six chlorine atoms.

Silicon difluoride is obtained as a very reactive gas when silicon

tetrafluoride and silicon are heated together. It polymerises rapidly

to give (SiF 2 )n, a solid.

Germanium

Germanium forms divalent compounds with all the halogens.
Germanium(ll) chloride can be prepared by passing the vapour of
germanium(IV) chloride (see below) over heated germanium. The
reaction is reversible and disproportionation of germanium(II)
chloride is complete at about 720 K at atmospheric pressure:

GeCl 4 + Ge ^ 2GeCl 2

(Germanium(II) fluoride can be prepared by a similar process using
a slightly lower temperature.)
Germanium(II) chloride is hydrolysed by water; the reaction can
be represented as

GeCl 2 + 2H 2 O -> Ge(OH) 2 + 2HC1

but the product Ge(OH) 2 may be a hydrated oxide. With hydrogen

chloride gas, the reaction is an addition :

GeCl 2 -I- HC1 -> GeCl 3 H [analogous to trichloromethane,

(chloroform) CC1 3 H]

In concentrated hydrochloric acid solution, the reaction is

GeCl + Cl" ->[GeCl 3 ]-

and salts of this anion are known.

Germanium(IV) chloride can be prepared by passing chlorine over

germanium at a temperature of 37CM50 K :

Ge + 2C1 2 -> GeCl 4

It has a covalently bonded structure and is a colourless liquid at
room temperature; it is hydrolysed reversibly by water, all the
germanium being recoverable by distilling the product with con-
centrated hydrochloric acid :GeCl 4 4- 2H 2 O — GeO 2 4- 4HC1