Modern inorganic chemistry

GROUP IV 191

and can be cooled without becoming too viscous (hydrocarbon oils

become viscous on cooling); hence silicone oils are used for low-

temperature lubrication. Moreover, silicones are water-repellant,

and have high dielectric constants so that they are useful for electrical

condensers.

Solid, rubbery silicones likewise retain their plasticity at low

temperatures and are resistant to many forms of chemical attack;

they are now incorporated in paints for resisting damp and for

waterproofing. Silicones are also used in moulds to avoid sticking

of the casting to the mould.

Oxides of germanium

GERMANIUM(II) OXIDE, GeO

The existence of germanium(II) oxide is well established. It is a solid

which can be made, for example, by the action of water on ger-

manium dichloride, GeCl 2 :

GeCl 2 + H 2 O -> GeO + 2HC1

The product is a solid yellow hydrated oxide. If prepared by a

method in the absence of water, a black anhydrous product is

obtained. Germanium(II) oxide is stable in air at room temperature

but is readily oxidised when heated in air or when treated at room

temperature with, for example, nitric acid, hydrogen peroxide, or

potassium manganate(VII). When heated in the absence of air it

disproportionates at 800 K:

2GeO -> Ge + GeO 2

The yellow hydrated oxide is slightly acidic and forms germanates(II)

(germanites). The increased stability of germanium(II) oxide com-

pared to silicon(II) oxide clearly indicates the more metallic nature

of germanium.

GERMANIUM(IV) OXIDE

Germanium(IV) oxide occurs in two forms; one has a rutile lattice
and melts at 1359K whilst the other has a quartz lattice and a
melting point of 1389 K. It can be prepared by oxidation of ger-
manium using, for example, concentrated nitric acid, or by the
hydrolysis of germanium tetrachloride:

Ge + 4HNO 3 -> GeO 2 i + 4NO 2 t + 2H 2 O

GeCl 4 + 2H 2 O -> GeO 2 + 4HC1