Synthetic Inorganic Chemistry

CHAPTER IX

ELEMENTS OF GROUP IV OF THE

PERIODIC SYSTEM

This group stands in the middle of the Periodic Table of the

elements, and in it the difference in properties between the elements

of Family A and Family B is at a minimum. Like Group III,

therefore, the whole group is considered under one heading.

The elements of this group which come most to our attention

in everyday life are carbon, silicon, tin, and lead. Carbon and

silicon are the first two members and are exclusively acid-forming

elements, although the acids formed are not strong ones. Tin

and lead are the last two members of Family B and are in the

main base-forming; they are comparable in this respect with the

heavy metals already considered under Groups I and II. In this

group the elements of low atomic weight are exclusively acid-

forming, and the elements of high atomic weight are almost en-

tirely base-forming. Between these extremes there is an almost

regular gradation of properties.

PREPARATION 41
PRECIPITATED SILICA, SiO 2
Carbon dioxide and silicon dioxide are chemically very similar
to each other in that both form weak acids, that of silicon, the
heavier element, naturally being the weaker acid. On the other
hand, these oxides are very dissimilar in their physical properties,
one being a gas, and the other a solid with an extremely high
melting point.
The mineral quartz is crystallized silicon dioxide. Sea sand
consists mostly of rounded grains of broken quartz. If finely
ground quartz or sand is fused for a long time with sodium car-
bonate, the weaker, but non-volatile, acid anhydride displaces
the carbon dioxide, and sodium silicate is obtained. This is a
glass-like substance, which, however, can slowly be dissolved by
water heated under pressure. The solution so obtained is evapo-
rated to a sirup-like consistency and is sold on the market under
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