CHEMICAL PROPERTIES OF CARBON FAMILY
(1) Reactivity
towards acids :C, Si, Ge unaffected by dilute acid but Sn dissolves in dilute HNO3 forming Sn(NO3)2. Pb dissolves slowly in dilute HCl
forming PbCl2 and quite readily in dilute HNO3 forming Pb(NO3)2 and oxides of nitrogen.
Si is
oxidised and undergoes fluorination by hot concentrated HF/HNO3.
Sn
dissolves in several concentrated acids. Pb does not dissolves in concentrated
HCl because a surface coating of PbCl2 is
formed.
(2) Reactivity
towards alkalies :Carbon is unaffected by alkalies. Si reacts slowly with cold aqueous
solution of NaOH and readily with hot NaOH solution giving solution of
silicates [SiO4]4–. Sn and Pb
are amphoteric it dissolves slowly in cold and readily in hot NaOH solution
forming stannates Na2[Sn(OH)6] and plumbates Na2[Pb(OH)6].
(3) Hydrides
: All the elements of group 14 combine with hydrogen
directly or indirectly to form the covalent hydrides,
(M = C, Si, Ge, Sn or
Pb). The number of hydrides and the ease of preparation decrease on going from
carbon to lead.
The
hydrides of silicon are called silanes having the general formula
. The hydrides of germanium are called germanes while those
of tin are called the stannanes. Only lead forms an unstable hydride of the
formula,
called the plumbane.
Three
hydrides of germanium, i.e.,
and
and only two hydrides
of tin i.e.
and
are well known.
(4) Oxides
: Carbon forms five oxides
(carbon suboxide),
and
is the anhydride of
malonic acid and
is the anhydride of
(carbonic acid).
is a non-polar linear molecule due to maximum tendency of C
to form pp–pp
multiple bond with oxygen. Si forms
. Pb forms a number of oxides. PbO can be obtained by heating
.
.
The
red form of PbO is called litharge
and the yellow form is massicot.
(Red lead, or Sindur) is prepared by heating litharge in air
at 470°C,
Note
:
and
are all solids.
and
is acidic,
is weakly acidic while
and
are amphoteric in
nature. All the elements of group 14 except silicon from monoxides e.g.,
and PbO. Out of these
monoxides only CO is neutral, while all other monoxides are basic.
(5) Halides
: Elements of group 14 react with halogens directly to
form tetrahedral and covalent halides except C where its halide is produced by
the action of halogens on hydrocarbons.
and
do not exist because
is a strong oxidant and
and
are strong reductants.
Hence
ion is difficult to
survive in presence of strong reductants
and
and is immediately reduced
to
.
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