Answer:
In the case of representative
elements, the first element in each of the group, i.e., lithium in the first
group, beryllium in the second group and boron to fluorine in the groups 13 to
17 differ in many respects from the other members of their respective groups.
This behaviour is attributed to following reasons:
(a) small atomic radius of the atom,
(b) high electronegativity,
(c) non-availability of d-orbitals
in the valency shell,
(d) tendency to form multiple
bonds,
(e) high charge/radius ratio.
Examples: Li is the first
member of first group. It shows properties different than other alkali metals
such as:
(a) It does not impart colour to
the flame like other alkali metals.
(b) Its compounds show some what
covalent nature while compounds of alkali metals are ionic.
(c) it is more harder and
lighter than other alkali metals.
(d) It is the only alkali metal
which directly combines with nitrogen.
(e) \[LiHC{{O}_{3}}\] is not
known in solid state as other bicarbonates of alkali metals are known.
Carbon being the first member of
its group shows the following unique properties:
(a) It is the hardest and has
highest melting and boiling points among the elements of group 14.
(b) Its maximum covalency is 4.
(c) It has maximum catenation
property. It can form multiple bonds.
(d) It has highest ionisation
energy and most electronegative element of group 14.
(e) Carbon dioxide, is a gas
while the dioxides of other elements are solids.
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