118.

Discuss the characteristics of group 14 elements in terms of:
(i) Atomic radius 
(ii) Ionisation enthalpy
(iii) Electropositive character
(iv) Melting and boiling points.

(i) Atomic radius: Atomic radius of these elements show a regular increase from carbon to lead. This is due to the addition of an extra shell in each succeeding element. However, the increase in the atomic radii from Si onwards is small. This is due to the ineffective shielding of valence electrons by the intervening d and f-orbitals.

(ii) Ionisation enthalpy: The ionisation enthalpy of these elements decrease as we move from carbon to lead. This is due to the increase in atomic size because of which nuclear pull on the outermost electrons decreases down the group.
However, the first ionisation enthalpy of these elements are higher than the corresponding elements of group 13. This is due to the higher nuclear charge and smaller size of atoms of group 14 elements.

(iii) Electropositive character: Due to high ionisation energies, the elements of group 14 are less electropositive as compared to group 13 elements. On moving down the group, the electropositive character increases due to the decrease in ionisation energies.

(iv) Melting and boiling points: There is a regular decrease in the melting and boiling points as we move down the group i.e. from carbon to lead. This is because as we move down the group, the size of the atoms increases and hence, interatomic forces of attraction decrease. As a result, lesser amount of energy is needed to melt or boil them.