6. Important trends and anomalous properties of carbon

IMPORTANT TRENDS AND ANOMALOUS BEHAVIOUR OF CARBON

Carbon, differs from the rest of the member of its family. The main reason for the anomalous behaviour is:
(i) exceptionally small atomic and ionic size
(ii) higher ionization enthalpy
(iii) absence of d-orbitals in the valence shell.
(iv) Higher electronegativity.

It can be explained as follows:
=> Since carbon has only s and p-orbitals it can accommodate only four pairs of electrons ; other member can expand their covalence due to the presence of d-orbitals.
=> Carbon can form Pπ-Pπ multiple bonds with itself and other atoms having small size and high electronegativity.

For example, C=C, C≡C, C=O, C=S and C≡N

The order of catenation is C >> Si > Ge ≈ Sn

Heavier elements do not form Pπ-Pπ bonds because their atomic orbitals are too
large and diffuse to have effective overlapping.
=> Carbon atoms have the tendency to link with one another through covalent bonds to form chains and rings. This property is called catenation.
Down the group property to show catenation decreases.

C > Si > Ge > Sn > Pb
Lead does not show catenation.