a. i. The strength of the bond depends on the extent of overlap of the orbitals. Greater the overlap, stronger is the bond.
ii. A sigma bond is formed by the coaxial overlap of the atomic orbitals which are oriented along the internuclear axis, hence the extent of overlap is maximum.
iii. A pi bond is formed by the lateral overlap of the atomic orbitals which are oriented perpendicular to the internuclear axis, hence the extent of orbital overlapping in side wise manner is less.
Hence,
Sigma bond is stronger than pi bond.
b. i. When a covalent bond is formed between two atoms of different elements that have different electronegativities, the shared electron pair does not remain at the centre.
The electron pair is pulled towards the more electronegative atom resulting in the separation of charges.
ii. In H-F, fluorine is more electronegative than hydrogen.
Therefore,
The shared electron pair is pulled towards fluorine and fluorine acquires partial -ve charge and simultaneously hydrogen acquires partial +ve charge.
This gives rise to dipole and H-F bond becomes polar.
Hence,
H-F is a polar molecule.
c. The electronic configuration of carbon is :
1s2 2s2 2px1 2py1
One electron from ‘2s’ orbital is promoted to the empty ‘2p’ orbital.
Thus,
In excited state,
Carbon has four half-filled orbitals.
Hence,
Carbon can form 4 bonds and is tetravalent in nature.
