Question

How many sigma and pi bonds are present in the molecule given below:
$C{{H}_{2}}=C=CH-C{{H}_{3}}$
(A) sigma $C-C$ bonds = 5, sigma $C-H$ bonds = 5, pi $C-C$ bonds = 4
(B) sigma $C-C$ bonds = 3, sigma $C-H$ bonds = 6, pi $C-C$ bonds = 2
(C) sigma $C-C$ bonds = 4, sigma $C-H$ bonds = 5, pi $C-C$ bonds = 2
(D) sigma $C-C$ bonds = 4, sigma $C-H$ bonds = 6, pi $C-C$ bonds = 4

Answer 1

Sigma bonds are formed by axial or head-on overlapping of atomic orbitals, and pi bonds are formed by lateral overlapping of the atomic orbitals. Sigma bonds are formed along the direction of the internuclear axis.

Complete step by step answer:
Covalent bonds are formed when sharing of electrons between two atoms takes place. Covalent bonds are formed by overlapping of atomic orbitals.
Sigma bonds are those which are formed by axial overlapping or head on overlapping of s and p- orbitals. The electrons participating in a sigma bond are commonly referred to as sigma electrons. Generally all single bonds are sigma bonds.
Pi bonds are formed by lateral overlapping of the p and d-orbitals along the direction perpendicular to the internuclear axis. During the formation of pi bonds, the axes of the atomic orbitals are parallel to each other whereas the overlapping is perpendicular to the internuclear axis. Generally, double bonds consist of one sigma bond and one pi bond, whereas a triple bond is made of two pi bonds and one sigma bond.
The given compound $C{{H}_{2}}=C=CH-C{{H}_{3}}$, has 6 sigma bonds between $C-H$, 3 sigma bonds between $C-C$, 2 pi bonds between $C-C$.
Therefore, the B option is the correct answer.

Note: Covalent bonds are of many types, viz, sigma bonds, pi bonds, coordinate bonds, delta bonds. Sigma bonds are strongest covalent bonds, owing to the direct overlapping of the participating orbitals. Pi bonds are generally weaker than sigma bonds, owing to the significantly lower degree of overlapping.