Question

Explain the bond formation in acetylene.

Answer 1

Similar to ethylene, the bonding in acetylene can also be explained using the hybridization concept. The molecular formula of acetylene is C₂H₂. The electronic configuration of valence shell of carbon in ground state is [He] 2s² 2p_x¹ 2p_y¹ 2p_z⁰. To satisfy the valency of carbon promote an electron from 2s orbital to 2pz orbital in the excited state.

In acetylene molecule, both the carbon atoms are in sp hybridized state. The 2s and 2p_x orbitals, resulting in two equivalent sp hybridized orbitals lying in a straight line along the molecular axis (x-axis). The unhybridized 2p_y and 2p_z orbitals lie perpendicular to the molecular axis.

Formation of sigma bond:

One of the two sp hybridized orbitals of each carbon linearly overlaps with each other resulting in the formation a C – C sigma bond. The other sp hybridized orbitals of both carbons linearly overlap with the two 1s orbitals of two hydrogen atoms leading to the formation of one C – H sigma bond on each carbon.

Formation of pi bond:

The unhybridized 2p_y and 2p_z orbitals of each carbon overlap sideways. This lateral overlap results in the formation of two pi bonds (p_y – p_y and p_z – p_z) between the two carbon atoms as shown in the figure.