Draw diagrams showing the formation of a double bond and a triple bond between carbon atoms in C₂H₄ and C₂H₂ molecules.

Case I:

C₂H_4: The electronic configuration of C-atom in the excited state is:

6C=1s²2s¹2px¹2py¹2pz¹

For the formation of the ethane molecule, one sp² hybrid orbital of carbon overlaps another sp² hybridised carbon orbital, forming a C-C sigma bond and the remaining two sp² orbitals of each carbon forms a sp²s sigma bond with the hydrogen atoms.

The unhybridized orbital of one carbon atom undergoes sidewise overlap with the orbital of a similar kind present on another carbon atom to form a weak π-bond.

CASE II:

C₂H₂ : In the formation ethane molecule, each of the C atoms is sp hybridized with two 2-p orbitals in the unhybridized state.

One sp orbital of each carbon atom overlaps with the other along the internuclear axis forming a C–C sigma bond. The second sp orbital of each C–atom overlaps a half-filled 1s-orbital to form a σ bond.

The two unhybridized 2p-orbitals of the first carbon undergo sidewise overlap with the 2p orbital of another carbon atom, thereby forming two pi bonds between carbon atoms. Hence, the triple bond between two carbon atoms is made up of one sigma and two π-bonds.