Question

Draw diagrams showing the formation of a double bond and a triple bond between carbon atoms in $C_2H_4$ and $C_2H_2$ molecules.

Answer 1

$C_2H_4$ :
The electronic configuration of $C-atom$ in the excited state is:
$_6C$=$1s^2 2s^1 2p_x^1 2p_y^1 2p_z^1$

In the formation of an ethane molecule $(C_2H_4)$, one $sp ^2$ hybrid orbital of carbon overlaps a $sp ^2$ hybridized orbital of another carbon atom, thereby forming a $C-C$ sigma bond.
The remaining two $sp ^2$ orbitals of each carbon atom form a $sp ^2$ $-s$ sigma bond with two 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 $\pi-bond$.

$C_2H_2$:
In the formation of $C_2H_2$ molecule, each $C-atom$ is $sp$ hybridized with two $2p-orbitals$ in an 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 $\sigma$ bond.
The two unhybridized $2p-orbitals$ of the first carbon undergo sidewise overlap with the $2p\; orbital$ of another carbon atom, thereby forming two $pi (\pi)$ bonds between carbon atoms.
Hence, the triple bond between two carbon atoms is made up of one sigma and two $\pi-bonds$.