Engineering Chemistry S Datta

VALENCY AND CHEMICAL BONDING 21
H
H
C
H
H
Fig. 2.9 CH 4
molecule.
sp 2 -hybridization
Electronic configuration of :
C in the ground state
1s 2s 2p
C in the excited state
Four unpaired
electrons
One 2s
and two 2p
electrons
hybridize to give
sp 2 hybridization
2p
2s and two of 2p orbitals hybridize instead of three 2p orbitals to form three sp 2 hybrid orbitals
because the three hybrid orbitals are much more directed. The hybrid orbitals lie in a plane
and the axes are directed towards vertices of an equilateral triangle and so, bond angle in this
case is 120°. Three sp 2 hybrid orbitals of each C-atom form three sigma bonds in ethylene
molecule.
H
H
C
C
-bond
H
H
-bond
Fig. 2.10 Ethylene molecule.
-bond
Lateral overlapping of the two 2p orbitals of two C-atoms leads to the formation of a
weak bond known as π-bond (See Fig. 2.10).
Highlights:
• Ethylene molecule contains five sigma bonds.
• Four sigma bonds are formed due to overlapping of sp 2 -s orbitals and one out of
sp 2 -sp 2 overlapping. Residual 2p orbitals of each sp 2 hybridised C-atom overlap
laterally to form a π-bond (Fig. 2.10).