sp3Hybridisation
In this hybridisation one '2s' and three '2p' orbitals present in the valence shell of the excited carbon atom get hybridised to give rise to four new orbitals of equivalent energies. Each sp3 hybrid orbital is an average of one '2s' orbital and three '2p' orbital having one fourth s character and three fourth p character. The original '2s' orbital is spherically symmetrical (non-directional) while the three '2p' orbitals are dumb bell shape (directional) orienting along the three axes perpendicular to each other. But the newly formed sp3 hybrid orbitals consist of two lobes one big and the other small. These orbitals tend to lie as far apart in space due to mutual repulsion of the electron clouds in them. They get directed towards the four corners of a regular tetrahedron with the carbon atom in the center. Therefore this hybridisation is also called as tetrahedral hybridisation with an angle of 109.5 between the hybrid orbitals.
Fig: 6.6 - Representation of sp3
hybridisation
Illustration: Methane - CH4
In methane, the carbon atom undergoes sp3 hybridisation and forms four sp3 hybridised orbitals. Each of the hybrid sp3 orbitals of carbon overlaps axially with half filled '1s' orbital of hydrogen atom forming four sigma bonds. The four sp3 orbitals are directed towards the corner of a regular tetrahedron making an angle of 109.5o.
Fig: 6.7 - Orbital picture and structure of methane
sp2hybridisation
In this type of hybridisation one '2s' and two 'p' orbitals (2px and 2py) get hybridised to form three equivalent orbitals called 'sp2' hybrid orbitals. Each hybrid orbital has one third 's' character and two third 'p' character. The bond angle between the two hybridised orbital is 120. The unhybridised orbital (2pz) of carbon is oriented in a plane at right angles to the plane containing the three hybridised orbitals.
1s 2s 2px 2py 2pz
Fig: 6.8 - Representation of sp2hybridisation
Illustration: Ethene - C2H6
In the formation of ethylene, each carbon atom undergoes sp2 hybridisation leaving 2pz orbital unhybridised. One of the sp2 hybridised orbital of one carbon atom overlaps axially with sp2 hybridised orbital of the other carbon atom to form a stable sigma bond (C-C). The remaining two sp2 hybrid orbitals of both carbon overlap axially with the half filled '1s' orbital of hydrogen atoms forming four C-H sigma bonds. The unhybridised orbital (2pz) of one carbon atom overlaps sidewise with the similar orbital of the other carbon atom to form a weak pi bond. Thus, in ethylene all the six atoms containing the sigma bonds lie in one plane while the pi bond is at a plane perpendicular to the plane of the six atoms.
Fig: 6.9 - Orbital picture of ethylene
'sp' hybridisation
In this type of hybridisation one '2s' and one '2px' orbitals get hybridised to form two equivalent orbitals called 'sp' hybrid orbitals. The remaining 2py and 2pz do not take part in hybridisation. The two unhybridised orbitals are directed along the 'y' and 'z' axes while the two hybridised orbitals are directed towards the 'x' axis. This hybridisation is often known as diagonal hybridisation as the two hybridised orbitals are at 180o due to mutual repulsion of their electron clouds. Each hybrid orbital has equal 's' and 'p' character.
Fig: 6.10 - Representation of sp2hybridisation
Illustration: Ethyne - C2H2
In the formation of ethyne both the carbon atoms undergo 'sp' hybridisation leaving two unhybridised orbitals on each (2py and 2pz). One 'sp' hybrid orbital of one carbon atom overlaps axially with the 'sp' hybrid orbital of the other carbon atom to form C-C sigma bond. The remaining hybridised orbital of each carbon atom overlap axially with half filled orbital of hydrogen forming sigma bond. Each of the two unhybridised orbitals of one carbon atom overlaps sidewise with the similar orbitals of the other carbon atom to form two pi bonds.
