When different atomic orbitals of similar energy intermix to give new hybrid orbitals of similar energy and shape (degenerate hybrid orbital’s), the phenomenon is known as hybridization. Important conditions for hybridization
(i) The orbitals present in the valence shell of the atom are hybridised.
(ii) The orbitals undergoing hybridization should have almost equal energy.
(iii) Promotion of electron is not essential condition prior to hybridization.
(iv) It is not necessary that only half-filled orbitals participate in hybridization. In some cases, even filled orbitals of valence shell take part in hybridization.
Types of Hybridization
Sp3 hybridization
When 1 S and 3 p orbitals undergo hybridization to give new 4 hybrid orbitals Example
CH4
Here the ground state electronic configuration of central Carbon atom is
2s2 ,2p2.
In the excited state, one of the 2s electrons is promoted to vacant 2p orbital as (s,+px +py + pz)
Sp2 hybridization
When 1 S and 2p orbital hybridize to give 3 hybrid orbitals’, hybridization is Sp2.
Example
BCl3
Here the ground state electronic configuration of central boron atom is
1s2 ,2s2 ,2p1.
In the excited state, one of the 2s electrons is promoted to vacant 2p orbital as (s +py + pz)
s – p hybridization
When 1 S orbital and 1 p orbital hybridize to give 2 hybridization orbitals hybridization is Sp.
Example
C2H2
This can be understood with below steps
1) both the carbon atoms undergo sp-hybridisation having two unhybridised orbital i.e., 2py and 2px.
2) One sp hybrid orbital of one carbon atom overlaps axially with sp hybrid orbital of the other carbon atom to form C C sigma bond, while the other hybridised orbital of each carbon atom overlaps axially with the half filleds orbital of hydrogen atoms forming sigma bonds.
3) Each of the two unhybridised p orbitals of both the carbon atoms overlaps sidewise to form two pie bonds between the carbon atoms.
4) Therefore the triple bond between the two carbon atoms is made up of one sigma and two pi bonds
