Hybridization
(a) The concept of hybridization was introduced by Pauling.
(b) Hybridization is defined as the intermixing of dissimilar
orbitals of the same atom but having slightly different energies to form same
number of new orbitals of equal energies and identical shapes.
(c) The new orbitals so formed are known as hybrid orbitals
whose shape is similar to p orbital except that the two lobes are unequal in
size i.e. one lobe is smaller while the other is bigger as shown below :
Rules of Hybridization
(i) Only orbitals (atomic) of nearly same energy belonging to
same atom or ion can take part in hybridization.
(ii) Number of the hybrid orbitals formed is always equal to
number of atomic orbitals which have taken part in the process of
hybridization.
(iii) Most of the hybrid orbitals are similar but they are
not necessarily identical in shape. They may differ from one another in
orientation in space.
(iv) Actually the orbitals which undergo hybridization and
not the electrons.
Types of hybridization
Depending upon the type and number of orbitals involved in
intermixing, the hybridization can be of various types namely sp, sp2,
sp3, sp3d, dsp2, sp3d2,
sp3d3. The nature and number of orbitals involved in the
above mentioned types of hybridization and their acquired shapes are
dissociated as follows:
1. sp hybridization:
a) When one s and one p orbital belonging to the same main
shell of an atom mix together to form two new equivalent orbitals, the type of
hybridization is called sp hybridization or diagonal hybridization.
(b) The new orbitals formed are called sp hybrid orbitals.
(c) They are collinear with an angle of 180° as shown in
figure.
(d) Each orbital has 50% s-character and 50% p-character.
2. sp2
hybridization:
a) When one s and two p-orbitals of the same shell of an atom
mix to from three new equivalent orbitals, the type of hybridization is called
sp2 hybridization or trigonal hybridization.
(b) The new orbitals formed are called sp2 hybrid
orbitals.
(c) All the three hybrid orbitals remain in the same plane
making an angle of 120° with one another as shown in figure.
(d) Each of the hybrid orbitals formed has 1/3rd s character
and 2/3rd p-character.
3. sp3
hybridization:
a) When one s and three p-orbitals belonging to the same
shell of an atom mix together to form four new equivalent orbitals the type of
hybridization is called sp3 or tetrahedral hybridization.
(b) The new orbitals are called sp3 or tetrahedral
orbitals.
(c) These are directed towards the four corners of a regular
tetrahedron and make an angle of 109°28’ with one another as shown in figure.
(d) Each sp3 hybrid orbital has 25% s-character
and 75% p-character.
4. sp3d
hybridization:
This can be understood taking example of PCl5.
(a)
Electronic
configuration of phosphorous in ground state
(c) Now there are five orbitals:
One s, three p (px, py, pz)
and one ( dz2 -orbital) which are singly filled.
(d) These orbitals hybridize to yield a set of five sp3d
hybrid orbitals.
(e) The resultant shape is trigonal bipyramidal.
(f) There are two sets of equivalent hybrid orbitals: one set
consists of three coplanar (120°) equivalent equatorial ‘e’ sp2
orbitals and the other consisting of two equivalent axial ‘a’
dp orbitals as shown in figure
Shape of PCl5 molecule
(Trigonal bipyramidal)
5. sp3d2 Hybridization:
This is explained by taking case of SF6
(a) In sulphur two electrons (one 3s and one 3p) are promoted
to empty dz2 and dx2-y2 orbitals.
(b)Ground state configuration of S
These orbitals yield a set of six sp3d2
hybridized orbitals directed towards the corners of a regular octahedron as
shown below.
