(B) HYBRIDISATION THEORY
(a) It is introduced by pauling and slater, to explain equivalent nature of covalent bonds in a molecule.
Consider an example of Be compound :-
If it is formed without hybridisation then -
p-s p–p
Cl —— Be ———— Cl
both the Be–Cl bonds should have different parameters and p–p bond strength > s–p bond strength.
Practically bond strength and distance of both the Be–Cl bonds are same.
This problem may overcome if hybridisation of s and p-orbital occurs.
(b) Definition : Mixing of different shapes and approximate equal energy atomic orbitals, and redistribution
of energy to form new orbitals, of same shape & same energy. These new orbitals are called hybrid
orbitals. and the phenomenon is called hybridisation.
Now after considering s–p hybridisation in BeCl2
p–sp sp–p
Cl ——— Be ———— Cl
bond strength of both the bonds will be equal.
Characteristic of Hybridisation :
(a) Hybridisation is a mixing of orbitals and not electrons. Therefore in hybridisation full filled, half filled and
empty orbitals may take part.
(b) Number of the hybrid orbitals formed is always be equivalent to number of atomic orbital which have
taken part in the process of hybridisation.
(c) Each hybrid orbital having two lobes, one is larger and other is smaller. Bond will be formed from large lobe.
(d) The number of hybrid orbitals on central atom of a molecule or ion = number of bonds + lone pair of
electron.
(e) One element can represent many hybridisation state depending on experimental conditions
E x . C showing sp, sp2 and sp3 hybridisation in its compounds.
(f) Hybrid orbitals are differentiated as sp, sp2, sp3 etc.
(g) The directional properties in hybrid orbital is more than atomic orbitals. Therefore hybrid orbitals form
stronger sigma bond. The directional property of different hybrid orbitals will be in following order.
sp < sp2 < sp3 < sp3d < sp3d2 < sp3d3
(h) Hybridize orbitals show oxial overlapping & form bond
TYPES OF HYBRIDISATION :
1. sp hybridisation :
(a) In this hybridisation one s– & one p– orbital of an atom are mixed to give two new hybrid orbitals which
are equivalent in shape & energy known as sp hybrid orbitals.
(b) These two sp hybrid orbitals are arrange in straight line & at bond angle 180°.
(c) s-character 50%
2s 2p
Be (ground state)
2s 2p
Be (excited state)
sp hybridisation
Be atom share two electrons sp sp
with F in BeF2,
F F
2. sp 2 Hybridisation :
(a) In this hybridisation one s & two p orbitals are mixed to give three new sp2 hybrid orbitals which all are in
same shape & equivalent energies.
(b) These three sp2 hybrid orbitals are at angle of 120° & giving trigonal planar shape.
(c) s-character 33.33% in each orbital.
2s 2p
B (ground state)
B (excited state)
sp2 hybrid orbitals
2 2 2
sp sp sp
B atom share 3 electrons
with 3 F atoms in BF3
F F F
3. sp 3 Hybridisation :
(a) In this hybridisation one s orbital & three p orbitals of an atom of a molecule or ion, are mixed to give four
new hybrid orbitals called as sp3 hybrid orbitals.
(b) The angle between these four hybrid orbitals will be 109° 28'
2s 2p
C (ground state)
C (excited state)
sp3 hybridisation
C atom share sp3 sp3 sp3 sp3
four electrons with H H H H
4 hydrogen atoms
(c) The shape obtained from these hybrid orbitals would be tetrahedron.
4. sp 3 d Hybridisation :
(a) In this hybridisation one s orbital, three p orbitals and one d orbital are mixed to give five new hybrid
orbitals which are equivalent in shape and energy called as sp3d hybrid orbitals.
(b) Out of these five hybrid orbitals, three hybrid orbitals are at 120° angle and two hybrid orbitals are
perpendicular to the plane of three hybrid orbitals that is trigonal planar, the shape of molecule becomes is
trigonal bipyramidal.
For example, PCl5 showing sp3d hybridisation
3s 3p 3d
P (ground state)
3s 3p 3d Cl
P* (excited state)
Cl P Cl
sp3d hybridisation
3 3 3 3 3
Cl
sp dsp dsp dsp dsp d
P atom share five e with Cl
Cl Cl Cl Cl Cl Cl
Structure of PCl5
(c) In this hybridisation dz2 orbital is hybridised with s and p orbitals.
In this way five sp3d hybrid orbitals form five sigma bond with five Cl atoms and give a molecule of PCl5,
shape of this molecule is trigonal bipyramidal.
Axial two P–Cl bonds are longer than equatorial three P–Cl bond due to repulsion
between 3 equitorial b.p. of e– and 2 axial b.p. of e–
5. sp 3 d 2 Hybridisation :
(a) In this hybridisation, one s-orbital, three p-orbitals & two d-orbitals are mixed to give six new hybrid
orbitals known as sp3d2 hybrid orbitals.
(b) The shape of molecule obtained from above six hybrid orbitals will be symmetrical octahedral.
(c) The angle between all hybrid orbitals will be 90°.
Ex. SF6, AlF6–3, PF6–, ICl5, XeF4, XeOF4, ICl4–,
(d) Two 'd' orbital participates in the hybridisation are dx2–y2 and dz2.
3s 3p 3d
SF6 S (ground state)
3s 3p 3d
S (IInd excited state)
sp3d2 hybridisation
3 2 3 2
sp3d2 sp3d2 sp3d2 sp3d2 sp d sp d
S (after hybridisation) share 6e– with 6 F atoms
F F F F F F
6. sp 3 d 3 Hybridisation :
(a) In this hybridisation, one s-orbital, three p-orbitals & three d-orbitals are mixed to give seven new hybrid
orbitals known as sp3d3 hybrid orbitals.
(b) In this hybridisation d-orbitals used are dxy, d x2 y 2 & d z 2 orbitals.
(c) These seven sp3d3 orbitals are configurated in pentagonal bipyramidal shape.
(d) Five bond angles are of 72° & ten bond angles of 90°.
(e) The following examples showing sp3d3 hybridisation –IF7 & XeF6.
F F
F F
I
F F
F
