Brief intro of Hybridisation and explaniation of hybridisation in d orbital with examples of inorganic complesex

1. What is hybridization?
• Hybridisation is the process of intermixing of orbitals with slightly different energies so as to
redistribute their energies forming new orbitals having equal energies and shapes
• But why was the concept of hybridization created?
4
9Be 1s2 2s2 2p0
5
10B 1s2 2s2 2p1
6
12C 1s2 2s2 2p2
If we look at the electronic configuration of Be, B and C. Then according to octet rule Be should behave as Nobel gas,
B should show univalency and carbon show bi valency.
Yet It is very well known that Be shows bivalency making compounds like BeF
2
and B shows trivalancey making
compounds like BF
3
, C shows tetravalency making millions compounds.
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2. • To explain this anomaly Pauling formulated the theory of Hybridisation.
• Whenever electrons are excited they move from lower energy state to higher energy state i.e. they move from lower
orbital to next permissible orbital.
1s 2s 2p 1s 2s 2p
Be(Ground state) B (Ground state )
Be(Excited state) B (Excited state)
1s 2s 2p
C(Ground state)
C (Excited state)
• We Know that S and P orbitals have different energies and radii so the bonds formed will also be of different strength, but
experimentally it was found that all bonds in formed by Be, B and C after excited electrons are equal in strength.
• This is where hybridisations comes to rescue. According to hybridization S and P orbital combine to give new orbitals with
equivalent energies and shapes.
• S,P and their hybridised variants are as follows.
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3. • Expanded Octet
• Elements beyond third period of periodic table have 3d orbitals, apart from 3s and 3p.These 3b orbitals may be empty or
have electrons in them, but they are available for bonding, because of this a large number of elements have more than
eight electrons in there outer shell after bonding.
• These orbitals alongside with 3S and 3P orbitals intermix to give new hybrid orbitals like SP3d,sp3d2 and other orbitals
involving d orbital.
• sp3d hybridization
Formation of sp³d hybrid orbitals can be well understood by considering AB₅ type molecules. E.g. – PCl₅, PF₅, SbCl₅
• The bonding in PCl₅ may be described using hybrids of the 3s, 3p and 3d (3dz²) atomic orbitals of P All the five hybridized
orbitals are not equivalent.
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• Three of these are oriented towards the 3 corners of an equilateral triangle making an angle of 120° between them. The
bonds formed by these orbitals are called equatorial bonds. These 3 orbitals are planar.
• The remaining two orbitals are oriented at right angles to the plane of first set of 3 orbitals. The bonds formed by these
orbitals are called axial bonds .
• PCl₅ molecule has trigonal bipyramidal geometry.
• The bond angle between axial and equatorial bonds are of 90°and that of two axial hybrid orbitals is of 180o

5. • In trigonal bipyramidal geometry, the axial bonds are slightly longer than the equatorial bonds Axial bonds experience
greater repulsion from other bonds than the equatorial bonds
• For the bond pair of electrons of the axial P- Cl bond, there are 3 bond pair- bond pair repulsions whereas for the bond pair
of electrons of the equatorial P-Cl bond, there are only 2 bond pair-bond pair .
• repulsions.
• Thus in PCl₅ molecule, length of each P-Cl axial bond is 2.19A° while the length of each P-Cl equatorial bond is 2.04A°
• If the d-orbital involved in sp³d hybridization is the dx²-y²orbital the molecule (AB₅) formed would have a square pyramidal
geometry.
• This geometry is less stable than the trigonal bipyramidal geometry unless stabilized by some other factors such as greater
probability of pi bonding in the plane containing one A and four B atoms.
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6. • If the d-orbital involved in sp³d hybridization is the dx²-y²orbital the molecule (AB₅) formed would have a square pyramidal
geometry
• This geometry is less stable than the trigonal bipyramidal geometry unless stabilized by some other factors such as greater
probability of pi bonding in the plane containing one A and four B atoms
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7. SF₄ MOLECULE
• S(16)- 3s²3px²py¹pz¹.
• The molecule has an irregular tetrahedral geometry.
• The lone pair present in equatorial position would experience comparatively less repulsion and the molecule structure would
be stable.
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8. ClF₃ (Chlorine Trifluoride) molecule.
• Chlorine is the central atom.
• Cl (17)- 3s²3px²py²pz1
• In ClF₃, the central chlorine atom is surrounded by three bond pairs and two lone pairs of electrons
• On the basis of VSEPR theory the molecule is expected to be T-shaped
• Due to the presence of lone pairs, there is distortion in the structure
• ClF₃ has distorted T-shape with FClF bond angle 87.6°
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9. XeF₂ (Xenon difluoride) Molecule
• Xe(54)- 5s²5px²py²pz2.
• In XeF₂ molecule the central atom Xe is surrounded by five completely filled orbitals, two of which contain bond pairs of
electrons and the remaining three contain lone pairs of electrons.
• The three lone pairs are present in equatorial positions to minimize electron pair repulsions.
• Due to symmetrical arrangement of lone pairs around the central Xe atom, the molecule has linear structure.
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10. sp³d² Hybridization
SF6
S (16)- 3s²3px²py¹pz¹
• Six orbitals hybridize to form six sp³d² hybrid orbitals.
• The d-orbitals used are dx²-y² and dz² .
• The 6 hybrid orbitals are directed towards the 6 corner of a regular octahedron.
• Each of these six sp³d² hybrid orbitals overlaps with the half filled p-orbital of each fluorine atom to form SF₆ molecule.
• SF₆ molecule has an octahedral geometry.
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XeF₄(Xenon tetrafluoride) molecule
Xe(54)- 5s²5px²py²pz²
• The central atom Xe is surrounded by 6 fully filled hybrid orbitals .
• Four of these orbitals contain bond pairs while the remaining two contain lone pairs of electrons .

12. • The two orbitals containing lone pairs are present in axial positions, one above and the other below the plane of the 4
fluorine atoms .
• Lone pair orbitals in these positions cause minimum repulsion.
• The geometry of XeF₄ molecule is square planar.
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13. IF₅ (Iodine pentafluoride) molecule
• The central atom Iodine is surrounded by 6 completely filled hybrid orbitals.
• Five of which contain bond pairs and one contains a lone pair of electrons.
• IF₅ molecule geometry is square pyramidal.
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14. sp³d³ hybridization
E.g.- IF₇ I (53)- 5s²px²py²pz¹
• Seven orbitals (5s, 5px, 5py, 5pz, 5dxy, 5dyz and 5dxz) hybridize to give seven sp³d³ hybrid orbitals
• Each of these hybrid orbitals overlaps with the half-filled 2p orbitals of each fluorine atom to form IF₇ molecule
• The resulting molecule acquires pentagonal bipyramidal geometry
• In this molecule, all the seven bonds are not equivalent. Five of these are directed towards the vertices of a regular
pentagon making an angle of 72° with one another
• The remaining two are oriented at right angles to the plane of the first set of five orbitals. Thus the bond angles in this
molecule are of 72° and 90°
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For atoms with n > 3, d and f orbitals become important in case of transition metal complexes.
• One nd, one (n+1) s and two (n+1) p orbitals may combine to form four dsp² hybrid orbitals lying in a plane and
directed towards the 4 corners of a square in the xy-plane.
The set of four dsp² hybrids may be given as
Ψ₁ =
1
2
s + 1√2px+
1
2
dxy
Ψ₂ =
1
2
s -1√2px+
1
2
dxy
Ψ₃=
1
2
s + 1√2py-
1
2
dxy
Ψ₄=
1
2
s -1√2py-
1
2
dxy
Another type of hybridization is known in which two nd, one (n+1) s and three (n+1) p orbitals combine to form six
d²sp³ hybrid orbitals directed towards the six corners of an octahedron.

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These are given as
Ψ₁ =
1
√6
s +
1
√2
pz+
1
√3
dz²
Ψ₂=
1
√6
s -
1
√2
pz+
1
√3
dz²
Ψ₃=
1
√6
s +
1
√2
px+
1
√12
dz² +
1
2
dx²-y²
Ψ₄=
1
√6
s -
1
√2
px+
1
√12
dz² +
1
2
dx²-y²
Ψ₅=
1
√6
s +
1
√2
py+
1
√12
dz² -
1
2
dx²-y²
Ψ₆=
1
√6
s -
1
√2
py+
1
√12
dz² -
1
2
dx²-y²
They form still stronger bonds.
Examples of which are to be found in 6-coordinated complexes of transition metals.

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