Hybridization and Exceptions of Hybridization
Hybridization
The process of mixing of two or more different atomic orbitals having almost same energy to form equal number of equivalent orbitals called hybrid orbitals and the phenomenon is called hybridization.
Hybrid orbitals are different from atomic orbitals and they are directional so they have definite geometrical shape.
Hybridization is hypothetical so it is not possible for every molecules. Hybridization is essential for understanding chemical bonding and predicting the molecular geometry of compounds. It explains why molecules have specific shapes and determines their physical and chemical properties.
Types of Hybridization
Hybridization is of different types some of them are discussed here-
sp Hybridisation
Mixing of one 's' with one 'p' orbitals of almost equal energy to give two identical and degenerate 'sp' hybrid orbitals. These two hybrid orbitals arranged linearly in 3D space. The bond angle is 180o and they possess 50% 's' and 50% 'p' character.
sp2 Hybridisation
Mixing of one 's' with two 'p' orbitals of almost equal energy to give three identical and degenerate sp2 hybrid orbitals. These three hybrid orbitals arranged in 3D space as triangular planar. The bond angle is 120o and they possess 33.3% 's' and 66.6% 'p' character.
sp3 Hybridisation
Mixing of one 's' with three 'p' orbitals of almost equal energy to give four identical and degenerate sp3 hybrid orbitals. These four hybrid orbitals arranged tetrahedrally in 3D space. The bond angle is 109.5o and they possess 25% 's' and 75% 'p' character.
sp3d Hybridisation
Mixing of one 's' with three 'p' and one d orbitals of almost equal energy to give five identical and degenerate sp3d hybrid orbitals. These five hybrid orbitals arranged in 3D space as triangular bipyramidal. The bond angle are 120o and 90o and they possess 20% 's' and 60% 'p' and 20% d character.
sp3d2 Hybridisation
Mixing of one 's' with three 'p' and two d orbitals of almost equal energy to give six identical and degenerate sp3d2 hybrid orbitals. These six hybrid orbitals arranged in 3D space as octahedral. The bond angle is 90o and they possess 16.6% 's' and 49.8% 'p' and 33.2% d character.
sp3d3 Hybridisation
Mixing of one 's' with three 'p' and three d orbitals of almost equal energy to give seven identical and degenerate sp3d3 hybrid orbitals. These seven hybrid orbitals arranged in 3D space as pentagonal bipyramidal. The bond angle is 72o and they possess 14.14% 's' and 42.42% 'p' and 42.42% d character.
Determination of Hybridization
Short Formula
H = 1/2(V + M - C + A)
V= No. of valence electrons of central atom
M- No. Of monovalent atom
C- Total Cation charge
A- Total Anion charge
Example
CH4
Central atom carbon valence electron (V) = 4
No. of monovalent atom (hydrogen) (M) = 4
In CH4, there is no chage. So, C and A is zero.
Therefore, H = 1/2(4 + 4) = 4
The value of 4 indicates the hybridization of CH4 is sp3.
Other Method
This method involves a number of steps-
1. Calculate the total valence electron (TVE) of the given molecule
2. Calculate the duet/octet electrons
3. Calculate the lone pair electrons in the molecule
4. No. of hybrid orbitals need for bonding (= no. of bonded atoms + no. of L.P.)
5. Calculate the no. of hybrid orbitals
6. Hybridization- According to value of step 5
7. Structure- According to hybridization
8. Shape- if molecules does not have lone pair(s), then structure and shape are same however, if molecules have lone pair(s), then structure and shape are different.
Example
CH4
TVE = 4 + (1 x 4) = 8
No. of duet electrons = 4 x 2 = 8
No. of Lone Pair = 1/2(8 - 8) = 0
No. of hybrid orbitals need for bonding = 4 + 0 = 4
No. of hybrid orbitals = 4
Hybridization = sp3
Structure = Tetrahedral
Shape = Tetrahedral (as there is no lone pair)
Correct hybridization of P in PH3 molecule
a. sp3
b. sp2
c. sp2d
d. None of the above
Hybridization of Mn in KMnO4 molecule
a. sp3
b. sd3
c. sp2d
d. None of the above
Hybridization of Cr in K2Cr2O7 molecule
a. sp3
b. sd3
c. sp2d
d. None of the above
Exceptions of Hybridization
Several exceptions of hybridiation has been noted. Some of them are discussed below-
Hybridization of Boron Trifluoride (BF3)
According to hybridization theory, BF3 is sp2 hybridized and structure or shape is trigonal planar but in actual, BF3 is trigonal pyramidal shape suggesting that BF3 is sp3 hybridized. This is due to the empty p orbital on boron, which can accept electrons from the fluorine atoms, leading to the formation of a three-center, two-electron bond.
Hybridization of Iodide Pentafluoride (IF5)
According to hybridization theory, hybridization of IF5 is sp3d2 and structure or shape is pentagonal bipyramidal but IF5 exhibits a square pyramidal shape, indicating sp3d hybridization. This is due to the large size and low electronegativity of iodine, which allows for the expansion of the valence shell to accommodate the additional d orbital.
Hybridization of Xenon Tetrafluoride (XeF4)
According to hybridization theory, XeF4 is sp3d hybridized and structure or shape is square planar but XeF4 exhibits a distorted tetrahedral shape due to the relatively large size and polarizability of xenon, which results in the distortion of the molecular geometry.
Hybridization of Ozone (O3)
According to hybridization theory, ozone is sp2 hybridied and is linear in shape but in actual ozone has a bent shape, with a bond angle of approximately 116°. This is explained by the resonance between the two resonanting structures of ozone, which leads to the partial double bond character in the central O-O bond.
Hybridization of CO3−2 and SO4−2
According to hybridization theory, these ions are sp3 hybridized, resulting in a tetrahedral shape. However, these ions exhibit a trigonal planar shape, with a bond angle of approximately 120°. This is due to the presence of multiple resonance structures, which result in the delocalization of electrons and the equalization of bond lengths.
Hybridization of KMnO4 and K2Cr2O7
According to hybridization theory, KMnO4 and K2Cr2O7 is sp3 hybridized but actual hybridization is d3s because in sp3 the gap between 4s and 4p orbital energy is large so mixing not preffered but in d3s the gap between 3d and 4s is small so mixing preffered and hybridisation becomes d3s.
Hybridization of PH3
According to hybridization theory, PH3 is sp3 hybridized. However, the PH3 molecule does not have any hybridisation because PH3 is a Drago molecule. PH3 has no hybridisation because it makes all of its connections with its purest p orbitals.
Factors Contributing to Exceptions
Exceptions to hybridization theory typically arise due to the following factors-
1. The presence of empty or partially filled d orbitals
2. Large or polarizable atoms
3. Resonance or delocalization of electrons
4. Steric effects
