Hybridisation: Definition, Formula, Examples, Questions, C2, BF3, Water

Hybridization in chemistry means mixing atomic orbitals to recombine into a new set of hybrid orbitals. This is necessary for investigating reasons relating to the shapes and bonding properties of molecules. Brought forth by Linus Pauling, this concept of hybridization explained the geometry of molecules in a much easier and more intuitive way than before. Types of hybridization include sp, sp², sp³, sp³d, and sp³d²—these hybridizations correspond to different molecular geometries and bonding patterns. For instance, the sp³ hybridization gives a tetrahedral geometry, typical for molecules like methane, and CH₄, while the hybridization of sp² forms provides a trigonal planar geometry, seen for ethene, C²H⁴. Hybrid orbitals are formed by mixing the s- and p- orbitals of an atom (and sometimes the d orbitals). The result is that orbitals become degenerate (of the same energy) and alike in shape. It forms a basis necessary for structure and reactivity predictions and explanations of organic compounds and complex inorganic molecules. Hybridization is descriptive of the three-dimensional structure of molecules and electron distribution within the different chemical bonds. It, therefore, rationalizes the three-dimensional structure of molecules and electron distribution within the various chemical bonds.

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This Story also Contains

1. The salient features and conditions for hybridization:
2. Types of Hybridisation
3. How to find Hybridisation
4. sp Hybridization
5. sp2 Hybridization
6. sp3 Hybridization
7. sp3d Hybridisation
8. sp3d2 Hybridization
9. d2sp3 hybridisation
10. sp3d3 hybridization
11. Some Solved Examples
12. Summary

When atoms are bound together in a molecule, the individual atomic orbitals combine to produce new forms of orbitals that are the same in energy and have the same size and shape. This process of combining atomic orbitals is called hybridization and is mathematically accomplished by the linear combination of atomic orbitals, LCAO. The new orbitals that result are called hybrid orbitals.

For example, the valence orbitals in an isolated oxygen atom are a 2s orbital and three 2p orbitals. However, the valence orbitals in an oxygen atom in a water molecule differ; they consist of four equivalent hybrid orbitals that point approximately toward the corners of a tetrahedron as shown in the figure given below. Consequently, the overlap of the O and H orbitals should result in a tetrahedral bond angle (109.5°) but the real bond angle in a water molecule is 104.5°, this is because of the presence of the lone pairs of electrons in two of the hybrid orbitals.

The salient features and conditions for hybridization:

1. Hybrid orbitals do not exist in isolated atoms. They are formed only in covalently bonded atoms.

2. Hybrid orbitals have shapes and orientations that are very different from those of the atomic orbitals in isolated atoms.

3. A set of hybrid orbitals is generated by combining atomic orbitals. The number of hybrid orbitals in a set is equal to the number of atomic orbitals that were combined to produce the set.

4. All orbitals in a set of hybrid orbitals are equivalent in shape and energy.

5. The type of hybrid orbitals formed in a bonded atom depends on its electron-pair geometry as predicted by the VSEPR theory.

6. Hybrid orbitals overlap to form σ bonds. Unhybridized orbitals overlap to form π bonds.

Types of Hybridisation

The hybridization can be of several types depending on the number of hybrid orbitals involved in the formation of molecules. The table given below describes all types of hybridization and their geometries.

How to find Hybridisation

The hybridization depends upon sigma bonds and a lone pair of electrons.

Thus,

Hybridization = Number of sigma bonds + Number of lone pairs present on the central atom

For example, hybridization for NH₃ is sp³ and its molecular geometry is tetrahedral.

NH₃ has 3 sigma bonds and 1 lone pair, thus hybridization for NH₃:

3 sigma bonds + 1 lone pair = 4

Thus hybridization for NH₃ is sp³ and its geometry is tetrahedral.

sp Hybridization

This hybridization process involves mixing of the valence s orbital with one of the valence p orbitals to yield two equivalent sp hybrid orbitals that are oriented in a linear geometry as shown in the figure. The number of atomic orbitals combined always equals the number of hybrid orbitals formed. The p orbital is one orbital that can hold up to two electrons. The sp set is two equivalent orbitals that point 180^oC from each other. The two electrons that were originally in the s orbital are now distributed to the two sp orbitals, which are half filled.

sp² Hybridization

When 1 s-orbital and 2 p-orbitals are involved in the molecule formation then the equivalent set of orbitals are known as sp² hybrid orbitals. These hybrid orbitals arrange themselves at an angle of 120^oC as shown in the figure.

sp³ Hybridization

When 1 s-orbital and 3 p-orbitals are involved in the molecule formation then the equivalent set of orbitals are known as sp³ hybrid orbitals. The bond angle between these hybrid orbitals is 109^oC as shown in the figure.

sp³d Hybridisation

When 1 s-orbital, 3 p-orbitals, and 1 d-orbital are involved in the molecule formation then the equivalent set of orbitals are known as sp³d hybrid orbitals. There are two kinds of bonds formed for sp³d hybridization, i.e., 2 axial bonds and 3 equatorial bonds. The angle between the axial bond and the equatorial plane is 90^oC while the bond angle between the equatorial bonds is 120^oC as shown in the figure given below:

sp³d² Hybridization

When 1 s-orbital, 3 p-orbitals and 2 d-orbitals are involved in the molecule formation then the equivalent set of orbitals are known as sp³d² hybrid orbitals. There are two kinds of bonds formed for sp³d² hybridisation, i.e., 2 axial bonds and 4 equatorial bonds. The angle between the axial bond and the equatorial plane is 90^oC while the bond angle between the equatorial bonds is 90^oC as shown in the figure given below:

d²sp³ hybridisation

When 2 d-orbital, 1 s-orbital and 3 p-orbitals are involved in the molecule formation then the equivalent set of orbitals are known as d²sp³ hybrid orbitals. There are two kinds of bonds formed for sp³d² hybridisation, i.e, 2 axial bonds and 4 equatorial bonds. The angle between the axial bond and the equatorial plane is 90^oC while the bond angle between the equatorial bonds is 90^oC as shown in the figure given below:

sp³d³ hybridization

When 1 s-orbital, 3 p-orbitals and 3 d-orbitals are involved in molecule formation then the equivalent set of orbitals are known as sp³d³ hybrid orbitals. The sp³d³ hybridization has a pentagonal bipyramidal geometry i.e., five bonds in a plane, one bond above the plane and one below it.

Recommended topic video on(Hybridisation)

Some Solved Examples

Example 1: The type of hybridization and number of lone pair (s) of electrons of Xe in XeOF₄ respectively, are :

1) $s p^3 d^2$ and 1
2) $s p^3 d$ and 2
3) $s p^3 d^2$ and 2
4) $s p^3 d$ and 1

Solution

As we have learned in Hybridisation:

Hybridisation is $\mathrm{sp}^3 \mathrm{~d}^2$
It contains $5 \sigma$ bond and $1 \pi$ bond.
It has 1 lone pair of electrons.

Hence, the correct answer is Option (1)

Example 2: The correct statement about $I C l_5$ and $I C l_4^{-}$is:
1)Both are isostructural
2) $\mathrm{ICl}_5$ is trigonal bipyramidal and $\mathrm{ICl}_4^{-}$is tetrahedral
3) $I C l_5$ is square bipyramidal and $I C l_4^{-}$is tetrahedral
4) $I C l_5$ is square pyramidal and $I C l_4^{-}$is square planar.

Solution
$I C l_5$ is square bipyramidal and $\mathrm{Cl}_4^{-}$is square planar.
$I C l_5:-$

Square Pyramidal

Lone Pair =1

Bond Pair=5

hybridisation= sp³d²

ICl₄^- :-

Square planar

Lone Pairs = 2

Bond Pairs = 4

hybridisation = sp³d²

Hence, the correct answer is Option (4)

Example 3: The orbitals undergoing Hybridisation involve

1) Orbitals of the same atom with almost similar energies

2)Orbitals of different atoms but with equal energies

3)Orbitals of different atoms with different energies

4)Orbitals of the same atoms with exactly equal energies

Solution

The orbitals of the same atom having similar energies undergo hybridization to form hybrid orbitals which have the same energy.

Hence, the answer is the option (1).

Example 4: In which pair of species, both species do have a similar geometry?

1)CO₂, SO₂

2)CO₂^3- and SO₃²⁻

3) SO₄^2- and ClO₄^-

4)PH₃ and BH₃

Solution

The geometry of CO₂ is linear.(O=C=O)(O=C=O)

The geometry of SO₂ is v-shape

The geometry of CO₃^2- is trigonal planar.

The geometry of SO₃²⁻ is a pyramidal shape

The geometry of SO₄²⁻ is tetrahedral

The geometry of ClO₄⁻ is tetrahedral

The geometry of NH₃ is a pyramidal shape

The geometry of BH₃ is trigonal planar

Hence, the answer is the option (3).

Summary

Hybridization is a concept in chemistry that describes mixing atomic orbitals to form hybrid orbitals, which allows for the determination of the shape and bonding properties of molecules. It was introduced by Linus Pauling, and it includes types such as sp, sp², sp³, sp³d, and sp³d²—each being associated with specific molecular geometries. For example, sp3 hybridization would give a tetrahedral shape and sp2 results in a trigonal planar structure. In forming hybrid orbitals, the 's' and 'p' orbitals of an atom combine, and sometimes the 'd' orbitals, thereby forming orbitals that become equal in energy and shape. This, therefore, is a process of central importance in understanding the structure and reactivity of organic and inorganic molecules. Through hybridization, a chemist would be able to predict, explain, and model three-dimensional atomic arrangement in a molecule and electron distribution within bonds. Such understanding is cardinal in studying chemical reactions, molecular interactions, and the general behavior of substances at the atomic level.