Hybridisation - Practice Questions & MCQ

When atoms are bound together in a molecule, the individual atomic orbitals combine to produce new forms of orbitals that are same in energy and have same size and shape. This process of combining of 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. But 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 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 hybridisation 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 hybridisation and their geometries.

How to find Hybridisation

The hybridisation depends upon sigma bonds and lone pair of electrons. 

Thus, 

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

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

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

3 sigma bonds + 1 lone pair = 4

Thus hybridisation 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° 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 1200 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 1090 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 hybridisation, i.e, 2 axial bonds and 3 equatorial bonds. The angle between the axial bond and the equatorial plane is 900 while the bond angle between the equatorial bonds is 1200 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 900 while the bond angle between the equatorial bonds is 900 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 900 while the bond angle between the equatorial bonds is 900 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.