Hybridization

Hybridization, in Chemistry, is defined as the concept of mixing two atomic orbitals to give rise to a new type of hybridized orbitals. This intermixing usually results in the formation of hybrid orbitals having entirely different energy, shapes, etc. The atomic orbitals of the same energy level mainly take part in hybridization. However, both fully-filled and half-filled orbitals can also take part in this process, provided they have equal energy.

On the other hand, we can say that the concept of hybridization is an extension of the valence bond theory, and it helps us to understand the formation of bonds, bond energies and bond lengths.

Table of Contents

• Key Features
• Types
• sp Hybridization
• sp² Hybridization
• sp³ Hybridization
• sp³d Hybridization
• sp³d2 Hybridization
• FAQs

What Is Hybridization?

Redistribution of the energy of orbitals of individual atoms to give orbitals of equivalent energy happens when two atomic orbitals combine to form a hybrid orbital in a molecule. This process is called hybridization.  During the process of hybridization, the atomic orbitals of comparable energies are mixed together and mostly involves the merging of two ‘s’ orbitals or two ‘p’ orbitals or the mixing of an ‘s’ orbital with a ‘p’ orbital, as well as ‘s’ orbital with a ‘d’ orbital. The new orbitals, thus formed, are known as hybrid orbitals. More significantly, hybrid orbitals are quite useful in explaining atomic bonding properties and molecular geometry.

Let us have a quick look at the example of a carbon atom. This atom forms 4 single bonds wherein the valence-shell s orbital mixes with 3 valence-shell p orbitals. This combination leads to the formation of 4 equivalent sp³ mixtures. They will have a tetrahedral arrangement around the carbon, which is bonded to 4 different atoms.

Hybridization Video Lesson

⇒ Also Read

• Chemical Bonding
• Molecular Orbital Theory

Key Features of Hybridization

• Atomic orbitals with equal energies undergo hybridization.
• The number of hybrid orbitals formed is equal to the number of atomic orbitals mixed.
• It is not necessary that all the half-filled orbitals must participate in hybridization. Even completely filled orbitals with slightly different energies can also participate.
• Hybridization happens only during the bond formation and not in an isolated gaseous atom.
• The shape of the molecule can be predicted if the hybridization of the molecule is known.
• The bigger lobe of the hybrid orbital always has a positive sign, while the smaller lobe on the opposite side has a negative sign.

Try this: Give the hybridization states of each of the carbon atoms in the given molecule.

• H₂C = CH – CN
• HC ≡ C − C ≡ CH
• H₂C = C = C = CH₂

Types of Hybridization

Based on the types of orbitals involved in mixing, the hybridization can be classified as sp³, sp², sp, sp³d, sp³d² and sp³d³. Let us now discuss the various types of hybridization, along with their examples.

sp Hybridization

sp hybridization is observed when one s and one p orbital in the same main shell of an atom mix to form two new equivalent orbitals. The new orbitals formed are called sp hybridized orbitals. It forms linear molecules with an angle of 180°.

• This type of hybridization involves the mixing of one ‘s’ orbital and one ‘p’ orbital of equal energy to give a new hybrid orbital known as an sp hybridized orbital.
• The sp hybridization is also called diagonal hybridization.
• Each sp hybridized orbital has an equal amount of s and p characters – 50% s and 50% p characters.

Examples of sp Hybridization:

• All compounds of beryllium, like BeF₂, BeH_2, BeCl₂
• All compounds of a carbon-containing triple bond, like C₂H₂.

sp² Hybridization

sp² hybridization is observed when one s and two p orbitals of the same shell of an atom mix to form 3 equivalent orbitals. The new orbitals formed are called sp² hybrid orbitals. 

• sp² hybridization is also called trigonal hybridization.
• It involves the mixing of one ‘s’ orbital and two ‘p’ orbitals of equal energy to give a new hybrid orbital known as sp².
• A mixture of s and p orbital formed in trigonal symmetry and is maintained at 120⁰.
• All three hybrid orbitals remain in one plane and make an angle of 120° with one another. Each of the hybrid orbitals formed has a 33.33% ‘s’ character and 66.66% ‘p’ character.
• The molecules in which the central atom is linked to 3 atoms and is sp2 hybridized have a triangular planar shape.

Examples of sp² Hybridization

• All the compounds of Boron, i.e., BF_{3 and} BH₃
• All the compounds of carbon, containing a carbon-carbon double bond, Ethylene (C₂H₄)

sp³ Hybridization

When one ‘s’ orbital and 3 ‘p’ orbitals belonging to the same shell of an atom mix together to form four new equivalent orbitals, the type of hybridization is called a tetrahedral hybridization or sp³. The new orbitals formed are called sp³ hybrid orbitals.

• These are directed towards the four corners of a regular tetrahedron and make an angle of 109°28’ with one another.
• The angle between the sp3 hybrid orbitals is 109.28⁰
• Each sp³ hybrid orbital has 25% s character and 75% p character.
• Examples of sp³ hybridization are ethane (C₂H₆) and methane.

sp³d Hybridization

sp³d hybridization involves the mixing of 1s orbital, 3p orbitals and 1d orbital to form 5 sp³d hybridized orbitals of equal energy. They have trigonal bipyramidal geometry.

• The mixture of s, p and d orbital forms trigonal bipyramidal symmetry.
• Three hybrid orbitals lie in the horizontal plane inclined at an angle of 120° to each other, known as the equatorial orbitals.
• The remaining two orbitals lie in the vertical plane at 90 degrees plane of the equatorial orbitals, known as axial orbitals.
• Example: Hybridization in phosphorus pentachloride (PCl₅)

sp³d² Hybridization

• sp³d² hybridization has 1s, 3p and 2d orbitals, that undergo intermixing to form 6 identical sp³d² hybrid orbitals.
• These 6 orbitals are directed towards the corners of an octahedron.
• They are inclined at an angle of 90 degrees to one another.