Hybridisation of Orbitals: Concept, Types, and Applications

 🌐 Hybridisation of Orbitals: Concept, Types, and Applications

🔹 Introduction

In chemistry, understanding how atoms bond with each other is essential to explain the structure and properties of molecules. One of the most important concepts that helps us in this explanation is Hybridisation of Orbitals.

The concept was introduced by Linus Pauling in 1931 to explain the equivalent bond formation in molecules like methane (CH₄). Hybridisation is not just a theoretical idea—it is widely used in explaining molecular geometry, bond strength, and bond angles.

In this article, we will explore:

What hybridisation means.

The theory behind orbital mixing.

Different types of hybridisation (sp, sp², sp³, sp³d, sp³d², sp³d³).

Examples and geometries.

Applications in daily life and advanced chemistry

🔹 What is Hybridisation?

Definition:

Hybridisation is the process of mixing atomic orbitals of similar energy levels to form new orbitals, called hybrid orbitals, which are equivalent in shape and energy.

These hybrid orbitals then overlap with orbitals of other atoms to form stable chemical bonds.

Key Features of Hybridisation:

1. Only orbitals of similar energy mix together.

2. The number of hybrid orbitals formed = number of atomic orbitals mixed.

3. Hybrid orbitals have a definite geometry, which determines the shape of molecules.

4. Hybridisation explains why equivalent bonds (like four C–H bonds in CH₄) exist.

🔹 Conditions for Hybridisation

Orbitals should have comparable energy (e.g., 2s and 2p).

Orbitals must belong to the same atom.

Hybridisation occurs during bond formation, not in isolated atoms.

Both half-filled and fully filled orbitals may participate.

🔹 Types of Hybridisation

Hybridisation depends on the number of orbitals involved. Below are the main types with geometries and examples:

1. sp Hybridisation

Mixing: 1 s + 1 p orbital → 2 sp orbitals.

Geometry: Linear (180° bond angle).

Examples: BeCl₂, CO₂, C₂H₂ (acetylene).

👉 Explanation: In BeCl₂, the central atom beryllium has two sp hybrid orbitals oriented linearly, forming σ bonds with chlorine atoms.

2. sp² Hybridisation

Mixing: 1 s + 2 p orbitals → 3 sp² orbitals.

Geometry: Trigonal Planar (120° bond angle).

Examples: BF₃, C₂H₄ (ethene), SO₃.

👉 Explanation: In BF₃, boron forms three equivalent sp² orbitals arranged in a plane at 120°, bonding with fluorine.

3. sp³ Hybridisation

Mixing: 1 s + 3 p orbitals → 4 sp³ orbitals.

Geometry: Tetrahedral (109.5° bond angle).

Examples: CH₄ (methane), NH₃ (trigonal pyramidal), H₂O (bent shape).

👉 Explanation: In methane, carbon undergoes sp³ hybridisation, giving rise to four identical tetrahedral bonds with hydrogen.

4. sp³d Hybridisation

Mixing: 1 s + 3 p + 1 d orbital → 5 sp³d orbitals.

Geometry: Trigonal Bipyramidal.

Bond Angles: 120° (equatorial), 90° (axial).

Examples: PCl₅, SF₄.

5. sp³d² Hybridisation

Mixing: 1 s + 3 p + 2 d orbitals → 6 sp³d² orbitals.

Geometry: Octahedral (90° bond angle).

Examples: SF₆, [Co(NH₃)₆]³⁺.

6. sp³d³ Hybridisation

Mixing: 1 s + 3 p + 3 d orbitals → 7 sp³d³ orbitals.

Geometry: Pentagonal Bipyramidal.

Examples: IF₇.

🔹 Table of Hybridisation, Geometry, and Examples

Type of Hybridisation Orbitals Involved Geometry Bond Angle Examples

sp 1s + 1p Linear 180° BeCl₂, CO₂

sp² 1s + 2p Trigonal Planar 120° BF₃, C₂H₄

sp³ 1s + 3p Tetrahedral 109.5° CH₄, NH₃, H₂O

sp³d 1s + 3p + 1d Trigonal Bipyramidal 120°/90° PCl₅, SF₄

sp³d² 1s + 3p + 2d Octahedral 90° SF₆, XeF₄

sp³d³ 1s + 3p + 3d Pentagonal Bipyramidal 72°/90° IF₇

🔹 Difference Between Hybrid Orbitals and Atomic Orbitals

Property Atomic Orbitals Hybrid Orbitals

Shape s – spherical, p – dumbbell Same shape in a set

Energy Different for s, p, d Equal energy (degenerate)

Orientation Random Definite geometry

Formation Natural Formed during bond making

🔹 Applications of Hybridisation

1. Explains Molecular Geometry – Why methane is tetrahedral, ethene is planar, and acetylene is linear.

2. Bond Strength & Stability – Hybrid orbitals give stronger σ bonds than pure orbitals.

3. Valence Bond Theory (VBT) – Hybridisation supports VBT in explaining chemical bonding.

4. Transition Metal Complexes – Explains geometry in coordination compounds (octahedral, square planar).

5. Organic Chemistry – Essential in explaining structures of alkanes, alkenes, alkynes, and aromatic compounds.

6. Material Science – Helps understand bonding in diamond (sp³) and graphite (sp²).

🔹 Hybridisation in Real Life Examples

Diamond → Each carbon is sp³ hybridised (tetrahedral, hardest structure).

Graphite → Each carbon is sp² hybridised, with delocalised electrons (good conductor).

Acetylene (C₂H₂) → sp hybridisation, explaining linear shape and triple bonds.

Ammonia (NH₃) → sp³ hybridisation with lone pair, giving trigonal pyramidal shape.

🔹 Hybridisation and Bond Character

The percentage of s-character in hybrid orbitals influences bond properties:

sp (50% s + 50% p) → Shortest and strongest bonds.

sp² (33% s + 67% p) → Intermediate bond strength.

sp³ (25% s + 75% p) → Longest and weakest bonds among these three.

👉 This explains why C≡C bonds are stronger than C=C or C–C bonds.

🔹 Common Misconceptions in Hybridisation

1. Hybridisation is not a physical mixing of orbitals; it’s a mathematical concept.

2. Not all molecules follow hybridisation rules perfectly (e.g., some d-orbital participation is debated).

3. Lone pairs also occupy hybrid orbitals, influencing shape.

🔹 Conclusion

Hybridisation is a cornerstone in understanding chemical bonding and molecular structures. It explains why bonds are equivalent, why molecules adopt specific geometries, and how bond strength varies. From the hardness of diamond to the conductivity of graphite, hybridisation provides a simple yet powerful explanation of chemical behavior.

As chemistry advances into nanotechnology, materials science, and drug design, hybridisation remains a fundamental concept bridging atomic theory and molecular properties.