Hybridisation

1.What is Hybridisation?

• Hybridisation is the mixing of atomic orbitals of similar energy (like s, p, d) to form new equivalent orbitals called hybrid orbitals.
• This concept was introduced by Linus Pauling to explain molecular shapes

2.Why is Hybridisation Needed?

Without hybridisation:

• Orbitals have different shapes and energies

• Bond angles and molecular geometry cannot be explained properly

 Hybridisation helps explain:

• Shape of molecules

• Bond angles

• Bond formation

 Types of Hybridisation

1. sp Hybridisation

• Mixing: 1 s + 1 p

• Number of hybrid orbitals: 2

• Geometry: Linear

• Bond angle: 180°

 Example:

• BeCl₂

• CO₂

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2. sp² Hybridisation

• Mixing: 1 s + 2 p

• Number of hybrid orbitals: 3

• Geometry: Trigonal planar

• Bond angle: 120°

Example:

• BF₃

• Ethene (C₂H₄)

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3. sp³ Hybridisation

• Mixing: 1 s + 3 p

• Number of hybrid orbitals: 4

• Geometry: Tetrahedral

• Bond angle: 109.5°

Example:

• CH₄ (methane)

• NH₃

• H₂O

Note:

• NH₃ → Trigonal pyramidal (1 lone pair)

• H₂O → Bent shape (2 lone pairs)

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4. sp³d Hybridisation

• Mixing: 1 s + 3 p + 1 d

• Number of hybrid orbitals: 5

• Geometry: Trigonal bipyramidal

Example:

• PCl₅

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5. sp³d² Hybridisation

• Mixing: 1 s + 3 p + 2 d

• Number of hybrid orbitals: 6

• Geometry: Octahedral

Example:

• SF₆

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  Key Concept: Steric Number

 Steric Number =
Number of sigma (σ) bonds + lone pairs on central atom

Steric Number	Hybridisation	Geometry
2	sp	Linear
3	sp²	Trigonal planar
4	sp³	Tetrahedral
5	sp³d	Trigonal bipyramidal
6	sp³d²	Octahedral

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 Steps to Determine Hybridisation

1. Draw Lewis structure

2. Count σ bonds

3. Count lone pairs

4. Calculate steric number

5. Assign hybridisation

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 Important Notes

✔ Only sigma bonds are counted
✔ Pi (π) bonds do NOT affect hybridisation
✔ Lone pairs change shape, not hybridisation
✔ Hybrid orbitals are equivalent in energy

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 Shape vs Hybridisation

Molecule	Hybridisation	Shape
CH₄	sp³	Tetrahedral
NH₃	sp³	Trigonal pyramidal
H₂O	sp³	Bent
CO₂	sp	Linear
BF₃	sp²	Trigonal planar

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 Visual Summary

• sp → straight line

• sp² → flat triangle

• sp³ → 3D tetrahedron

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 Common Mistakes to Avoid

❌ Counting π bonds
❌ Ignoring lone pairs
❌ Mixing shape and hybridisation
❌ Forgetting steric number

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 Quick Trick

Hybridisation = Number of regions of electron density

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 Extra: Hybridisation of Carbon

Compound	Hybridisation
Alkane (single bond)	sp³
Alkene (double bond)	sp²
Alkyne (triple bond)	sp