Valence Bond Theory and Hybridisation
sp, sp2, sp3, sp3d and sp3d2 hybrid orbitals with examples. (Chemistry › Chemical Bonding and Molecular Structure, NEET UG syllabus.)
What is Valence Bond Theory and Hybridisation?
A theory that explains the formation of covalent bonds by the overlap of half-filled atomic orbitals, each containing one electron.
Key formula / rule: Steric Number (SN) for predicting hybridisation
Key points
- Explain the fundamental principles of Valence Bond Theory.
- Define hybridisation and explain its necessity.
- Identify the types of hybridisation (sp, sp², sp³, sp³d, sp³d²) based on the central atom's environment.
- Predict the geometry and bond angles of molecules based on hybridisation.
Common exam trap
Confusing VBT with Molecular Orbital Theory (MOT).
Definitions
- Term
Valence Bond Theory (VBT)
- Meaning
A theory that explains the formation of covalent bonds by the overlap of half-filled atomic orbitals, each containing one electron.
- Term
Hybridisation
- Meaning
The process of intermixing atomic orbitals of slightly different energies belonging to the same atom to form a new set of equivalent orbitals called hybrid orbitals.
- Term
Hybrid Orbitals
- Meaning
New orbitals formed by the intermixing of atomic orbitals, which are equivalent in energy and shape and are oriented in specific directions to minimize electron repulsion.
- Term
Steric Number
- Meaning
The sum of the number of σ bonds and the number of lone pairs around a central atom, used to predict the hybridisation and geometry.
Learning objectives
Explain the fundamental principles of Valence Bond Theory.
Define hybridisation and explain its necessity.
Identify the types of hybridisation (sp, sp², sp³, sp³d, sp³d²) based on the central atom's environment.
Predict the geometry and bond angles of molecules based on hybridisation.
Provide examples of molecules exhibiting different types of hybridisation.
Differentiate between hybridised and unhybridised orbitals in a molecule.
Formulae
- Name
Steric Number (SN) for predicting hybridisation
- Note
This is a key rule/method, not a mathematical formula in the traditional sense, used to determine the type of hybridisation and subsequently the geometry.
- Expression
SN = (Number of σ bonds around central atom) + (Number of lone pairs on central atom)
- Name
Alternative method for Steric Number (SN)
- Note
Where V = number of valence electrons of the central atom, M = number of monovalent atoms (like H, F, Cl, Br, I) attached to the central atom, C = positive charge on the cation, A = negative charge on the anion. This formula is useful for quick calculation.
- Expression
SN = (1/2) * [V + M - C + A]
Prerequisites
Basic understanding of atomic structure (orbitals: s, p, d).
Lewis dot structures and octet rule.
VSEPR theory (Valence Shell Electron Pair Repulsion Theory).
Types of covalent bonds (σ and π bonds).
Common mistakes
Confusing VBT with Molecular Orbital Theory (MOT).
Incorrectly calculating the steric number, leading to wrong hybridisation and geometry.
Assuming d-orbitals always participate in hybridisation for elements in period 3 and beyond.
Not considering lone pairs when determining geometry and bond angles.
Forgetting that only σ bonds and lone pairs contribute to hybridisation, not π bonds.
Incorrectly assigning the geometry for sp³d (trigonal bipyramidal) and sp³d² (octahedral).
Keywords
Valence Bond Theory
VBT
Hybridisation
Hybrid Orbitals
sp
sp2
sp3
sp3d
sp3d2
Steric Number
Molecular Geometry
Bond Angle
Orbital Overlap
Σ Bond
Π Bond
Lone Pair
Practice preview
What is the hybridisation of the carbon atom in methane (CH4)?…
easy
The carbon atoms in ethene (C2H4) exhibit which type of hybridisation?…
easy
A molecule with sp3 hybridisation typically has which geometry and bond angle?…
medium