Class 11 Chemistry – Chemical Bonding and Molecular Structure

CBSE 2026–27 | NCERT-aligned free study resource

Why Atoms Bond

Atoms combine to attain more stable electronic arrangements. Bonding is explained using ionic, covalent and related models.

Kossel-Lewis Approach

Lewis structures represent valence electrons and help predict bonding and octet completion. Exceptions to the octet rule include incomplete octets, expanded valence shells and odd-electron species.

Ionic Bond

Ionic bonding results from electrostatic attraction between oppositely charged ions. Lattice enthalpy helps explain ionic compound stability and physical properties.

Covalent Bond and Bond Parameters

Important parameters include bond length, bond angle, bond enthalpy and bond order. Higher bond order generally corresponds to shorter and stronger bonds.

VSEPR Theory

Electron pairs around a central atom arrange themselves to minimize repulsion. Lone pairs generally repel more strongly than bonding pairs, affecting molecular geometry.

Valence Bond Theory and Hybridisation

Hybridisation describes mixing of atomic orbitals to generate equivalent hybrid orbitals. Common types include sp, sp² and sp³.

Molecular Orbital Theory

Atomic orbitals combine to form bonding and antibonding molecular orbitals. Molecular orbital theory explains bond order and magnetic behaviour of species such as O₂.

Hydrogen Bonding

Hydrogen bonding occurs when hydrogen attached to a highly electronegative atom interacts with an electronegative atom having a lone pair. It strongly influences properties such as boiling point and solubility.

MCQs

1. Shape of CH₄ is: (A) linear (B) trigonal planar (C) tetrahedral (D) bent. Answer: C.
2. Hybridisation in BF₃ is commonly described as: (A) sp (B) sp² (C) sp³ (D) dsp². Answer: B.
3. Higher bond order generally means: (A) weaker bond (B) longer bond (C) stronger, shorter bond (D) no bond. Answer: C.

Practice

1. Draw Lewis structures for selected molecules and ions.
2. Use VSEPR to predict shapes of NH₃ and H₂O.
3. Explain hydrogen bonding and its consequences.

HOTS

Why is the bond angle in NH₃ smaller than the ideal tetrahedral angle? Explain using electron-pair repulsions.

Revision

Lewis structure → electron-pair arrangement → molecular geometry → hybridisation → bond order/polarity.