Chemical Bonding and Molecular Structure – JEE Mains Chemistry

• by Zenith LMS
• Updated April 2025

1. Kossel-Lewis Approach to Bond Formation

Kossel and Lewis proposed that atoms achieve stability by attaining noble gas configuration through the transfer or sharing of electrons, forming ionic or covalent bonds respectively.

2. Ionic Bonding

• Formation: Involves transfer of electrons from a metal to a non-metal, resulting in oppositely charged ions held by electrostatic force.
• Factors Affecting Formation: Ionization energy, electron affinity, lattice energy.
• Lattice Enthalpy: Energy released when one mole of an ionic compound is formed from its gaseous ions.

3. Covalent Bonding

• Concept: Formed by mutual sharing of electrons between atoms.
• Electronegativity: Tendency of an atom to attract shared electrons. Influences bond polarity.
• Fajan’s Rule: Predicts covalent character in ionic bonds based on polarizing power and polarizability.
• Dipole Moment: Measure of bond polarity; product of charge and distance between charges.

4. VSEPR Theory and Molecular Shapes

Valence Shell Electron Pair Repulsion (VSEPR) theory predicts shapes of molecules based on repulsions between electron pairs (bonding and lone pairs).

5. Valence Bond Theory and Hybridization

• Features: Bonds are formed by overlap of atomic orbitals with paired electrons.
• Hybridization: Mixing of atomic orbitals (s, p, d) to form equivalent hybrid orbitals. Types include sp, sp2, sp3, etc.
• Resonance: Delocalization of electrons in molecules having more than one valid Lewis structure.

6. Molecular Orbital Theory (MOT)

• Features: Atomic orbitals combine to form molecular orbitals (MOs) using Linear Combination of Atomic Orbitals (LCAO).
• Types: Bonding and antibonding orbitals; sigma (σ) and pi (π) bonds.
• Electronic Configurations: Applied to diatomic molecules (e.g., O₂, N₂, B₂).
• Bond Order: (Number of bonding electrons – antibonding electrons)/2. Indicates bond strength and stability.
• Bond Length and Bond Energy: Inversely related to bond order.

7. Other Types of Bonding

• Metallic Bonding: Positive metal ions surrounded by a sea of delocalized electrons.
• Hydrogen Bonding: Attractive interaction between a hydrogen atom bonded to a highly electronegative atom (like F, O, N) and another electronegative atom. Affects boiling points, solubility, etc.