A clear step-by-step approach to predicting lone pair effects, hybridisation states, and MOT magnetic properties.
Chemical Bonding explains why atoms combine to form stable molecules. It is one of the most conceptual and high-weightage chapters in Class 11 Chemistry for both boards and competitive exams.
VSEPR Theory: Molecular geometry depends on valence shell electron pairs (bonding and lone pairs). Repulsion order: Lone Pair-Lone Pair > Lone Pair-Bond Pair > Bond Pair-Bond Pair. Lone pairs distort ideal bond angles (e.g., NH3 is pyramidal with 107° angle, H2O is bent with 104.5° angle).
Hybridisation: Mixing of atomic orbitals to form equivalent hybrid orbitals. Formula for steric number: 1/2 [Valence electrons of central atom + Monovalent atoms - Cationic charge + Anionic charge]. Determines shape: sp (linear), sp2 (trigonal planar), sp3 (tetrahedral), sp3d (trigonal bipyramidal), sp3d2 (octahedral).
Molecular Orbital Theory (MOT): Linear Combination of Atomic Orbitals (LCAO) forms bonding and antibonding molecular orbitals. Bond Order = 1/2 (Nb - Na). Unpaired electrons indicate paramagnetism; paired electrons indicate diamagnetism. Dr. Aarzoo Saini provides visual MOT energy diagrams at We-Gyaan Classes.
Key Takeaways for Students
- Calculate steric number to instantly determine hybridisation state of central atom.
- Account for lone pair repulsion in VSEPR geometry distortions (NH3, H2O, SF4, XeF4).
- Calculate Molecular Orbital bond order using 1/2 (Nb - Na).
- Identify paramagnetism in molecules like O2 (2 unpaired electrons in pi* orbitals).
Authored by Dr. Aarzoo Saini
Founder & Lead Educator at We-Gyaan Classes Roorkee, with over 20 years of teaching excellence in Science and Chemistry for Board Exams, NEET, JEE, and CUET.