Questions
5–8 MCQs per paper
Difficulty
Medium
Importance
High yield for JEE/NEET; foundation for entire inorganic chemistry.
Overview
Chemical Bonding is the foundational pillar of Inorganic Chemistry, explaining how atoms aggregate to form stable molecules. Mastering the link between electronic configuration, molecular geometry, and bond energetics is essential to predict the chemical behavior of compounds across JEE, NEET, and CUET exams.
Ionic and Covalent Bonding
Bonding arises from the tendency of atoms to achieve stable noble gas configurations via electron transfer or sharing. Focus on Fajan’s Rule, which explains the covalent character in ionic compounds based on polarizability, as this is a frequent examiner trap.
- Fajan's Rule: Covalent character increases with smaller cation size, larger anion size, and higher charge density.
- Lattice Enthalpy: Higher charge and smaller inter-ionic distance increase stability.
- Dipole Moment (µ): µ = q × d; vector sum determines molecular polarity.
- Formal Charge = (Total valence electrons) - (Total lone pair electrons) - 0.5 × (Total bonding electrons).
VSEPR Theory and Molecular Geometry
VSEPR theory predicts molecular shapes based on electron pair repulsion (lp-lp > lp-bp > bp-bp). Memorize the basic geometries associated with specific electron domains to quickly identify bond angles in polyatomic ions.
- Linear (2 domains), Trigonal Planar (3 domains), Tetrahedral (4 domains).
- Trigonal Bipyramidal (5 domains), Octahedral (6 domains).
- Lone pairs decrease bond angles from ideal values.
- Square Planar occurs in sp3d2 hybridisation with 2 lone pairs.
Hybridisation
Hybridisation explains the equivalence of bonds in molecules like CH4 by mixing atomic orbitals. Use the steric number method to calculate hybridisation quickly: Steric Number = (No. of sigma bonds + No. of lone pairs).
- sp (180°), sp2 (120°), sp3 (109.5°).
- d-orbitals involved in sp3d (axial vs equatorial bonds).
- Bent's Rule: Electronegative substituents prefer orbitals with less s-character.
- Hybridisation is not possible for isolated atoms; it is a conceptual model for molecules.
Molecular Orbital Theory (MOT)
Unlike VSEPR, MOT treats electrons as delocalized over the entire molecule, explaining magnetic properties and bond order. It is the only reliable way to predict the paramagnetic nature of species like O2 or NO.
- Bond Order = 0.5 × (Bonding electrons - Anti-bonding electrons).
- Bond Order inversely proportional to bond length; directly to bond energy.
- Paramagnetism exists if unpaired electrons are present in MO diagram.
- O2 sequence: σ1s, σ*1s, σ2s, σ*2s, σ2pz, π2px=π2py, π*2px=π*2py, σ*2pz.
Formula Sheet
Formal Charge = V - L - (B/2)
Steric Number = 0.5 * (V + M - C + A)
Bond Order = (Nb - Na) / 2
Exam Tip
Always draw the Lewis structure first; if a molecule has a central atom with lone pairs, its geometry will inevitably deviate from the ideal VSEPR bond angles.
Common Mistakes
- Ignoring the presence of lone pairs when determining the final shape of a molecule.
- Applying the O2 MO sequence to molecules like B2, C2, or N2, which ignore s-p mixing.
- Confusing formal charge with actual oxidation state.
More Revision Notes
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