JEE Main Chemistry Chemical Bonding & Molecular Structure 2027: VSEPR, Hybridisation & Molecular Orbital Theory
VSEPR shapes, hybridisation, molecular orbital theory, bond order and hydrogen bonding, taught with worked examples for one of JEE Chemistry's biggest chapters.
Edurack
September 28, 2026
Predicting the shape of XeF₄ in ten seconds, or telling whether O₂⁻ is paramagnetic, is not magic. It is a repeatable method. Chemical Bonding is one of the highest-yield chapters in JEE Main Chemistry, and it rewards students who practise the method until it is automatic.
Count electron pairs, then place them as far apart as possible. That is VSEPR in one sentence.
Chapter at a Glance
| Snapshot | Detail |
|---|---|
| NTA unit | Unit 3 of 20: Chemical Bonding & Molecular Structure |
| Priority (trend-based) | High |
| Typical question style | Shape and hybridisation MCQs, bond order and magnetic behaviour from MOT |
| Best first step | Master VSEPR shapes first, then bond order from MOT |
Priority reflects past-paper trends, not an official NTA weightage.
What the NTA Syllabus Covers
- Kossel-Lewis approach, ionic and covalent bonds, lattice enthalpy
- Electronegativity, Fajan's rule, dipole moment, VSEPR theory and shapes of simple molecules
- Valence bond theory, hybridisation involving s, p and d orbitals, resonance
- Molecular orbital theory, LCAO, bonding and antibonding orbitals, molecular orbital configurations of homonuclear diatomics, bond order, bond length and bond energy
- Metallic bonding, hydrogen bonding and its applications
Master These Topics
1. VSEPR: Shape from Electron Pairs
Count bond pairs plus lone pairs on the central atom (the steric number). That number fixes the hybridisation, and lone pairs then modify the shape.
| Steric number | Hybridisation | Examples and shapes |
|---|---|---|
| 2 | sp | BeCl₂ linear |
| 3 | sp² | BF₃ trigonal planar, SO₂ bent |
| 4 | sp³ | CH₄ tetrahedral, NH₃ pyramidal, H₂O bent |
| 5 | sp³d | PCl₅ trigonal bipyramidal, SF₄ see-saw, ClF₃ T-shaped, XeF₂ linear |
| 6 | sp³d² | SF₆ octahedral, BrF₅ square pyramidal, XeF₄ square planar |
Worked example: XeF₄ has 4 bond pairs and 2 lone pairs on xenon, steric number 6, so sp³d². The two lone pairs sit opposite each other, leaving a square planar molecule.
Trap: Lone pairs occupy more space than bond pairs, so bond angles shrink as lone pairs increase: CH₄ (109.5°) > NH₃ (107°) > H₂O (104.5°).
2. Molecular Orbital Theory: Bond Order and Magnetism
Bond order = (N_b − N_a) / 2, where N_b and N_a are electrons in bonding and antibonding orbitals. Higher bond order means shorter and stronger bonds. Unpaired electrons mean paramagnetic; all paired means diamagnetic.
Orbital energy order differs: for O₂ and F₂ the σ(2p) lies below π(2p), while for Li₂ to N₂ the π(2p) lies below σ(2p).
Worked examples:
- N₂ (10 valence electrons): N_b = 8, N_a = 2, bond order 3, diamagnetic.
- O₂ (12 valence electrons): N_b = 8, N_a = 4, bond order 2, paramagnetic with two unpaired electrons in π∗ orbitals.
- O₂⁻ has bond order 1.5, O₂²⁻ has bond order 1, and O₂⁺ has bond order 2.5.
So the bond length order is O₂⁺ < O₂ < O₂⁻ < O₂²⁻.
3. Fajan's Rule and Ionic Character
An ionic bond gains covalent character when the cation is small and highly charged and the anion is large and highly polarisable. So AlCl₃ is more covalent than NaCl, and AgI more covalent than AgCl.
4. Hydrogen Bonding
Hydrogen bonding occurs when H is bonded to F, O or N. Intermolecular H-bonding raises boiling point (H₂O, HF), while intramolecular H-bonding, as in o-nitrophenol, lowers it and reduces solubility in water compared with p-nitrophenol.
Common Traps to Avoid
- Ignoring lone pairs when deciding molecular shape.
- Using the wrong MO energy order for O₂ versus N₂.
- Confusing shape (positions of atoms) with electron geometry (positions of all pairs).
- Assuming a molecule with polar bonds is always polar. Symmetry can cancel the dipoles, as in CO₂ and BF₃.
60-Second Revision Sheet
- Steric number: 2 sp, 3 sp², 4 sp³, 5 sp³d, 6 sp³d²
- Bond order
(N_b − N_a)/2; bond length falls as bond order rises - N₂ bond order 3; O₂ bond order 2 and paramagnetic
- Fajan's rule: small, highly charged cation and large anion favour covalency
Your Study Plan
- Day 1: Lewis structures, formal charge and resonance.
- Day 2: VSEPR and hybridisation for 30 species.
- Day 3: MOT configurations, bond order and magnetism for diatomics and their ions.
- Day 4: dipole moment, hydrogen bonding, Fajan's rule and a timed set.
Practice Chemical Bonding & Molecular Structure Questions Free → (opens in a new tab)
Continue Your Chemistry Journey
- Previous chapter: Atomic Structure
- Next chapter: Chemical Thermodynamics
- All JEE Main Chemistry chapters
- Complete JEE Main Syllabus 2027 guide
Frequently Asked Questions
Is O₂ paramagnetic or diamagnetic?
Paramagnetic. Molecular orbital theory places two unpaired electrons in the degenerate π∗ orbitals.
How do I find the hybridisation quickly?
Add the number of sigma bonds and lone pairs on the central atom. Two gives sp, three gives sp², four gives sp³, five gives sp³d and six gives sp³d².