Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Quick Summary
Chemical bonding explains why atoms combine and predicts molecular shapes and properties. This chapter is NEET-critical (3–5 questions per year) — VSEPR, hybridisation, and MO theory shapes are frequently tested. Board exams test Lewis structures, VSEPR geometry, and MO energy diagrams.
Key Concepts and Definitions
- Ionic bond: Transfer of electrons; formed between metals and non-metals (high electronegativity difference > 1.7)
- Covalent bond: Sharing of electrons; formed between non-metals
- Coordinate (dative) bond: Both electrons donated by one atom (e.g., BF₃ + NH₃, H₃O⁺)
- Bond length: Distance between nuclei of bonded atoms; decreases as bond order increases
- Bond energy: Energy to break 1 mol of bond; increases as bond order increases
- σ bond: End-to-end overlap; free rotation possible
- π bond: Side-to-side overlap; no free rotation
- Dipole moment: μ = q × d; measure of polarity; zero for symmetric molecules
Hybridisation Summary
| Hybridisation | Geometry | Bond angle | Example |
|---|---|---|---|
| sp | Linear | 180° | BeCl₂, CO₂, C₂H₂ |
| sp² | Trigonal planar | 120° | BF₃, C₂H₄, SO₃ |
| sp³ | Tetrahedral | 109.5° | CH₄, CCl₄ |
| sp³ (2 lone pairs) | Bent/V-shape | 104.5° | H₂O |
| sp³ (1 lone pair) | Pyramidal | 107° | NH₃ |
| sp³d | Trigonal bipyramidal | 90°, 120° | PCl₅ |
| sp³d² | Octahedral | 90° | SF₆ |
VSEPR Shapes — Key Molecules
| Molecule | Electron Pairs (total) | Shape |
|---|---|---|
| BeCl₂ | 2 BP, 0 LP | Linear |
| BF₃ | 3 BP, 0 LP | Trigonal planar |
| CH₄ | 4 BP, 0 LP | Tetrahedral |
| NH₃ | 3 BP, 1 LP | Trigonal pyramidal |
| H₂O | 2 BP, 2 LP | Bent |
| PCl₅ | 5 BP, 0 LP | Trigonal bipyramidal |
| SF₆ | 6 BP, 0 LP | Octahedral |
MO Theory — Bond Orders
| Molecule | Bond Order | Magnetic Property |
|---|---|---|
| H₂ | 1 | Diamagnetic |
| He₂ | 0 | Does not exist |
| Li₂ | 1 | Diamagnetic |
| O₂ | 2 | Paramagnetic |
| N₂ | 3 | Diamagnetic |
| F₂ | 1 | Diamagnetic |
MO Energy order (up to N₂): σ1s < σ1s < σ2s < σ2s < π2p = π2p < σ2p < π2p = π2p < σ*2p
Important Questions
One Mark (5)
- Define hybridisation.
- What is the bond angle in CH₄?
- Which is stronger: single bond or double bond? Give reason.
- Define bond order.
- Why is H₂O bent but CO₂ is linear?
Short Answer 3-mark (3)
- Explain sp³ hybridisation of carbon in methane with a diagram.
- Draw the Lewis structure of NO₃⁻ and explain its resonance.
- What is the geometry of NH₃? Why is the bond angle less than tetrahedral?
Long Answer 5-mark (2)
- Explain VSEPR theory with examples of BF₃, CH₄, NH₃, and H₂O. Compare their geometries.
- Draw the MO energy diagram for O₂. Calculate bond order and state magnetic character.
Common Mistakes
- Confusing molecular geometry with electron geometry — lone pairs affect shape but are not counted in molecular name.
- Writing sp² for NH₃ — it is sp³ (with one lone pair).
- Forgetting that O₂ is paramagnetic (2 unpaired electrons in degenerate π* orbitals).
- Thinking resonance structures alternate — they are simultaneous averages.
Board Exam Tips
- VSEPR shape questions appear in both 1-mark and 3-mark formats.
- MO theory and bond order of O₂, N₂, F₂ are guaranteed NEET questions.
- Hybridisation of carbon in different compounds (CH₄, C₂H₄, C₂H₂) is a frequent topic.
- Resonance of ozone, benzene, carbonate ion is a 3-mark board question.
Revision Checklist
- [ ] Hybridisation table with geometry, angle, and example written from memory
- [ ] VSEPR geometry drawn for 7 key molecules
- [ ] MO bond orders for H₂, N₂, O₂, F₂ computed
- [ ] Resonance structures drawn for O₃ and NO₃⁻
- [ ] Ionic vs covalent vs coordinate bond distinguished
Frequently Asked Questions
Hybridisation is the mixing of atomic orbitals of similar energy to form new hybrid orbitals of equal energy and shape. Examples: sp (linear, 180°), sp² (trigonal planar, 120°), sp³ (tetrahedral, 109.5°).