Chemical Bonding
Key Concepts
| # | Concept | Explanation |
|---|---|---|
| 1 | Ionic Bond | Transfer of electrons from metal to non-metal; forms ions that attract (NaCl). |
| 2 | Covalent Bond | Sharing of electrons between non-metals; can be single, double or triple (H₂O, CO₂). |
| 3 | Metallic Bond | “Sea” of delocalised electrons surrounding metal cations; explains conductivity & malleability. |
| 4 | Octet Rule | Atoms tend to gain/lose/share electrons until 8 electrons in outermost shell (stable like noble gases). |
| 5 | Electronegativity | Tendency of an atom to pull shared electrons; difference >1.7 → ionic, <1.7 → covalent. |
| 6 | Fajan’s Rule | Covalent character ↑ with small cation, large anion & high charge (AlI₃ > AlF₃). |
| 7 | VSEPR Theory | Shape of molecule decided by repulsion between electron pairs around central atom (NH₃ → pyramidal). |
| 8 | Hybridisation | Mixing of atomic orbitals to form new orbitals (sp³ in CH₄, sp² in C₂H₄, sp in C₂H₂). |
15 Practice MCQs
1. Which compound contains both ionic & covalent bonds?
A. MgCl₂ B. NH₄Cl C. CH₄ D. H₂O **Answer:** B. NH₄Cl **Solution:** NH₄⁺ & Cl⁻ are ionic; inside NH₄⁺, N–H bonds are covalent. **Shortcut:** “Ammonium salts always dual.” **Tag:** Mixed bonding2. The bond in sodium chloride is formed by:
A. Sharing B. Transfer C. Both D. None **Answer:** B. Transfer **Shortcut:** Metal + non-metal → electron transfer. **Tag:** Ionic bond3. Maximum covalency of carbon is:
A. 2 B. 3 C. 4 D. 6 **Answer:** C. 4 **Shortcut:** Carbon has 4 valence electrons → can form 4 bonds. **Tag:** Covalency4. Electronegativity order correct is:
A. F>O>N B. F>N>O C. O>F>N D. N>O>F **Answer:** A. F>O>N **Shortcut:** “FON” descending series. **Tag:** Electronegativity trend5. Which molecule has linear shape?
A. H₂O B. CO₂ C. NH₃ D. CH₄ **Answer:** B. CO₂ **Shortcut:** No lone pair on central C → 2 double bonds → linear. **Tag:** VSEPR6. sp³ hybridisation is present in:
A. BeCl₂ B. BF₃ C. CH₄ D. C₂H₂ **Answer:** C. CH₄ **Shortcut:** 4 single bonds → sp³. **Tag:** Hybridisation7. Which has highest covalent character?
A. NaCl B. MgCl₂ C. AlCl₃ D. KCl **Answer:** C. AlCl₃ **Shortcut:** Higher charge & smaller cation → more covalent (Fajan). **Tag:** Fajan’s rule8. Octet is not obeyed in:
A. CO₂ B. BF₃ C. CH₄ D. NH₃ **Answer:** B. BF₃ **Shortcut:** B has only 6e⁻ in outer shell. **Tag:** Octet exception9. Conduct electricity in molten state but not solid:
A. Diamond B. NaCl C. Graphite D. SiO₂ **Answer:** B. NaCl **Shortcut:** Ionic solids conduct only when ions free (molten/aq). **Tag:** Electrical conductivity10. Coordinate bond is present in:
A. HCl B. NH₄⁺ C. NaCl D. O₂ **Answer:** B. NH₄⁺ **Shortcut:** One atom donates both e⁻ (N→H⁺). **Tag:** Coordinate bond11. Bond formed between two chlorine atoms is:
A. Ionic B. Metallic C. Non-polar covalent D. Polar covalent **Answer:** C. Non-polar covalent **Shortcut:** Same atoms → equal sharing → non-polar. **Tag:** Bond polarity12. Which set has only covalent compounds?
A. NaCl, KBr B. H₂O, CO₂ C. MgO, CaF₂ D. NH₃, Na₂O **Answer:** B. H₂O, CO₂ **Shortcut:** Non-metal + non-metal → covalent. **Tag:** Compound type13. Number of single covalent bonds in C₂H₆:
A. 5 B. 6 C. 7 D. 8 **Answer:** C. 7 (1 C–C + 6 C–H) **Shortcut:** Draw skeleton & count. **Tag:** Bond counting14. The “electron sea” model explains:
A. NaCl B. Graphite C. Copper D. Ice **Answer:** C. Copper **Shortcut:** Metals → sea of e⁻ → conductivity. **Tag:** Metallic bonding15. Correct statement:
A. Ionic compounds have low melting point B. Covalent solids conduct electricity C. Metallic bonds are directional D. Covalent bonds are directional **Answer:** D. Covalent bonds are directional **Shortcut:** Only covalent bonds have fixed angles. **Tag:** Bond propertiesSpeed Tricks
| Situation | Shortcut | Example |
|---|---|---|
| Metal + Non-metal | Ionic bond, electron transfer | NaCl |
| ΔEN >1.7 | Ionic; ΔEN <1.7 | HCl |
| Count σ bonds | Single=1, double=1σ+1π, triple=1σ+2π | C₂H₄ → 5σ |
| Hybridisation | Bond pairs + lone pairs = 2(sp), 3(sp²), 4(sp³) | NH₃: 3+1=4 → sp³ |
| Octet exception | Molecules with B, Be, Al or odd e⁻ species | NO, BF₃ |
Quick Revision
| Point | Detail |
|---|---|
| 1 | Ionic compounds conduct only when molten or aqueous. |
| 2 | Covalent compounds have low mp/bp & poor conductivity. |
| 3 | Higher lattice energy → higher melting point of ionic solid. |
| 4 | Electronegativity: F(4.0) > O(3.5) > N(3.0) > Cl(3.0). |
| 5 | sp hybridisation → linear (180°), sp² → trigonal planar (120°), sp³ → tetrahedral (109.5°). |
| 6 | Bond angle order: sp (180°) > sp² (120°) > sp³ (109.5°). |
| 7 | Coordinate bond = dative bond; arrow (→) from donor to acceptor. |
| 8 | Resonance stabilises molecules; e.g., O₃, CO₃²⁻. |
| 9 | Fajan’s rule: covalent character ∝ charge²/(cation size). |
| 10 | Graphite conducts due to delocalised π-electrons within layers. |
BETA
