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
-
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 bonding -
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 bond -
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: Covalency -
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 trend -
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: VSEPR -
sp³ hybridisation is present in: A. BeCl₂ B. BF₃ C. CH₄ D. C₂H₂
Answer: C. CH₄
Shortcut: 4 single bonds → sp³.
Tag: Hybridisation -
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 rule -
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 exception -
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 conductivity -
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 bond -
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 polarity -
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 type -
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 counting -
The “electron sea” model explains: A. NaCl B. Graphite C. Copper D. Ice
Answer: C. Copper
Shortcut: Metals → sea of e⁻ → conductivity.
Tag: Metallic bonding -
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 properties
Speed 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
