Short Q&A for Chemical Bonding and Molecular Structure (Class 11 NCERT)

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Chemical Bonding and Molecular Structure

111 Short Q&A • NCERT Class 11 Chemistry

Class 11 JEE / NEET

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111 Short Q&A for Chemical Bonding

Part 1: Basic Concepts and Valence Bond Theory (VBT)
1. Q1: What is a Chemical Bond?
   A: The attractive force that holds various constituents (atoms, ions) together in different chemical species.
2. Q2: Why do atoms combine to form molecules?
   A: To acquire a stable configuration (usually octet or duplet).
3. Q3: State the Octet Rule.
   A: Atoms tend to achieve eight electrons in their valence shell.
4. Q4: Give one example of a molecule that violates the Octet Rule (incomplete octet).
   A: BCl₃ or LiCl.
5. Q5: Give one example of a molecule that violates the Octet Rule (expanded octet).
   A: SF₆ or PCl₅.
6. Q6: Who proposed the concept of electrovalent (ionic) and covalent bonds?
   A: Kossel and Lewis.
7. Q7: What is an Ionic Bond?
   A: The electrostatic force of attraction between two oppositely charged ions formed by complete transfer of electrons.
8. Q8: What is a Covalent Bond?
   A: A bond formed by the mutual sharing of electrons between two atoms.
9. Q9: What are Lewis Dots Structures?
   A: Diagrams showing valence electrons as dots around the atomic symbol.
10. Q10: Define Bond Enthalpy.
    A: The energy required to break one mole of a particular type of bond in the gaseous state.
11. Q11: Define Bond Length.
    A: The equilibrium distance between the nuclei of two bonded atoms in a molecule.
12. Q12: What is the relationship between bond order and bond length?
    A: Higher the bond order, shorter the bond length.
13. Q13: What is a Coordinate Bond (or Dative Bond)?
    A: A bond where both shared electrons are contributed by one atom only.
14. Q14: What is Lattice Enthalpy?
    A: The energy required to completely separate one mole of a solid ionic compound into gaseous constituent ions.
15. Q15: What is the driving force for the formation of an ionic bond?
    A: High Lattice Enthalpy and low Ionization Enthalpy/high Electron Gain Enthalpy.
16. Q16: Which type of bond is directional?
    A: Covalent bond.
17. Q17: Which type of bond is non-directional?
    A: Ionic bond.
18. Q18: What is the principle of Valence Bond Theory (VBT)?
    A: Covalent bond formation occurs via the overlapping of atomic orbitals.
19. Q19: What is a σ (sigma) bond?
    A: A bond formed by head-on (axial) overlap of orbitals.
20. Q20: What is a π (pi) bond?
    A: A bond formed by sideways (lateral) overlap of orbitals.
21. Q21: Which is stronger, a σ bond or a π bond?
    A: σ bond (due to greater extent of overlap).
22. Q22: What kind of bond is the first bond formed between two atoms?
    A: Always a σ bond.
23. Q23: How many σ and π bonds are in N₂ molecule?
    A: One σ and two π bonds (a triple bond).
Part 2: VSEPR Theory and Molecular Geometry
24. Q24: What does VSEPR stand for?
    A: Valence Shell Electron Pair Repulsion Theory.
25. Q25: What is the main postulate of VSEPR theory?
    A: Electron pairs (both lone and bond pairs) repel each other and arrange themselves to minimize repulsion.
26. Q26: Rank the repulsion order: lp-lp, lp-bp, bp-bp.
    A: lp-lp > lp-bp > bp-bp (Lone pair-Lone pair is highest).
27. Q27: What is the geometry of a molecule with two bond pairs and zero lone pairs (AB₂)?
    A: Linear (180°).
28. Q28: What is the geometry of BF₃?
    A: Trigonal Planar (120°).
29. Q29: What is the geometry of CH₄?
    A: Tetrahedral (109.5°).
30. Q30: What is the geometry of PCl₅?
    A: Trigonal Bipyramidal.
31. Q31: What is the geometry of SF₆?
    A: Octahedral.
32. Q32: What is the shape of NH₃?
    A: Trigonal Pyramidal (due to one lone pair).
33. Q33: What is the bond angle in NH₃?
    A: 107° (less than 109.5° due to lp-bp repulsion).
34. Q34: What is the shape of H₂O?
    A: Bent or V-shape (due to two lone pairs).
35. Q35: What is the bond angle in H₂O?
    A: 104.5° (less than 109.5° due to two lp-bp repulsions).
36. Q36: What is the geometry of XeF₄?
    A: Square Planar (six pairs, two lone pairs on axial positions).
37. Q37: What is the hybridization and shape of IF₅?
    A: sp³d², Square Pyramidal.
38. Q38: What is the hybridization and shape of I₃⁻ ion?
    A: sp³d, Linear (three lone pairs on equatorial positions).
39. Q39: What is the shape of SF₄?
    A: See-saw or Distorted Tetrahedral.
Part 3: Hybridization and Polarity
40. Q40: Define Hybridization.
    A: The process of intermixing of atomic orbitals of slightly different energies to form a new set of equivalent orbitals.
41. Q41: How many sp hybrid orbitals are formed from one s and one p orbital?
    A: Two sp hybrid orbitals.
42. Q42: What is the geometry and bond angle of sp² hybridization?
    A: Trigonal Planar, 120°.
43. Q43: What is the geometry and bond angle of sp³ hybridization?
    A: Tetrahedral, 109.5°.
44. Q44: What is the percentage of s-character in an sp hybrid orbital?
    A: 50%.
45. Q45: What is the hybridization of the central atom in BeCl₂?
    A: sp (Linear, 180°).
46. Q46: What is the hybridization of the C atom in C₂H₄ (Ethene)?
    A: sp² (Trigonal Planar).
47. Q47: What is the hybridization of the central N atom in NH₃?
    A: sp³.
48. Q48: What is the hybridization of C in CO₂?
    A: sp (Linear).
49. Q49: What is a Polar Covalent Bond?
    A: A covalent bond where the shared electron pair is unequally attracted by the two atoms (due to EN difference).
50. Q50: Define Dipole Moment (μ).
    A: The product of the magnitude of the charge (q) and the distance (d) between the centres of positive and negative charges (μ=q×d).
51. Q51: What is the SI unit of Dipole Moment?
    A: Coulomb meter (C m), usually expressed in Debye (D).
52. Q52: Is CO₂ a polar or non-polar molecule?
    A: Non-polar (due to linear shape, dipoles cancel out).
53. Q53: Is H₂O a polar or non-polar molecule?
    A: Polar (due to bent shape, net dipole moment).
54. Q54: Arrange HCl, HF, HBr, HI in increasing order of bond polarity.
    A: HI < HBr < HCl < HF (based on EN difference).
55. Q55: Which molecule among NH₃ and NF₃ has a higher dipole moment?
    A: NH₃ (Lone pair and N-H bond dipoles are in the same direction, adding up).
56. Q56: If a molecule has a net dipole moment of zero, what does it usually imply about its structure?
    A: It has a symmetrical structure.
Part 4: Molecular Orbital Theory (MOT) and Resonance
57. Q57: What is the fundamental concept of Molecular Orbital Theory (MOT)?
    A: Atomic orbitals combine to form an equal number of Molecular Orbitals (MOs).
58. Q58: What is an LCAO?
    A: Linear Combination of Atomic Orbitals.
59. Q59: What are the two types of molecular orbitals formed by LCAO?
    A: Bonding Molecular Orbitals (BMO) and Anti-Bonding Molecular Orbitals (ABMO).
60. Q60: Which MO is lower in energy, BMO or ABMO?
    A: BMO (stabilizing, increases electron density between nuclei).
61. Q61: Write the formula for Bond Order according to MOT.
    A: Bond Order = 1/2(N_b − N_a) (N_b = e⁻ in BMO, N_a = e⁻ in ABMO).
62. Q62: What does a zero or negative bond order indicate?
    A: The molecule is unstable and does not exist.
63. Q63: Is He₂ stable? Justify using bond order.
    A: No, Bond Order = 0 (σ1s²σ^*1s²).
64. Q64: What is the bond order of O₂?
    A: 2 (Double bond).
65. Q65: What is the bond order of O₂⁺?
    A: 2.5.
66. Q66: What is the bond order of O₂⁻ (Superoxide ion)?
    A: 1.5.
67. Q67: What magnetic property does a molecule with unpaired electrons exhibit?
    A: Paramagnetism.
68. Q68: What magnetic property does a molecule with all paired electrons exhibit?
    A: Diamagnetism.
69. Q69: Is O₂ (Oxygen) paramagnetic or diamagnetic?
    A: Paramagnetic (two unpaired e⁻ in π^*2p orbitals).
70. Q70: Is N₂ (Nitrogen) paramagnetic or diamagnetic?
    A: Diamagnetic (all electrons are paired).
71. Q71: What are Resonance Structures (or Canonical Forms)?
    A: Two or more Lewis structures that collectively describe the electronic structure of a single molecule.
72. Q72: What is the Resonance Hybrid?
    A: The actual structure of the molecule which is the intermediate of all resonance structures.
73. Q73: Give one example of a molecule that exhibits resonance.
    A: O₃ (Ozone), CO₃²⁻ (Carbonate ion), or Benzene (C₆H₆).
74. Q74: How does resonance affect the stability of a molecule?
    A: Resonance increases the stability of the molecule.
75. Q75: What is the bond order of CO₃²⁻?
    A: 4/3 or 1.33 (four bonds shared among three sites).
Part 5: Fajan's Rules and Intermolecular Forces
76. Q76: What do Fajan's Rules predict?
    A: The degree of covalent character in an ionic bond.
77. Q77: According to Fajan's Rules, which ion favors maximum covalent character?
    A: Small Cation and Large Anion.
78. Q78: Why does a small cation favor covalent character?
    A: Its high polarizing power (high charge density).
79. Q79: Define Polarizability of an ion.
    A: The ability of an anion's electron cloud to be distorted by the cation.
80. Q80: Rank the following in increasing covalent character: LiCl, NaCl, KCl.
    A: KCl < NaCl < LiCl (Cation size K⁺ > Na⁺ > Li⁺).
81. Q81: What type of attraction exists in a purely ionic solid?
    A: Electrostatic (Coulombic) attraction.
82. Q82: What are Intermolecular Forces (IMFs)?
    A: Attractive forces between molecules.
83. Q83: What are the five major types of Intermolecular Forces?
    A: Dispersion (London) forces, Dipole-Dipole, Dipole-Induced Dipole, Ion-Dipole, Hydrogen Bonding.
84. Q84: Which type of IMF is present in all molecules?
    A: London Dispersion Forces (or Van der Waals forces).
85. Q85: What is the strongest type of IMF?
    A: Hydrogen Bonding.
86. Q86: What is Hydrogen Bonding?
    A: A special case of dipole-dipole interaction between an H atom bonded to a highly electronegative atom (F,O,N) and another electronegative atom.
87. Q87: Why does water have an unusually high boiling point?
    A: Extensive Hydrogen Bonding.
88. Q88: What is the difference between Intramolecular and Intermolecular H-bonding?
    A: Intra is within the same molecule; Inter is between two different molecules.
89. Q89: Which type of H-bonding is responsible for the associated nature of alcohols?
    A: Intermolecular H-bonding.
Part 6: Miscellaneous Concepts and Hybridization Details
90. Q90: What are the main limitations of the Octet Rule?
    A: Incomplete/Expanded octets, and it fails for odd-electron molecules.
91. Q91: What is the maximum number of lone pairs on the central atom in XeF₂?
    A: Three (linear shape, sp³d hybridization).
92. Q92: What is the hybridization of the central atom in H₂O?
    A: sp³ (two bond pairs, two lone pairs).
93. Q93: What is the hybridization of the central atom in ICl₄⁻?
    A: sp³d².
94. Q94: What is the type of overlap in a C-C single bond in C₂H₆?
    A: sp³-sp³ σ overlap.
95. Q95: What is the type of overlap in a C-H bond in CH₄?
    A: sp³-s σ overlap.
96. Q96: Define Bond Order (classical definition).
    A: The number of bonds between two atoms in a molecule.
97. Q97: What is the general electronic configuration of the ABMO for a p orbital combination?
    A: π^*2p and σ^*2p.
98. Q98: What is the covalent character of a compound where the electronegativity difference is >1.7?
    A: Predominantly Ionic.
99. Q99: What is the covalent character of a compound where the electronegativity difference is ≈0?
    A: Predominantly Covalent (pure covalent).
100. Q100: Why is the s-character of a hybrid orbital important?
     A: Higher s-character leads to shorter bond length and greater bond strength.
101. Q101: What is the shape of a molecule with sp³d hybridization and one lone pair?
     A: See-saw.
102. Q102: What is the shape of a molecule with sp³d hybridization and three lone pairs?
     A: Linear.
103. Q103: What is the maximum possible bond order for a diatomic molecule?
     A: 3 (as in N₂ and CO).
104. Q104: What is the common oxidation state of a Group 1 element in an ionic compound?
     A: +1.
105. Q105: Which carbon atom is sp² hybridized in CH₃CHO (Acetaldehyde)?
     A: The Carbonyl Carbon (>C=O).
106. Q106: Why are ionic compounds hard and brittle?
     A: Strong electrostatic forces lead to a rigid structure, and displacement causes repulsion between same-charged ions.
107. Q107: Why are LiCl and MgCl₂ more covalent than KCl and CaCl₂?
     A: Smaller Li⁺ and Mg²⁺ cations have higher polarizing power (Fajan's Rule).
108. Q108: Is ice denser than liquid water? Why?
     A: No, due to the open cage-like structure formed by H-bonding in the solid state.
109. Q109: What is the geometry of the CO₃²⁻ ion?
     A: Trigonal Planar.
110. Q110: Name the only non-metal that typically forms an ionic bond with metals.
     A: Fluorine (F) (due to its highest electronegativity).
111. Q111: Name the type of hybrid orbitals involved in sp³d² hybridization.
     A: one s, three p, and two d orbitals.

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