Chemical Bonding and Molecular Structure — Previous Year Questions (Class 11 Chemistry)
Chemical bonding explains how atoms combine. Study ionic, covalent, and coordinate bonds for complete understanding of molecular structure.
TL;DR: Chemical bonding explains how atoms combine. Study ionic, covalent, and coordinate bonds for complete understanding of molecular structure.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
Chemical bonding explains how atoms combine. Study ionic, covalent, and coordinate bonds for complete understanding of molecular structure.
Chemical Bonding and Molecular Structure — Previous Year Questions with Solutions
Q (2023, 3 marks): Explain ionic bonding with reference to electron transfer. Why is NaCl ionic despite containing both Na and Cl atoms?
Answer: Ionic bonding forms through electrostatic attraction between oppositely charged ions created by electron transfer.
In NaCl formation:
Na (atomic number 11): 1s² 2s² 2p⁶ 3s¹ → Na⁺: 1s² 2s² 2p⁶ (loses 1 electron, achieves Ne configuration)
Cl (atomic number 17): 1s² 2s² 2p⁶ 3s² 3p⁵ → Cl⁻: 1s² 2s² 2p⁶ 3s² 3p⁶ (gains 1 electron, achieves Ar configuration)
The Na⁺ and Cl⁻ ions are held together by strong electrostatic attraction.
NaCl is ionic because:
1. Large electronegativity difference (Na = 0.93, Cl = 3.16) causes complete electron transfer
2. Both ions achieve noble gas configuration (stability)
3. Electrostatic forces are strong in the solid state
Final Answer: NaCl is ionic due to complete electron transfer from Na to Cl, forming stable Na⁺ and Cl⁻ ions
Q (2022, 5 marks): Compare ionic and covalent bonding. Give examples of each and explain why some bonds are intermediate in character.
Answer: Ionic bonding: Complete transfer of electrons from one atom to another. Examples: NaCl, MgO, CaCl₂. Occurs between metals and nonmetals with large electronegativity difference.
Covalent bonding: Sharing of electron pairs between atoms. Examples: H₂, O₂, NH₃, CH₄. Occurs between nonmetals with small electronegativity difference.
Intermediate character (Polar covalent): Most real bonds lie between purely ionic and purely covalent.
Examples: HCl, H₂O, CO₂
Factors determining bond character:
- Electronegativity difference: ΔEN < 0.5 (covalent), 0.5-1.7 (polar covalent), > 1.7 (ionic)
- Percentage ionic character increases with electronegativity difference
Example HCl: ΔEN = 3.16 - 2.20 = 0.96 (polar covalent with ~20% ionic character)
Final Answer: Comparison given; intermediate bonds exist due to partial electron transfer and unequal sharing
Q (2023, 3 marks): Draw the Lewis structure of CO₂ and explain its linear geometry using VSEPR theory.
Answer: Lewis structure of CO₂:
Carbon (4 valence electrons) forms double bonds with two oxygen atoms.
Structure: O=C=O
Each oxygen has 2 lone pairs; carbon has 0 lone pairs.
VSEPR analysis:
- Electron pairs around C = 2 (both bonding, no lone pairs)
- Steric number = 2
- Electron geometry: Linear
- Molecular geometry: Linear
- Bond angle: 180°
The two electron domains repel maximally when positioned at 180° apart.
Final Answer: CO₂ is linear with 180° bond angle due to 2 bonding pairs and 0 lone pairs on central C atom
Q (2021, 3 marks): Explain the difference between sigma (σ) and pi (π) bonds. How many σ and π bonds are present in ethene (C₂H₄)?
Answer: Sigma bond (σ): Formed by head-on overlap of orbitals. Electron density is concentrated along the bond axis. Can freely rotate. Single bonds are always σ bonds.
Pi bond (π): Formed by lateral overlap of p orbitals. Electron density is above and below the bond axis. No rotation possible. Found in double and triple bonds.
Ethene structure: H₂C=CH₂
σ bonds: 5 (one C=C σ bond + four C-H σ bonds)
π bonds: 1 (one C=C π bond)
Total: 5σ + 1π bonds
Final Answer: Ethene has 5 sigma bonds and 1 pi bond
Q (2022, 3 marks): What is a coordinate covalent bond (dative bond)? Give two examples.
Answer: A coordinate covalent bond (or dative covalent bond) is formed when both electrons of the shared pair come from the same atom. One atom acts as electron donor (with a lone pair) and the other as electron acceptor.
Example 1: NH₃ → BF₃
Nitrogen (donor) in ammonia has a lone pair; boron (acceptor) in BF₃ has an empty orbital. Nitrogen donates the lone pair to form a coordinate bond.
Example 2: [Cu(NH₃)₄]²⁺
Four ammonia ligands coordinate to copper ion through nitrogen lone pairs. Each NH₃ is a donor; Cu²⁺ is the acceptor.
Note: Once formed, a coordinate covalent bond is identical to a regular covalent bond.
Final Answer: Two examples: NH₃-BF₃ and [Cu(NH₃)₄]²⁺
Q (2023, 5 marks): Explain hybridization in carbon atoms. What is the hybridization of carbon in ethane (C₂H₆), ethene (C₂H₄), and ethyne (C₂H₂)?
Answer: Hybridization: Mixing of atomic orbitals of similar energy to form new hybrid orbitals suitable for bonding.
In ethane (C₂H₆): C-C single bond
Carbon: sp³ hybridization (1s + 3p mix)
Each carbon forms 4σ bonds: 3 with H atoms, 1 with the other C atom
Structure is tetrahedral around each C.
In ethene (C₂H₄): C=C double bond
Carbon: sp² hybridization (1s + 2p mix, leaving 1p unhybridized)
Each carbon forms 3σ bonds (planar) + 1π bond
Geometry is trigonal planar around each C.
In ethyne (C₂H₂): C≡C triple bond
Carbon: sp hybridization (1s + 1p mix, leaving 2p unhybridized)
Each carbon forms 2σ bonds + 2π bonds
Geometry is linear around each C.
Final Answer: C₂H₆ (sp³), C₂H₄ (sp²), C₂H₂ (sp)
Frequently Asked Questions
What is electronegativity and how does it relate to bond polarity?
Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. Higher electronegativity means stronger attraction. Bond polarity increases with electronegativity difference between bonded atoms. A nonpolar covalent bond has ΔEN ≈ 0; polar covalent has ΔEN between 0.5-1.7; ionic has ΔEN > 1.7.
Why are coordinate covalent bonds important in complex ion formation?
Coordinate covalent bonds allow ligands (with lone pairs) to attach to metal ions (with empty orbitals), forming complex ions. This is the primary bonding mechanism in transition metal chemistry. Examples include [Fe(CN)₆]⁴⁻ and [Ni(en)₃]²⁺ where 'en' is ethylenediamine.
More Class 11 Chemistry PYQs
- Electrochemistry
- Solutions
- Chemical Kinetics
- Coordination Compounds
- Haloalkanes and Haloarenes
- Aldehydes Ketones and Carboxylic Acids
🤖 Stuck on any of these? Ask Syllab's free AI Tutor to explain step by step →