Chemical Bonding and Molecular Structure — Previous Year Questions (Class 11 Chemistry)
Understand how atoms bond to form molecules through ionic, covalent, and coordinate covalent bonds. Explore molecular geometry, hybridization, and intermol
TL;DR: Understand how atoms bond to form molecules through ionic, covalent, and coordinate covalent bonds. Explore molecular geometry, hybridization, and int…
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Understand how atoms bond to form molecules through ionic, covalent, and coordinate covalent bonds. Explore molecular geometry, hybridization, and intermol
Chemical Bonding and Molecular Structure — Previous Year Questions with Solutions
Q (2023, 3 marks): Explain the formation of sodium chloride (NaCl) using the concept of ionic bonding.
Answer: Sodium Chloride Formation:
Sodium (Na):
Electron configuration: 1s^2 2s^2 2p^6 3s^1
Loses 1 electron from 3s orbital
Formed Na+ ion with configuration [Ne]
Chlorine (Cl):
Electron configuration: 1s^2 2s^2 2p^6 3s^2 3p^5
Gains 1 electron in 3p orbital
Formed Cl- ion with configuration [Ar]
Ionic Bonding:
Na transfers its valence electron to Cl
Electrostatic attraction between Na+ and Cl- ions
Na+ and Cl- combine in 1:1 ratio to form NaCl
Both ions achieve noble gas configuration (stable octet)
Q (2022, 3 marks): Determine the hybridization and shape of ammonia (NH3) molecule.
Answer: Ammonia (NH3):
Nitrogen electron configuration: 1s^2 2s^2 2p^3
Valence electrons = 5
Number of bonds with H = 3
Number of lone pairs = 1
Total electron pairs around N = 4
Hybridization:
With 4 electron pairs, hybridization = sp^3
Molecular geometry:
Electron geometry: Tetrahedral
Molecular geometry: Trigonal pyramidal
The lone pair repels bonding pairs more strongly, resulting in a pyramidal shape
Bond angle: approximately 107° (less than 109.5° due to lone pair repulsion)
Q (2024, 2 marks): Explain the difference between a sigma (σ) bond and a pi (π) bond.
Answer: Sigma (σ) Bond:
- Direct overlap of atomic orbitals along the internuclear axis
- Can be formed by s-s, s-p, p-p overlap
- Electron density is symmetrical around the bond axis
- Allows free rotation around the bond
- Stronger bond (higher bond strength)
Pi (π) Bond:
- Lateral overlap of p orbitals parallel to the internuclear axis
- Electron density is concentrated above and below the bond axis
- Does not allow free rotation
- Weaker bond than sigma bond
- Always occurs in addition to a sigma bond
Example: C=C has 1 σ bond and 1 π bond
Q (2023, 3 marks): Draw the Lewis structure of carbon dioxide (CO2) and explain the bonding.
Answer: Carbon Dioxide (CO2):
Lewis Structure:
O=C=O
Bonding explanation:
Carbon: 4 valence electrons
Oxygen: 6 valence electrons each
Total = 4 + 6 + 6 = 16 electrons
Carbon forms:
- Double bond with first O (1 σ + 1 π bond)
- Double bond with second O (1 σ + 1 π bond)
Total bonds: 2 σ bonds and 2 π bonds
Molecular shape:
Linear geometry
Bond angle = 180°
Carbon hybridization = sp
Q (2022, 2 marks): Predict the molecular geometry of methane (CH4) using VSEPR theory.
Answer: Methane (CH4):
Carbon valence electrons = 4
Number of C-H bonds = 4
Number of lone pairs on C = 0
Total electron pairs = 4
VSEPR Prediction:
With 4 bonding pairs and 0 lone pairs
Electron geometry = Tetrahedral
Molecular geometry = Tetrahedral
Hybridization = sp^3
Bond angle = 109.5°
All four C-H bonds are equivalent
The molecule has maximum symmetry
Q (2024, 3 marks): Explain the concept of electronegativity and how it affects chemical bonding.
Answer: Electronegativity:
Definition: The ability of an atom to attract electrons towards itself in a covalent bond
Characteristics:
- Increases from left to right across a period
- Decreases down a group
- Fluorine is most electronegative (3.98 on Pauling scale)
Effect on Bonding:
Polar Covalent Bond:
- When electronegativity difference is 0.5-1.9
- Electron pair is not equally shared
- Creates partial charges (δ+ and δ-)
Example: H-Cl
Ionic Bond:
- When electronegativity difference > 1.9
- Complete transfer of electrons
- Formation of cations and anions
Example: Na-Cl
Non-polar Covalent Bond:
- When electronegativity difference < 0.5
- Electrons equally shared
- No partial charges
Example: C-C
Frequently Asked Questions
What is the difference between bond order and bond length?
Bond order refers to the number of electron pairs shared between two atoms (single, double, triple bonds), while bond length is the distance between the nuclei of bonded atoms. As bond order increases, bond length decreases and bond strength increases.
Why does BF3 not follow the octet rule?
Boron in BF3 forms only three bonds with fluorine atoms, resulting in only 6 electrons around boron. Boron is electron-deficient and cannot achieve an octet. However, it is still stable because it has a complete valence shell (all s and p orbitals of the second shell are involved).
More Class 11 Chemistry PYQs
- Electrochemistry
- Solutions
- Chemical Kinetics
- Coordination Compounds
- Haloalkanes and Haloarenes
- Aldehydes Ketones and Carboxylic Acids
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