Covalent Bonding & VSEPR
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- Physical Chemistry: Atomic structure, chemical bonding, thermodynamics, and equilibrium.
- Organic Chemistry: Hydrocarbons, functional groups, and reaction mechanisms.
- Inorganic Chemistry: Transition metals, coordination compounds, and the periodic table.
- Analytical Chemistry: Titrations, spectroscopy, and qualitative analysis.
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All Questions for: Covalent Bonding & VSEPR
Question 1: A covalent bond is formed by:
- A Sharing of electron pairs between atoms
- B Transfer of electrons from one atom to another
- C Electrostatic attraction between ions
- D Delocalization of electrons in a metallic lattice
Explanation: A covalent bond is the sharing of one or more electron pairs between two atoms, usually between nonmetals.
Question 2: According to VSEPR theory, the shape of a molecule is determined by:
- A Repulsion between electron pairs around the central atom
- B Nuclear charge of the central atom
- C Atomic mass of the ligands
- D Bond order of the molecule
Explanation: VSEPR (Valence Shell Electron Pair Repulsion) theory states that electron pairs around a central atom arrange themselves as far apart as possible to minimize repulsion, thereby determining molecular geometry.
Question 3: What is the molecular geometry of methane (CH₄)?
- A Tetrahedral
- B Trigonal planar
- C Square planar
- D Bent
Explanation: Carbon in CH₄ has 4 bonding pairs and 0 lone pairs (steric number 4, tetrahedral electron geometry). The molecular geometry is tetrahedral with bond angles of ~109.5°.
Question 4: What is the molecular geometry of water (H₂O)?
- A Bent
- B Linear
- C Trigonal planar
- D Tetrahedral
Explanation: Oxygen in water has 2 bonding pairs and 2 lone pairs (steric number 4). The electron geometry is tetrahedral, but the molecular geometry is bent with an angle of ~104.5°.
Question 5: What is the molecular geometry of ammonia (NH₃)?
- A Trigonal pyramidal
- B Trigonal planar
- C Tetrahedral
- D T-shaped
Explanation: N in ammonia has 3 bonding pairs and 1 lone pair (steric number 4). The molecular geometry is trigonal pyramidal with bond angles of ~107°.
Question 6: What is the molecular geometry of CO₂?
- A Linear
- B Bent
- C Trigonal planar
- D Tetrahedral
Explanation: Carbon in CO₂ has 2 double bonds and 0 lone pairs (steric number 2). The molecular geometry is linear with a 180° bond angle.
Question 7: What is the molecular geometry of BF₃?
- A Trigonal planar
- B Trigonal pyramidal
- C T-shaped
- D Tetrahedral
Explanation: Boron in BF₃ has 3 bonding pairs and 0 lone pairs (steric number 3). The molecular geometry is trigonal planar with 120° bond angles.
Question 8: What is the molecular geometry of PCl₅?
- A Trigonal bipyramidal
- B Octahedral
- C Square pyramidal
- D Tetrahedral
Explanation: Phosphorus in PCl₅ has 5 bonding pairs and 0 lone pairs (steric number 5). The molecular geometry is trigonal bipyramidal.
Question 9: What is the molecular geometry of SF₆?
- A Octahedral
- B Trigonal bipyramidal
- C Square pyramidal
- D Tetrahedral
Explanation: Sulfur in SF₆ has 6 bonding pairs and 0 lone pairs (steric number 6). The molecular geometry is octahedral with 90° bond angles.
Question 10: The bond angle in a tetrahedral molecule is approximately:
- A 109.5°
- B 120°
- C 180°
- D 90°
Explanation: In a perfect tetrahedron, the bond angle is arccos(-1/3) ≈ 109.5°.
Question 11: The bond angle in a trigonal planar molecule is:
- A 120°
- B 109.5°
- C 90°
- D 180°
Explanation: A trigonal planar molecule has three groups arranged in a plane 120° apart.
Question 12: A molecule with a steric number of 5 and one lone pair (like SF₄) has what molecular geometry?
- A See-saw
- B Trigonal bipyramidal
- C Tetrahedral
- D Square planar
Explanation: SF₄ has 4 bonding pairs and 1 lone pair (steric number 5). The lone pair occupies an equatorial position, giving a see-saw (seesaw) molecular geometry.
Question 13: A molecule with a steric number of 6 and two lone pairs (like XeF₄) has what molecular geometry?
- A Square planar
- B Octahedral
- C Tetrahedral
- D See-saw
Explanation: XeF₄ has 4 bonding pairs and 2 lone pairs (steric number 6). The lone pairs occupy opposite (trans) positions, giving a square planar molecular geometry.
Question 14: Which of the following molecules is polar?
- A H₂O
- B CO₂
- C BF₃
- D CH₄
Explanation: H₂O is bent (asymmetric), so the O-H bond dipoles do not cancel and the molecule has a net dipole moment. CO₂, BF₃, and CH₄ are symmetric, so dipoles cancel.
Question 15: Which of the following molecules is nonpolar despite having polar bonds?
- A CO₂
- B H₂O
- C NH₃
- D HCl
Explanation: CO₂ is linear, and the two C=O bond dipoles point in opposite directions and cancel exactly, making the molecule nonpolar.
Question 16: The number of sigma and pi bonds in a molecule of ethene (C₂H₄) is:
- A 5 sigma and 1 pi
- B 4 sigma and 2 pi
- C 6 sigma and 0 pi
- D 4 sigma and 1 pi
Explanation: Ethene has 4 C-H sigma bonds, 1 C-C sigma bond, and 1 C-C pi bond: 5 sigma and 1 pi.
Question 17: The number of sigma and pi bonds in ethyne (C₂H₂) is:
- A 3 sigma and 2 pi
- B 4 sigma and 2 pi
- C 2 sigma and 2 pi
- D 3 sigma and 1 pi
Explanation: Ethyne has 2 C-H sigma bonds, 1 C-C sigma bond, and 2 C-C pi bonds: 3 sigma and 2 pi.
Question 18: Bond length is inversely related to:
- A Bond order
- B Atomic mass
- C Nuclear charge
- D Lone pair count
Explanation: Shorter bonds are stronger. As bond order increases (single → double → triple), bond length decreases and bond strength increases.
Question 19: Which has the shortest carbon-carbon bond?
- A Ethyne (C₂H₂)
- B Ethene (C₂H₄)
- C Ethane (C₂H₆)
- D Benzene (C₆H₆)
Explanation: Bond order determines length: C≡C (triple, ~120 pm) < C=C (double, ~134 pm) < C–C (single, ~154 pm). Ethyne has the shortest bond.
Question 20: Which of the following is an exception to the octet rule?
- A BF₃
- B CH₄
- C H₂O
- D NH₃
Explanation: Boron in BF₃ has only 6 electrons in its valence shell (an incomplete octet). Be, B, and Al frequently have incomplete octets.
Question 21: Which of the following molecules has an expanded octet?
- A SF₆
- B CH₄
- C NH₃
- D H₂O
Explanation: Period 3 and higher elements can use d-orbitals to accommodate more than 8 electrons. SF₆ has 12 electrons around sulfur. CH₄, NH₃, and H₂O all obey the octet rule.
Question 22: The dipole moment of a molecule is a measure of:
- A The net molecular polarity arising from bond dipoles
- B The total number of bonds
- C The strength of a single covalent bond
- D The ionization energy of the central atom
Explanation: Dipole moment (μ = Q × r) measures the net separation of positive and negative charge. It depends on both bond polarity and molecular geometry.
Question 23: Which of the following has the highest bond energy?
- A N₂
- B O₂
- C F₂
- D H₂
Explanation: Triple bonds are the strongest covalent bonds. N≡N in N₂ has a bond energy of ~941 kJ/mol, the highest among the listed species.
Question 24: The bond angle in a linear molecule is:
- A 180°
- B 120°
- C 109.5°
- D 90°
Explanation: A linear molecule has all three atoms in a straight line with a 180° bond angle (e.g., CO₂, BeCl₂, C₂H₂).
Question 25: The percent ionic character of a bond can be estimated using:
- A Pauling's electronegativity difference formula
- B The ideal gas law
- C Hess's law
- D The Henderson-Hasselbalch equation
Explanation: Pauling's equation: % ionic character ≈ (1 − e^(−(ΔEN)²/4)) × 100%, based on the electronegativity difference between the bonded atoms.