Chemical bonding MCQs
MDCAT · Chemistry · 6 questions
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Revision summary
PMDC MDCAT syllabus: Chemical bonding
Atoms bond to reach a stable arrangement of electrons. Ionic bonds form by electron transfer between atoms with a large electronegativity difference (NaCl). Covalent bonds share pairs; in a coordinate (dative) bond both electrons come from one atom (NH₄⁺, H₃O⁺). Shapes follow VSEPR: electron pairs around the central atom push apart, and lone pairs push harder than bond pairs. Four bond pairs give a tetrahedron at 109.5° (CH₄, sp³); three bond pairs and one lone pair give a pyramid at about 107° (NH₃); two bond pairs and two lone pairs give a bent shape at about 104.5° (H₂O). Three bond pairs and no lone pair give a trigonal plane at 120° (BF₃, sp²), and two give a straight line at 180° (CO₂, BeCl₂, sp). In ethene each carbon is sp² with one σ and one π bond between the carbons; in ethyne each is sp with one σ and two π bonds.
Questions with answers
Written by Parcha from the syllabus. Samples until a subject reviewer checks them; report anything wrong from the practice screen.
Q1 · Parcha original · Sample
The shape of a methane (CH₄) molecule is:
- A. Tetrahedral
- B. Square planar
- C. Trigonal planar
- D. Linear
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Answer: A. Tetrahedral
Carbon in methane has four bond pairs and no lone pairs, so the pairs point to the corners of a tetrahedron with H–C–H angles of 109.5°. The carbon is sp³ hybridised.
Open this question on its own pageQ2 · Parcha original · Sample
The H–O–H bond angle in a water molecule is about:
- A. 109.5°
- B. 120°
- C. 104.5°
- D. 180°
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Answer: C. 104.5°
Oxygen has two bond pairs and two lone pairs. Lone pairs repel more strongly than bond pairs and squeeze the bond angle from 109.5° down to about 104.5°, giving a bent shape.
Q3 · Parcha original · Sample
Each carbon atom in ethene (C₂H₄) is:
- A. sp hybridised
- B. sp² hybridised
- C. sp³ hybridised
- D. Not hybridised
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Answer: B. sp² hybridised
Each carbon forms three σ bonds (two to H, one to C) using sp² orbitals at 120°, and the unhybridised p orbitals overlap side by side to form the π bond of C=C.
Q4 · Parcha original · Sample
The bond in solid sodium chloride is:
- A. Covalent
- B. Metallic
- C. Hydrogen
- D. Ionic
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Answer: D. Ionic
Sodium gives its outer electron to chlorine, forming Na⁺ and Cl⁻ ions held in a lattice by electrostatic attraction: an ionic bond. The large electronegativity difference favours electron transfer.
Q5 · Parcha original · Sample
A coordinate covalent (dative) bond is present in:
- A. CH₄
- B. NH₄⁺
- C. H₂O
- D. Cl₂
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Answer: B. NH₄⁺
In the ammonium ion, nitrogen's lone pair is donated to an H⁺ ion, so both electrons of that N–H bond come from nitrogen: a coordinate bond. Once formed, all four N–H bonds are identical.
Q6 · Parcha original · Sample
The shape of a boron trifluoride (BF₃) molecule is:
- A. Pyramidal
- B. Tetrahedral
- C. Trigonal planar
- D. Bent
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Answer: C. Trigonal planar
Boron has three bond pairs and no lone pair, so the three B–F bonds lie in one plane at 120° (sp²). Ammonia, with a lone pair, is pyramidal instead.