48 exam-style questions on The covalent model — topic S2.2 of Structure 2: Models of bonding and structure in the IB Chemistry syllabus — with answers and explanations. Samples below; the full set is free with an account.
What is the shape of a carbon dioxide (CO₂) molecule?
Answer: linear
The central carbon has two double bonds and no lone pairs; the two regions of electron density repel to opposite sides, giving a linear O=C=O with a 180° bond angle.
What is the approximate H–N–H bond angle in an ammonia (NH₃) molecule?
Answer: 107°
Ammonia has three bonding pairs and one lone pair. The lone pair repels more strongly, compressing the bond angle from 109.5° to about 107° (trigonal pyramidal).
Determine the number of lone pairs on the central sulfur atom in a sulfur dioxide (SO2) molecule.
Answer: 1
In SO₂ the central S has two bonding regions and one lone pair, giving a bent (V-shaped) molecule.
State the number of sigma (σ) and pi (π) bonds in a molecule of ethyne, C2H2 (H–C≡C–H).
Answer: 3 σ and 2 π
Two C–H single bonds (2 σ) plus a C≡C triple bond (1 σ + 2 π) give 3 σ and 2 π bonds in total.
Which species has a trigonal planar electron domain geometry around the central atom?
Answer: BF3
BF₃ has three bonding pairs and no lone pairs on boron, giving trigonal planar geometry with 120° angles.
In the Lewis (electron dot) structure of ammonia, NH₃, state the number of bonding pairs and lone pairs on the nitrogen atom.
Answer: Three bonding pairs and one lone pair
Nitrogen has five valence electrons; three are shared with hydrogen atoms and the remaining two stay as one lone pair, giving four electron domains in total. The commonest error is to count only the bonds and forget that every unshared pair must still be drawn.
That was 6 of 48 The covalent model questions.
Practise all 48 freeStateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
DeduceAO2 · 1–4 marks
Reach the conclusion from the information given, showing the chain of reasoning.
ListAO1 · 1–2 marks
Give the items only, one per line. Extra description earns nothing and costs time.
48 The covalent model questions — free with an account. Spaced repetition, streaks and full exam simulations included.
Practise them freeThis platform is independently developed and is not endorsed by, affiliated with, or sponsored by the International Baccalaureate Organization. “International Baccalaureate” and “IB” are registered trademarks of the IBO.