Edexcel A-Level Chemistry AS Paper 2, June 2017: Question 2

1 mark · Easy difficulty · Multiple Choice

Identify which of the given molecules has a linear shape.

Practise this question

Question

Multiple-choice question asking which molecule has a linear shape, with four options: A (H2S), B (SO2), C (CO2), and D (CH2=CH2). Total for the question is 1 mark.
Question text

2 Which molecule has a linear shape?

A H2S

B SO2

C CO2

D CH2 CH2

(Total for Question 2 = 1 mark)

Mark scheme

Show the mark scheme Mark scheme stating that the only correct answer is C, with explanations for why A, B, and D are incorrect.

Question

Answer Mark

Number

2 2. The only correct answer is C (1)

A is not correct because it has a similar shape to water.

B is not correct because it has a trigonal planar shape; resulting from the lone pair and two

groups of electrons in the two double bonds.

D is not correct because it is planar but not linear.

(Total for Question 2 = 1 mark)

How to answer it

Identifying Molecular Shapes (Linear Molecules)

Edexcel AS Level Chemistry • Multiple Choice • 1 Mark

What this question tests

This question assesses your understanding of Valence Shell Electron Pair Repulsion (VSEPR) theory. You need to determine the shapes of simple molecules and ions by counting bonding pairs and lone pairs around the central atom, understanding how electron pairs repel each other to maximise separation.

Question Analysis (Multiple Choice)

Which molecule has a linear shape?

✅ Correct Answer: C (CO₂)

Carbon dioxide ( CO₂ ) has a central carbon atom bonded to two oxygen atoms via double bonds. With 2 regions of electron density and 0 lone pairs, the bonds push as far apart as possible, giving a linear shape with a bond angle of 180°.

💡 Key Knowledge

  • VSEPR Theory: Electron pairs repel each other and arrange themselves as far apart in space as possible.
  • Double bonds: Count as a single region of electron density/charge cloud when predicting shape.
  • Linear geometry: Occurs when there are 2 bonding pairs and 0 lone pairs around the central atom.

🧠 Exam Technique

Always quickly sketch or mentally visualise the dot-and-cross diagram or structure for each option in multiple-choice shape questions before locking in your answer!

❌ Common Errors & Distractor Analysis

  • A ( H₂S ): Sulfur has 2 bonding pairs and 2 lone pairs (bent/nonlinear shape, similar to water).
  • B ( SO₂ ): Sulfur has 2 regions of electron density from double bonds plus 1 lone pair, resulting in a bent shape.
  • D ( CH₂=CH₂ ): Ethene has a planar (trigonal planar around each carbon), but not linear structure due to multiple bond centres.
Mark Allocation: 1 mark is awarded for selecting option C. No working out required, but mental elimination of incorrect VSEPR geometries is essential.

Topics

Physical Chemistry · Topic 2: Bonding and Structure

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 2, June 2017. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.