OCR A-Level Chemistry AS Breadth in chemistry (01), June 2019: Question 14

1 mark · Easy difficulty · Multiple Choice

Identify the correct description of the bonding between carbon atoms in an ethene molecule.

Practise this question

Question

Multiple choice question 14 asking for the best description of the bonding between carbon atoms in an ethene molecule. Options are A: One sigma-bond and one pi-bond, B: One pi-bond, C: Two sigma-bonds, D: Two pi-bonds. An answer box is provided at the bottom with a [1] mark allocation.
Question text

14 What is the best description for the bonding between the carbon atoms in an ethene molecule?

A One σ-bond and one π-bond

B One π-bond

C Two σ-bonds

D Two π-bonds

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 14 is A, worth 1 mark under assessment objective AO1.1.

14 A 1 AO1.1

How to answer it

Bonding in Ethene

What this question tests

This question assesses your fundamental knowledge of covalent bonding types (AO1.1), specifically how single and multiple covalent bonds are formed between carbon atoms in alkenes through the overlap of atomic orbitals to form sigma (σ) and pi (π) bonds.

Question 14

Exam Breakdown

✅ Correct Answer

A — One σ-bond and one π-bond

💡 Key Knowledge

  • Single covalent bond: Formed by the end-on (linear) overlap of atomic orbitals, creating a σ -bond with electron density concentrated directly between the nuclei.
  • Double covalent bond: Consists of one σ -bond and one π -bond.
  • π -bond: Formed by the sideways (parallel) overlap of adjacent p-orbitals above and below the bonding nuclear axis.
  • Ethene structure: Contains a C=C double bond, meaning it has one σ -bond and one π -bond between the two carbon atoms (along with σ -bonds to the hydrogen atoms).

🧠 Exam Technique

For multiple-choice questions involving bonding types, quickly recall the rule of multiple bonds: a single bond is always one σ -bond; a double bond is one σ -bond and one π -bond; a triple bond is one σ -bond and two π -bonds. Do not let complex orbital terminology distract you from this core rule!

❌ Common Errors

  • Assuming a double bond means two identical bonds (e.g., choosing C or D).
  • Forgetting that a double bond always requires a foundational σ -bond before a π -bond can form sideways.
Mark Scheme Allocation: 1 mark for selecting option A (AO1.1).

Topics

Module 2: Foundations in chemistry · Module 4: Core organic chemistry · 2.2 Electrons, bonding and structure · 4.1 Basic concepts and hydrocarbons

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.