AQA A-Level Chemistry Paper 3, 2023: Question 9

1 mark · Easy difficulty · Multiple Choice

Substance with Significant Electron Delocalisation This question tests the identification of a substance exhibiting significant electron delocalisation, such as in a structure with conjugated π-bonds or a lattice of delocalised electrons.

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Question

AQA A-Level Chemistry Paper 3, 2023: Question 9
Question text

09 Which substance has significant electron delocalisation?

[1 mark]

A graphite

B iodine

C sodium chloride

D tetrachloromethane

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2023: Question 9

09 A 1 (AO1) graphite

How to answer it

Identifying Substances with Significant Electron Delocalisation

Question

Which substance has significant electron delocalisation?

  • A: Graphite
  • B: Iodine
  • C: Sodium chloride
  • D: Tetrachloromethane

Correct Answer: A (Graphite)

Graphite has significant electron delocalisation because its structure consists of layers of carbon atoms arranged in a hexagonal pattern. Each carbon atom forms three sigma bonds, leaving one electron in a p orbital. These electrons are delocalised across the layer, allowing for electron mobility.

Teacher Tip: Electron delocalisation occurs in systems with conjugated double bonds or when π-electrons are shared across a structure, as in graphite's hexagonal sheets.

Explanation of Other Options

  • B: Iodine - Iodine forms simple covalent molecules with no delocalised electrons.
  • C: Sodium chloride - Sodium chloride is an ionic compound with localised electrons in its lattice structure.
  • D: Tetrachloromethane - Tetrachloromethane (CCl4) is a covalent compound with no delocalised electrons, as all bonds are sigma bonds.
Teacher Tip: Focus on structures that exhibit conjugation or overlapping p orbitals to identify delocalised systems.

Why Graphite is the Best Answer

The delocalised electrons in graphite allow it to conduct electricity and make it an ideal lubricant because the layers can slide over each other. This property is directly related to its electron delocalisation.

Graphite is the only option with significant delocalisation of electrons.

Topics

Physical Chemistry · 3.1.3 Bonding

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.