Explain why magnesium has a high melting point and can conduct electricity.

AQA A-Level Chemistry (7405) — 3.1.3 Bonding · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Magnesium is a metal used in lightweight alloys. It is solid at room temperature and melts at 650 °C.

Model answer (5 marks)

Magnesium is a metallic element that forms a crystal lattice of Mg²⁺ ions.
The lattice is surrounded by a sea of delocalised electrons.
Strong electrostatic attractions exist between the positive ions and the delocalised electrons.
A large amount of energy is required to break these attractions, giving magnesium a high melting point.
The delocalised electrons can move freely through the lattice, allowing the metal to conduct electricity.

Examiner tips

  • Use the term "metallic bond" and "sea of delocalised electrons" to show understanding of bonding.
  • Explain that the high melting point is due to the strong ion–electron attractions.
  • Show that electrical conductivity comes from the mobility of the delocalised electrons.
  • Keep the answer concise and directly linked to the points in the scheme.

Common mistakes

  • Confusing the lattice with a covalent network; magnesium is not covalent.
  • Failing to mention the delocalised electrons as the reason for conductivity.
  • Using vague terms like "strong bonds" without specifying electrostatic attraction.

Mark scheme (5 marks)

  1. Magnesium consists of a lattice/regular arrangement of positive ions (Mg²⁺ ions)
  2. Surrounded by/in a sea of delocalised electrons
  3. There are strong electrostatic attractions between the positive ions and the delocalised electrons
  4. A lot of energy is needed to overcome these strong attractions, so the melting point is high
  5. The delocalised electrons can move through the structure and carry charge, so magnesium conducts electricity

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