Magnesium reacts with oxygen to form magnesium oxide. Explain, in terms of electrons, what happens to the magnesium and oxygen atoms during this reaction, and state the type of bonding present in magnesium oxide.

Edexcel A-Level Chemistry (9CH0) — Topic 1 Foundations in chemistry · Explain · 5 marks · View as Markdown

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

Magnesium burns in oxygen to form a white solid, magnesium oxide. The formula of magnesium oxide is MgO.

Model answer (5 marks)

Magnesium loses two electrons to give a Mg²⁺ ion.
Oxygen gains two electrons to give an O²⁻ ion.
Both ions now have a full outer shell and a stable electron configuration.
The oppositely charged ions are attracted to each other.
The bonding in MgO is ionic.

Examiner tips

  • Use the exact terms Mg²⁺ and O²⁻; mention electron loss/gain. Show the stable configuration (full outer shell). State ionic bonding explicitly.
  • common_mistakes
  • :
  • Writing ‘magnesium gives up two electrons’ without specifying Mg²⁺. Forgetting to mention the full outer shell. Saying ‘covalent bonding’ instead of ionic.

Mark scheme (5 marks)

  1. Magnesium atom loses 2 electrons (to form Mg²⁺ ion)
  2. Oxygen atom gains 2 electrons (to form O²⁻ ion)
  3. Both ions formed have a full outer shell / achieve a stable electron configuration
  4. Oppositely charged ions are formed (Mg²⁺ and O²⁻)
  5. The type of bonding in magnesium oxide is ionic bonding

Key terms in this question

ion

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