Magnesium oxide is an ionic compound. Explain how magnesium oxide is formed when magnesium reacts with oxygen, including how the ions achieve a stable electronic structure.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Magnesium (atomic number 12) reacts vigorously with oxygen to form magnesium oxide, an ionic compound used as a refractory material in furnaces.
Model answer (4 marks)
Magnesium loses two 3s electrons to give a Mg²⁺ ion, giving it the electron configuration of neon. Oxygen gains two 2p electrons to give an O²⁻ ion, giving it the electron configuration of neon. Both ions now have a full outer shell and a stable electronic structure. The oppositely charged ions are attracted electrostatically, forming the ionic compound MgO.
Examiner tips
- Use the word ‘lose’ for Mg and ‘gain’ for O to show electron transfer.
- Mention the noble‑gas configuration to justify stability.
- Show the charge of each ion (Mg²⁺, O²⁻).
- Explain that the attraction between opposite charges gives the ionic bond.
Common mistakes
- Writing Mg as Mg⁺ or O as O⁻ instead of Mg²⁺ and O²⁻.
- Failing to state that both ions achieve a noble‑gas configuration.
- Omitting the electrostatic attraction that holds the ions together.
Mark scheme (4 marks)
- Magnesium atom loses 2 electrons to form a Mg²⁺ ion
- Oxygen atom gains 2 electrons to form an O²⁻ ion
- Both ions achieve a full outer shell / stable electronic structure (like a noble gas)
- The oppositely charged ions are held together by electrostatic attraction to form the ionic compound
Key terms in this question
ionic compound · ion · electronic structure
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →