Magnesium burns in oxygen to form magnesium oxide. The word equation for this reaction is: magnesium + oxygen → magnesium oxide. Explain what is meant by the terms 'element' and 'compound', and state which substances in this reaction are elements and which is a compound.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.5 Chemical formulae, equations and calculations · Explain · 4 marks · View as Markdown

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

Magnesium burns in oxygen to form magnesium oxide. The word equation for this reaction is: magnesium + oxygen → magnesium oxide.

Model answer (4 marks)

An element is a substance that consists of only one type of atom.
Magnesium and oxygen are both elements.
A compound is a substance made up of two or more different types of atoms chemically combined.
Magnesium oxide is the compound.

Examiner tips

  • Use the exact definitions given in the mark scheme.
  • State both magnesium and oxygen as elements.
  • Mention magnesium oxide as the compound.
  • Keep the answer concise and to the point.

Common mistakes

  • Saying only magnesium is an element and forgetting oxygen.
  • Describing magnesium oxide as an element instead of a compound.
  • Using vague terms like "made of atoms" without specifying one or more types.

Mark scheme (4 marks)

  1. An element is a substance made up of only one type of atom
  2. Magnesium and oxygen are both elements (both must be stated for the mark)
  3. A compound is a substance made up of two or more types of atoms chemically combined together
  4. Magnesium oxide is the compound

Key terms in this question

element · compound

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