Magnesium has an atomic number of 12 and a mass number of 24. Describe the structure of a magnesium atom, including the number and location of each type of subatomic particle.

Eduqas GCSE Chemistry — 2.1 Bonding, structure and properties · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Magnesium has 12 protons in the nucleus.
Magnesium has 12 neutrons in the nucleus.
Magnesium has 12 electrons.
The electrons are found in shells (energy levels) surrounding the nucleus.

Examiner tips

  • Use the exact wording ‘protons in the nucleus’, ‘neutrons in the nucleus’, ‘electrons in shells’ to match the mark scheme.
  • Count correctly: 12 of each particle.
  • Mention that the electrons orbit the nucleus in energy levels.

Common mistakes

  • Writing the wrong number of protons, neutrons or electrons.
  • Forgetting to specify that electrons are in shells.
  • Using vague terms like ‘around the nucleus’ instead of ‘in shells’.

Mark scheme (4 marks)

  1. Magnesium has 12 protons (located) in the nucleus
  2. Magnesium has 12 neutrons (located) in the nucleus
  3. Magnesium has 12 electrons
  4. Electrons are found in shells / energy levels surrounding / orbiting the nucleus

Key terms in this question

atomic number · mass number

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