Sodium has the atomic number 11 and a relative atomic mass of approximately 23. State the number of protons, neutrons and electrons in a neutral sodium atom, and use these values to explain why sodium is electrically neutral.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.3 Atomic structure · State and Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Sodium has 11 protons.
Sodium has 12 neutrons.
Sodium has 11 electrons.
The atom is electrically neutral because the number of negatively charged electrons equals the number of positively charged protons, so the charges cancel out.

Examiner tips

  • Use the exact numbers (11 protons, 12 neutrons, 11 electrons).
  • Show the equality of electrons and protons to justify neutrality.
  • Keep the explanation concise and directly linked to charge balance.

Common mistakes

  • Confusing the number of neutrons with the atomic mass (e.g. writing 23 neutrons).
  • Forgetting to state that the atom is neutral because electrons = protons.
  • Using vague language such as 'balanced' without specifying charges.

Mark scheme (4 marks)

  1. Sodium has 11 protons
  2. Sodium has 12 neutrons
  3. Sodium has 11 electrons (equal to the number of protons)
  4. The atom is electrically neutral because the number of (negatively charged) electrons equals the number of (positively charged) protons, so the charges cancel / balance out

Key terms in this question

atomic number · electron · neutron · proton

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