An atom of element X has an atomic number of 11 and a mass number of 23. State the number of protons, neutrons, and electrons in a neutral atom of element X, and name the element.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.2 Atoms · State · 4 marks · View as Markdown

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

Model answer (4 marks)

Protons: 11
Neutrons: 12
Electrons: 11
Element: Sodium (Na)

Examiner tips

  • State each number separately; include the element’s symbol in brackets.
  • Use the formula neutrons = mass number – atomic number to calculate neutrons.
  • Remember a neutral atom has equal protons and electrons.
  • Write the element name in full and the symbol in parentheses.

Common mistakes

  • Calculating neutrons incorrectly (e.g. 23‑11=11 instead of 12).
  • Forgetting to state the element name or symbol.
  • Mixing up the number of electrons with the atomic number in a neutral atom.

Mark scheme (4 marks)

  1. 11 protons
  2. 12 neutrons (mass number − atomic number = 23 − 11)
  3. 11 electrons (equal to the number of protons in a neutral atom)
  4. Sodium (Na)

Key terms in this question

atomic number · mass number · electron · atom

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