A neutral atom of carbon-14 has a mass number of 14 and an atomic number of 6. State the number of protons, neutrons, and electrons in this atom, and explain why carbon-14 is described as an isotope of carbon-12.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The atom has 6 protons, 8 neutrons and 6 electrons.
Carbon‑14 is an isotope of carbon‑12 because both have the same number of protons (atomic number 6) but different numbers of neutrons, giving different mass numbers (14 vs 12).
Carbon‑14 is an isotope of carbon‑12 because both have the same number of protons (atomic number 6) but different numbers of neutrons, giving different mass numbers (14 vs 12).
Examiner tips
- State the numbers first, then give the isotope explanation; use the term ‘isotope’ and mention same protons, different neutrons.
- Show the calculation of neutrons: 14−6=8.
- Use the word ‘neutral’ to justify equal electrons and protons.
- Keep the answer concise – 4 marks only.
Mark scheme (4 marks)
- The atom contains 6 protons
- The atom contains 8 neutrons
- The atom contains 6 electrons (because it is neutral / electrons equal protons in a neutral atom)
- Carbon-14 and carbon-12 have the same number of protons / same atomic number but different numbers of neutrons / different mass numbers
Key terms in this question
mass number · atomic number · neutrons · protons · electrons
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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