Iron has two common isotopes: iron-56 and iron-54. State what is meant by the term isotope and describe the differences in the subatomic particles found in an atom of iron-56 compared to an atom of iron-54.

Eduqas A-Level Chemistry — 2.3 Transition metals (A-Level only) · State · 5 marks · View as Markdown

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

Iron is an element with atomic number 26. It has several naturally occurring isotopes, the most abundant being iron-56.

Model answer (5 marks)

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.

Iron‑56 and iron‑54 both have 26 protons.

Iron‑56 has 30 neutrons, whereas iron‑54 has 28 neutrons.

Both isotopes have 26 electrons, so the overall charge is zero.

Examiner tips

  • Use the definition of isotope first. Show the proton count is the same. State the neutron difference. Mention the electron count to show neutrality.

Common mistakes

  • Confusing the isotope mass number with neutron count. Forgetting to note the equal electron number. Mixing up the neutron numbers of the two isotopes.

Mark scheme (5 marks)

  1. Isotopes are atoms of the same element with the same number of protons but a different number of neutrons.
  2. Both iron-56 and iron-54 have the same number of protons (26 protons each).
  3. Iron-56 has more neutrons than iron-54 (30 neutrons compared to 28 neutrons).
  4. Both isotopes have the same number of electrons (26 electrons each), as the overall charge of an atom is zero.

Key terms in this question

isotope

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