Lithium, sodium and potassium are all elements in Group 1 of the periodic table. Explain why these three elements have similar chemical properties, and why their reactivity increases going down the group.

Eduqas A-Level Chemistry — 2.2 Group 1, 2 and 7 · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Elements in the same group have the same number of electrons in their outer shell, giving them similar chemical properties. Going down the group each element has more electron shells, so the outer electron is held less strongly by the nucleus and is more easily lost. Therefore reactivity increases down the group because the outer electron is lost more readily.

Examiner tips

  • Use the command word "explain" – describe the cause and effect, not just state facts.
  • Mention the outer‑shell electron count and the shielding effect explicitly.
  • Show the link between weaker attraction and increased reactivity.
  • Keep the answer concise – 5 marks, so one or two short sentences are enough.

Common mistakes

  • Failing to mention the outer‑shell electron count or shielding effect.
  • Giving a general statement about reactivity without linking it to electron loss.
  • Using vague language such as "more reactive" without explaining why.

Mark scheme (5 marks)

  1. Elements in the same group have the same number of electrons in their outer shell
  2. This gives them similar chemical properties
  3. Going down the group, each element has more electron shells
  4. The outer electron is held less strongly by the nucleus / is more easily lost
  5. Therefore reactivity increases down the group because the outer electron is lost more readily

Key terms in this question

Group · reactivity

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