Explain why elements in Group 1 of the periodic table become more reactive as you go down the group. In your answer, refer to atomic structure and the loss of electrons.

Edexcel A-Level Chemistry (9CH0) — Topic 2 Inorganic chemistry and the Periodic Table · Explain · 5 marks · View as Markdown

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

Group 1 elements, known as the alkali metals, are all reactive metals that react vigorously with water. Their reactivity changes as you move down the group from lithium to caesium.

Model answer (5 marks)

Group 1 atoms react by losing one outer electron.

As you go down the group the atoms get larger and have more electron shells.

The outer electron is further from the nucleus as you go down the group.

There is more shielding of the outer electron by inner shells of electrons.

The outer electron is lost more easily, so reactivity increases down the group.

Examiner tips

  • Use the word ‘reactive’ and mention ‘loss of one outer electron’ to show understanding of the reaction mechanism.
  • Show the trend of increasing atomic radius and shielding to justify why the outer electron is easier to remove.
  • Keep the answer concise – one sentence per point – to fit the 5‑mark allocation.

Common mistakes

  • Confusing the trend with the opposite (e.g., saying reactivity decreases down the group).
  • Failing to mention the role of shielding or atomic size in making the outer electron easier to lose.
  • Using vague language such as ‘more reactive’ without explaining the underlying atomic structure.

Mark scheme (5 marks)

  1. Group 1 atoms react by losing one outer electron
  2. As you go down the group, the atoms get larger / have more electron shells
  3. The outer electron is further from the nucleus as you go down the group
  4. There is more shielding of the outer electron by inner shells of electrons
  5. The outer electron is lost more easily, so reactivity increases down the group

Key terms in this question

Group 1

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