Explain why elements in Group 1 of the periodic table become more reactive as you go down the group.

AQA A-Level Chemistry (7405) — 3.2.1 Periodicity · Explain · 5 marks · View as Markdown

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

Group 1 elements are known as the alkali metals. They all react with water, but the vigour of the reaction increases 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 have more electron shells, so the outer electron is further from the nucleus. There is increased shielding from the additional inner electrons, which reduces the effective nuclear charge on the outer electron. Consequently the electrostatic attraction between the nucleus and the outer electron decreases, making it easier to lose that electron. Therefore the atoms become more reactive down the group.

Examiner tips

  • Use the sequence: loss of one electron → more shells → shielding → weaker attraction → easier loss → higher reactivity.
  • Mention the role of effective nuclear charge and the distance of the valence electron from the nucleus.

Mark scheme (5 marks)

  1. Group 1 atoms react by losing one outer electron
  2. As you go down the group, the atoms have more electron shells / the outer electron is further from the nucleus
  3. There is increased shielding / more inner electrons shield the outer electron from the nucleus
  4. The electrostatic attraction between the nucleus and the outer electron decreases
  5. Therefore the outer electron is lost more easily, making the atom more reactive

Key terms in this question

Group 1

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