Sodium, potassium and lithium are all elements in Group 1 of the periodic table. Explain why these elements become more reactive going down the group.

WJEC A-Level Chemistry (Wales) — 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).

Group 1 metals all react vigorously with water to produce a metal hydroxide and hydrogen gas. Lithium reacts steadily, sodium reacts rapidly, and potassium reacts so vigorously that the hydrogen gas produced ignites.

Model answer (5 marks)

1. Atoms in Group 1 have an increasing number of electron shells as you move down the group.
2. The outermost electron is therefore further from the nucleus in potassium than in sodium and further still in lithium.
3. This greater distance reduces the electrostatic attraction between the nucleus and the outer electron.
4. Consequently the outer electron is lost more easily in potassium than in sodium and in sodium than in lithium.
5. Because Group 1 metals react by losing this outer electron, the ease of loss determines reactivity, so reactivity increases down the group.

Examiner tips

  • Use the exact terms: "electron shells", "outer electron", "electrostatic attraction", "lost more easily".
  • Show the logical progression: shells → distance → attraction → loss → reactivity.
  • Keep each point short and directly linked to the mark scheme.

Common mistakes

  • Confusing the trend for Group 2 or 7 metals.
  • Using the word "gain" instead of "lose" for the outer electron.
  • Omitting the link between loss of the outer electron and reactivity.

Mark scheme (5 marks)

  1. Going down Group 1, the atoms have more electron shells
  2. The outer electron is further from the nucleus going down the group
  3. The attraction between the nucleus and the outer electron decreases going down the group
  4. The outer electron is lost more easily going down the group
  5. Because Group 1 metals react by losing their outer electron, the ease of losing this electron determines reactivity — so reactivity increases down the group

Key terms in this question

Group 1

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