Describe the trends in reactivity and the nature of the oxides as you descend Group 2 of the periodic table. Explain why reactivity changes down the group.

AQA A-Level Chemistry (7405) — 3.2.2 Group 2, the alkaline earth metals · Describe · 5 marks · View as Markdown

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

Group 2 elements are known as the alkaline earth metals. They include beryllium, magnesium, calcium, strontium and barium.

Model answer (5 marks)

Reactivity increases down Group 2 because the atoms become larger; the outer 2s electrons are further from the nucleus and are shielded by more inner electrons. Consequently the ionisation energy decreases, making it easier to lose the two valence electrons and form the M²⁺ ion. The oxides of Group 2 metals are basic; they dissolve in water to give alkaline solutions (e.g. Mg(OH)₂, Ca(OH)₂).

Examiner tips

  • Use the word ‘increases’ for reactivity trend; mention size, shielding and ionisation energy; state that oxides are basic and give an example.
  • Show the link between larger radius, lower ionisation energy and easier loss of electrons.

Mark scheme (5 marks)

  1. Reactivity increases down Group 2
  2. Atoms get larger / atomic radius increases down the group, so outer electrons are further from the nucleus
  3. Increased shielding / shielding effect increases down the group
  4. Outer electrons are lost more easily / ionisation energy decreases down the group
  5. Group 2 oxides are basic / dissolve in water to form alkaline solutions

Key terms in this question

reactivity

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