Beryllium (Be), magnesium (Mg), calcium (Ca) and barium (Ba) are all Group 2 metals. Each metal reacts with dilute hydrochloric acid to form a metal chloride and hydrogen gas. Using your knowledge of the reactivity series and Group 2 trends, explain why barium reacts more vigorously with dilute hydrochloric acid than magnesium does, and predict what you would observe during the reaction of barium with dilute hydrochloric acid.

Edexcel A-Level Chemistry (9CH0) — 4.1 Group 2 metals · Explain · 5 marks · View as Markdown

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

Group 2 metals react with dilute hydrochloric acid. The reactivity of Group 2 metals increases down the group.

Model answer (5 marks)

Barium is lower in Group 2 than magnesium, so it has more electron shells and its outermost electron is in a higher‑energy, more distant shell. The increased shielding and weaker nuclear attraction mean the outer electron is easier to lose, requiring less energy to remove it. Consequently barium is higher in the reactivity series than magnesium and reacts more vigorously with dilute HCl. In the reaction of barium with dilute HCl you would observe rapid, vigorous effervescence as hydrogen gas is produced and the barium dissolves quickly.

Examiner tips

  • Mention the position in the group and the number of shells to justify reactivity
  • Explain the effect of shielding and nuclear attraction on the outer electron
  • State that barium is higher in the reactivity series than magnesium
  • Describe the observation: rapid bubbles, fast dissolution

Common mistakes

  • Confusing magnesium with barium in terms of position in the group
  • Failing to explain why the outer electron is easier to lose
  • Giving a vague observation such as "some gas" instead of "rapid effervescence"

Mark scheme (5 marks)

  1. Barium is lower/further down Group 2 than magnesium
  2. Barium atoms have more electron shells / the outer electron is in a higher energy shell / the outer electron is further from the nucleus
  3. The outer electron is more easily lost / less energy is needed to remove the outer electron (because there is greater shielding / weaker nuclear attraction on the outer electron)
  4. Barium is higher in the reactivity series than magnesium / barium is more reactive than magnesium
  5. A correct observation for barium reacting with dilute hydrochloric acid: e.g. bubbles/effervescence produced rapidly / barium dissolves quickly / the reaction is faster/more vigorous than magnesium

Key terms in this question

reactivity series · Group 2

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