Calcium and magnesium are both Group 2 metals. Explain why calcium is a more reactive metal than magnesium, and describe what you would observe when a small piece of calcium is added to cold water.

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 water to form metal hydroxides and hydrogen gas. Their reactivity increases down the group.

Model answer (5 marks)

Calcium has more electron shells than magnesium, so its outermost electrons are in a higher energy level and are further from the nucleus. Consequently the attraction between the nucleus and the outer electrons is weaker, making it easier for calcium to lose its two valence electrons and form Ca²⁺. Thus calcium is more reactive than magnesium.

When a small piece of calcium is added to cold water, it reacts rapidly, producing hydrogen gas:
Ca + 2 H₂O → Ca(OH)₂ + H₂↑
Effervescence is seen as bubbles of hydrogen gas. The calcium dissolves, leaving a milky, cloudy solution of calcium hydroxide, which only partly dissolves in water.

Examiner tips

  • Use the word ‘more reactive’ and explain the electronic reason (more shells, weaker attraction).
  • Show the reaction equation and describe effervescence and the milky solution.

Mark scheme (5 marks)

  1. Calcium has more electron shells / energy levels than magnesium
  2. The outer electron in calcium is further from the nucleus / less strongly attracted to the nucleus
  3. Calcium loses its outer electron(s) more easily, so it forms cations more readily
  4. Effervescence / bubbles of hydrogen gas are seen (when calcium is added to water)
  5. The calcium dissolves / disappears and the solution turns cloudy / milky (calcium hydroxide partially dissolves)

Key terms in this question

Group 2

Related

More Group 2 metals questions

▶ Try answering this question with AI marking (free) →