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Learn7405Paper 1 · Paper 1: Physical and inorganic chemistryGroup 2, the alkaline earth metalsGroup 2 reactions and trends
Group 2, the alkaline earth metals · Subtopic 1 of 2

Group 2

Down group 2, atomic radius increases, first ionisation energy decreases, so reactivity increases. The metals react with water: Mg slowly (fast with steam to MgO + H₂), Ca–Ba readily to give hydroxide + H₂, e.g. Ca+2H2O→Ca(OH)2+H2\mathrm{Ca+2H_2O\rightarrow Ca(OH)_2+H_2}. Hydroxides become more soluble down the group (Mg(OH)₂ sparingly, Ba(OH)₂ soluble), so solutions become more alkaline. Sulfates become less soluble (BaSO₄ insoluble: used to test for sulfate and in barium meals). Uses: Ca(OH)₂ and CaCO₃ neutralise acid soils; Mg(OH)₂ in antacids.

Cambridge 9701 Paper 1Cambridge 9701 Paper 2Edexcel YCH11 WCH12AQA 7405 Paper 1≈ 45 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Describe and explain trends in group 2.
  • Write equations for reactions with oxygen, water and acids.
  • Describe trends in solubility of hydroxides and sulfates.
  • Describe uses of group 2 compounds.
Pause and think

Doctors give patients a "barium meal" before X-rays, but barium ions are poisonous. Why is it safe?

Section 2 of 14

Core idea

Start hereFrom fireworks to farming

Group 2 compounds colour fireworks red and green, neutralise acid soils and make X-rays of your gut possible.

The big idea

Down group 2, outer electrons are lost more easily, so reactivity increases. Hydroxides get more soluble; sulfates get less soluble.

1. Reactions with water

Group 2 with water

Reactivity increases down the group.

Worked exampleNeutralising acidic soil

A field needs 5.0 kg of CaCO₃ to neutralise its acid. How many moles of H⁺ does this neutralise? (CaCO3+2H+→Ca2++H2O+CO2\mathrm{CaCO_3+2H^+\rightarrow Ca^{2+}+H_2O+CO_2})

Goal
Moles of H⁺.
Strategy
Moles of CaCO₃, ratio 1 : 2.
  1. n(CaCO3)=5000100=50 moln(\mathrm{CaCO_3})=\frac{5000}{100}=50\ \text{mol}
    Mr=100M_r=100.
  2. n(H+)=100 moln(\mathrm{H^+})=100\ \text{mol}
    Ratio 1 : 2.
Answer100 mol of H⁺.
✓ CheckEach carbonate removes two H⁺ ✓.
Key takeawaySolubility trends Mg(OH)₂ sparingly soluble → Ba(OH)₂ soluble. MgSO₄ soluble → BaSO₄ insoluble.
Pause and think

Why does the reaction of calcium with dilute sulfuric acid slow down quickly?

Summary

  • Reactivity ↑ down.
  • Hydroxides ↑, sulfates ↓ solubility.
  • Uses: soils, antacids, BaSO₄.
Key words
Alkaline earth metal
Group 2 element.
Thermal decomposition
Breaking down a compound by heating.
Barium meal
Suspension of BaSO₄ swallowed for X-ray imaging.
HistoryLimelight. Heating calcium oxide produced an intense white glow, used as theatre spotlights in the 1800s before electric lighting.
Fun factMagnesium fire. Burning magnesium is so hot it reacts with water and CO₂, so ordinary extinguishers make it worse; sand is used instead.
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