9 Group 2

• Atomic radius going down Group 2

  Atomic radius increases down the group.

  As one goes down the group, the atoms have more shells of electrons making the atom bigger
• Melting points going down Group 2

  Melting points decrease down the group

  The metallic bonding weakens as the atomic size increases

  The distance between the positive ions and delocalized electrons increases

  electrostatic attractive forces between the + ions and the delocalized electrons weaken
• Reactivity of Group 2 metals

  Increases down the group
• Magnesium will react slowly in oxygen without a flame
• Reaction of magnesium with oxygen

  2 Mg + O2 → 2 MgO
• Reaction of magnesium with hydrochloric acid

  Mg + 2 HCl → MgCl2 + H2
• Reaction of magnesium oxide with hydrochloric acid

  MgO + 2 HCl → MgCl2 + H2O
• The group 2 metals will burn in oxygen
• Magnesium oxide (MgO)

  A white solid with a high melting point due to its ionic bonding
• Reaction of magnesium with steam

  Mg(s) + H2O(g) → MgO(s) + H2(g)
• The other group 2 metals will react with cold water with increasing vigour down the group to form hydroxides
• Reaction of calcium with water

  Ca + 2 H2O (l) → Ca(OH)2 (aq) + H2 (g)
• Reaction of strontium with water

  Sr + 2 H2O (l) → Sr(OH)2 (aq) + H2 (g)
• Reaction of barium with water

  Ba + 2 H2O (l) → Ba(OH)2 (aq) + H2 (g)
• Reaction of magnesium with warm water

  Mg + 2 H2O → Mg(OH)2 + H2
• The reaction of magnesium with warm water is much slower than the reaction with steam and there is no flame
• Titanium cannot be extracted with carbon because titanium carbide (TiC) it is formed rather than titanium
• Titanium is extracted by reaction with a more reactive metal (e.g. Magnesium)
• Steps in extracting titanium

  1. TiO2 (solid) is converted to TiCl4 (liquid) at 900°C

  2. The TiCl4 is purified by fractional distillation in an argon atmosphere

  3. The Ti is extracted by Mg in an argon atmosphere at 500°C
• Calcium oxide can be used to remove SO2 from the waste gases from furnaces (e.g. coal fired power stations) by flue gas desulfurisation
• Reaction of calcium oxide with sulfur dioxide

  SO2 + CaO → CaSO3
• The calcium sulfite which is formed can be used to make calcium sulfate for plasterboard
• Group II sulfates become less soluble down the group, with BaSO4 being the least soluble
• Barium chloride solution acidified with hydrochloric acid


  A reagent used to test for sulfate ions
• Reaction of barium chloride with a solution containing sulfate ions

  Ba2+ (aq) + SO4

  1. (aq) → BaSO4 (s)
• Barium sulfate is used in medicine as a 'Barium meal' given to patients who need x-rays of their intestines
• Barium sulfate is safe to use because its low solubility means it is not absorbed into the blood
• Reaction of barium metal with sulfuric acid

  Ba + H2SO4 → BaSO4 + H2
• The same effect happens to a lesser extent with metals going up the group as the solubility of the sulfates increases
• Hydrochloric acid is needed to react with carbonate impurities that are often found in salts which would form a white barium carbonate precipitate and so give a false result
• Formation of a precipitate when barium chloride is added to a solution containing sulfate ions

  SrCl2(aq) + Na2SO4 (aq) → 2NaCl (aq) + SrSO4 (s)
• Simplified ionic equation for the formation of the precipitate

  Sr2+ (aq) + SO4

  1. (aq) → SrSO4 (s)
• Group II hydroxides become more soluble down the group
• All Group II hydroxides when not soluble appear as white precipitates
• Calcium hydroxide


  Partially soluble in water, appears as a white precipitate, used in agriculture to neutralise acidic soils
• Lime water

  An aqueous solution of calcium hydroxide, can be used as a test for carbon dioxide
• Reaction of lime water with carbon dioxide

  Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O(l)
• Barium hydroxide


  Easily dissolves in water, making the solution strongly alkaline
• Magnesium hydroxide

  Insoluble in water, appears as a white precipitate, slightly alkaline (pH 9)
• medical use for magnesium hydroxide

  used in medicine in milk of magnesia to neutralise excess stomach acid and to treat constipation