Group 2 - Alkaline earth metals

Trend in melting point

• Decreases down the group

• Because it has a metallic structure

• The larger the ions, the weaker the attractive forces between positive ions and delocalised electrons

Trend in atomic radius

• Increases down the group

• Because of additional electron shells

Trend in ionisation energy

• Decreases down the group

• Because atomic radius increases

• Because shielding increases

Trend in reactivity

• Increases down the group

• Increased electron shielding down the group

• Outer electron easier to lose

Reactions of Mg-Ba with cold water (not steam)

Mg + 2H2O → Mg(OH)2 + H2

• Forms metal hydroxide and hydrogen

• Redox reaction, magnesium is oxidised

Magnesium and steam

Mg + H2O → MgO + H2

• Mg burns with bright white flame

• Forms white powder, magnesium oxide

Use of magnesium in extraction

• Used to extract titanium from TiCl4 via displacement

• TiCl4 + 2Mg → 2MgCl2 + Ti

Flue gas removal

• Calcium oxide or carbonate reacts with SO2 to remove it from factory pollutants

• Prevents it from being released into the atmosphere

• CaO + 2H2O + SO2 → CaSO3 + 2H2O

Relative solubilities of hydroxides of Mg-Ba in water

• Mg(OH)2 = Insoluble

• Ca(OH)2 = Slightly soluble

• Sr(OH)2 = Soluble

• Ba(OH)2 = Soluble

Relative solubilities of Mg-Ba sulphates in water

• MgSO4 = Soluble

• CaSO4 = Slightly insoluble

• SrSO4 = Insoluble

• BaSO4 = Insoluble

Use of Mg(OH)2 and of Ca(OH)2

• MgOH)2 - used as an antacid in medicine, neutralises acids

• Ca(OH2) - used in a similar way in agriculture for soil, neutralises acids

Use of BaCl2

• Used in test for sulphate ions

• Because it forms BaSO4 which is a white precipitate

• Must be acidified with HCl as chloride ions will react with any carbonate ions and remove them to stop a false positive occuring

Use of BaSO4

• Used in barium meals, medical tracer

• Because it is insoluble and cannot be absorbed