A-Level Chemistry AQA Notes

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Group 2, Alkaline Earth Metals

All Group 2 elements have 2 electrons in their outer s-subshell.
Down the group ionisation energy decreases, as the atomic radius and shielding increases, decreasing the attraction of the electron to the nucleus
Melting point also decrease down the group due to the increased atomic radii and shielding, so metallic bonding is weaker
Group 2 elements react with water to form hydroxides and hydrogen gas

Mg (s) + 2H2O(l) → Mg(OH)2 (aq) + H2 (g)
Oxidation numbers: 0 +1 +2 0

Mg (s) + H2O (g) → MgO (s) + H2 (g)
Oxidation numbers: 0 +1 +2 0

Group 2 Element	Group 2 Hyroxide	Solubility of Hydroxide
Mg	Mg(OH)2	Slightly soluble
Ca	Ca(OH)2	Sparingly soluble
Sr	Sr(OH)2	More soluble than Mg(OH)2 and Ca(OH)2
Ba	Ba(OH)2	Most soluble

Mg(OH)2 (milk of magnesia) is used to neutralise excess hydrochloric acid in the stomach, relieving indigestion
Titanium oxide reacts with carbon and chlorine to form titanium chloride, which is purified by fractional distillation and then reduced to titanium using magnesium
- TiCl4(l)+ 2Mg(s)→ 2MgCl2 (s) + Ti (s)
Ca(OH)2 (hydrated lime) is used to neutralise acidic soil
CaO and CaCO3 can be used to remove SO3 from flue gases

CaO (s) + 2H2O (l) + SO2 (g) → CaSO3 (s) + 2H2O (l)
CaCO3 (s) + 2H2O (l) + SO2 (g) → CaSO3 (s) + 2H2O (l) + CO2 (g)

BaSO4 can be ingested to visual soft tissue in imaging
Acidified BaCl2 can be used to test for the presence of sulphate ions as barium sulphate, a white precipitate, will be formed. The solution needs to be acidified to remove any sulphites or carbonates, which would result in the formation of a white precipitate

Ba^2+ (aq) + SO4^2+(aq) → BaSO4(s)