Group 2, the alkaline earth metals

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  • Created by: ED
  • Created on: 22-03-15 21:19
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  • Group 2
    • Physical properties
      • Oxides and hydroxides are alkaline.
      • S-block elements
      • Down the group
        • Larger atomic radius
        • More electron shells
        • Outer electrons are further away from positive nucleus
        • Strength of metallic bond decreases hence lower melting & boiling points.
          • Magnesium does not fit the trend because its lattice arrangement is different hence is easier to separate
        • First and second ionisation energies decrease due to more effective electron shielding
      • Metals
    • Chemical properties
      • Reacting with (cold) water forms hydroxides and hydrogen and is slow
        • Down the group reactions with water are more reactive
        • X(s)+2H2O(l) ->X(OH)2(aq) + H2(g)
      • Magnesium hydroxide is "milk of magnesia"
        • Used in indigestion remedies to neutralise excess stomach acid
      • Reacting with steam is rapid and forms an alkaline oxide and hydrogen
        • X(s)+H2O-> XO(s)+H2(g)
      • Calcium hydroxide, slaked lime, is used to treat acidic soil.
      • They all create white precipitates but down the group the hydroxides become more soluble
        • Magnesium hydroxide is (almost) insoluble
        • Calcium hydroxide is sparingly soluble
        • Strontium hydroxide is (more/ extremely) soluble
        • Barium hydroxide is soluble and dissolves to make a strongly alkaline solution
      • Sulfates
        • Unlike hydroxides, sulfates are less soluble down the group
        • Barium Sulfate, BaSO4, is (virtually) insoluble hence used in medicine to outline the gut in medical X-rays
          • It is taken by the mouth as "Barium meal" and the heavy barium atom is good at absorbing X-rays.
          • Barium compounds are highly toxic but barium sulfate is insoluble hence safe.
    • X->(X^2+)+e-

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