AQA Chemistry Unit 2: 12 Group 2, the Alkaline Earth Metals

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12.1 The Physical Properties Mg to Ba

  • Group 2: called alkaline earth metals due to their oxides and hydroxides being alkaline
  • They are S-Block element but are less reactive than Group 1

Electron Arrangement

  • All have 2 electrions in the highest energy level

The Sizes of the Atoms

  • Atoms get bigger down the group
  • Atomic radii increases due to extra filled energy level

Melting Points

  • High melting points due to giant metallic structure.
  • Decreases down the group due to sea of delocalised electrons being further away from the nucleus so metallic bonds strength decreases down the group
  • Magnesium has the lowest melting point due to different lattice arrangement of atoms
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Physical Properties Cont.

Ionisation Energies

  • All reactions in group 2 they lose their 2 highest energy electrons to form positive ions
  • M -> M2+ + 2e- : 1st and 2nd Ionisation energies together
  • Both the 1st and 2nd ionisation energies decrease down the group
  • Takes less energy to remove the electrons as they become further away from the nucleus
  • The nucleus also experiences more shielding by extra electron energy level
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The Chemical Properties Mg to Ba

  • Oxidation is the loss of electrons, all group 2 metals are oxidised
  • The metals have oxidation states that change from 0 to 2+
  • These are redox reactions

Reaction with Water

  • The metals get more reactive down the group
  • M(s) + 2H2O(l) -> M(OH)2(aq) + H2(g)
  • Magnesium reacts slowly with cold water but rapidly with steam to form an alkaline oxide and hydrogen:
  • Mg(s) + H20(g) -> MgO(s) + H2(g)
  • Calcium reacts more vigorously, then strontium and barium
  • Calcium Hydroxide (Slaked Lime) is used to treat acidic soil
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Chemical Properties Cont.

Hydroxide

  • Down the group the hydroxides become more soluble
  • The hydroxides are white solids
  • Magnesium Hydroxide is almost insoluble
  • Calcium hydroxide is sparingly soluble, its used in lime water
  • Strontium Hydroxide is more soluble
  • Barium Hydroxide dissolves to produce a strong alkaline solution
  • Ba(OH)2(s) + aq -> Ba2+(aq) + 2(OH)-(aq)

Sulfates

  • They become less soluble down the group
  • Barium Sulfate:outlines the gut as it absorbs x-rays and since it's insoluble it's safe
  • Barium sulfate is used to test sulfate ions: first acidified with nitric/hydrochloric acid, barium chloride is added to the solution, if sulfate is present a white precipitate is formed
  • Ba2+(aq) + SO4-2(aq) -> BaSO4(s)
  • The acid removes carbonate ions
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