Group 2, Alkaline Earth metals

• Properties & trends of Group 2: 1st ionisation energy

  trend: decreases

  • higher nuclear charge
  • shielding increases
  • atomic radius increases

  
• Properties & trends of Group 2: melting point

  trend: decreases

  • 2e- delocalised for all atoms in metallic bonding
  • same no. of electrons more spread out
  • ion gets bigger going down group
  • Mg is an exception due to structure

  
• Properties & trends of Group 2: reactivity+ solubility

  trend: increases going down

  • Be is a metalloid so we forget it
  • magnesium + liquid water -> magnesium hydroxide + H2
  • liquid water -> very slow reaction
  • steam -> very fast reaction

  Mg(s) + H2O(g) -> MgO(s) + H2(g)

  Ca(s) + H2O(g) -> Ca(OH)2(s) + H2(g)

  • same with all group 2 metals
  • solubility increases going down the group
• Reactions & Uses of Group 2

  metal + water -> metal hydroxide + hydrogen

  • Group 2 hydroxides get more soluble down the group
  • Mg(OH)2 -> pH 9 & Ba(OH)2 -> pH 13-14

  XSO4 -> X2+(aq) + SO4^2-(aq)

  • group 2 sulfates get less soluble going down group
  • MgSO4 -> high solubility & BaSO4 -> insoluble in water
  • test for sulfate ions: add HCl & BaCl2
  • if present -> BaSO4 formed -> white precipitate formed
  • can use HNO3 instead of HCl
• Reactions & Uses of Group 2

  Use of Mg -> extraction of titanium

  • extraction with carbon forms titanium carbide which is difficult to purify

  1. react ore with HCl -> obtain TiCl4
  2. TiCl4 + 2Mg -> 2MgCl2 + Ti

  • ionic: Ti4+ + 2Mg -> 2Mg2+ + Ti
  • half equations: Ti4+ + 4e- -> Ti & 2Mg -> 2Mg2+ + 4e-

  Use of calcium hydroxide Ca(OH)2 -> 'lime'

  • used in farming to adjust soil pH & forms limewater, forming CaCO3 when reacted with CO2
• Reactions & Uses of Group 2

  Use of barium sulfate -> 'barium meal'

  • used in X-rays to show soft tissue (mainly gut)
  • doesn't get absorbed into body

  Use of CaO -> used in industry to react with SO2

  • CaO + SO2 -> CaSO3 (neutralisation reaction)
• ID tests

  • Test for Barium (Ba2+) ions
  • add H2SO4
  • if present -> white precipitate formed

  Ba2+(aq) + SO4^2-(aq) -> BaSO4(s)

  • Test for Magnesium (Mg2+) ions
  • add NaOH
  • if present -> white precipitate formed

  Mg2+(aq) + OH-(aq) -> Mg(OH)2(s)
• ID tests

  • Test for ammonium (NH4^+) ions
  • add NaOH & test with damp red litmus paper at mouth of tube
  • if present -> litmus paper turns blue

  OH- + NH4^+ -> NH3 + H2O

  • Test for sulfate (SO4^2-) ions
  • Add BaCl2 & dilute HCl (HCl removes impurities)
  • if present -> white precipitate formed

  Ba2+(aq) + SO4^2-(aq) -> BaSO4(s)

  • Test for carbonate (CO3^2-) ions
  • add HCl & bubble through lime water (forms CaCl2)
  • if present -> effervescence & limewater goes cloudy

  2H+(aq) + CO3^2-(aq) -> H2O(l) + CO2(g)