Group 2 and 7

• Down group 2 - atomic radius increases because there are more occupied energy levels.
• Down group 2 - 1st ionisation energy decreases because atomic radius increases so the distance between the nucleus and the outer electron increases and there is more shielding of nuclear charge so attraction is less.
• Down group 2 - electronegativity decreases because there is increased shielding so electrons are further from the nucleus so there is decreased attraction for the bonding pair of electrons.
• Down group 2 - melting point decreases as the size of the metal ion increases so attraction between the nucleus and the delocalised electrons decreases.
• Be + Water -> no reaction, no observation
• Mg + Water -> Mg(OH)2 + Hydrogen

  white solid formed, reacts slowly
• Mg + Steam -> MgO + Hydrogen

  white solid formed, reacts vigorously
• Ca + Water -> Ca(OH)2 + Hydrogen

  turns cloudy as calcium hydroxide isnt very soluble, reacts steadily
• Sr + Water -> Sr(OH)2 + Hydrogen

  wont turn cloudy, reacts quickly
• Ba + Water -> Ba(OH)2 + Hydrogen

  reacts immediately
• Down group 2 - solubility of hydroxides increases
• Down group 2 - solubility of sulfates decreases
• To test for sulphates:

  • Acidify to remove carbonate ions
  • Add BaCl2 or Ba(NO3)2
  • White precipitate BaSO4 will form if sulphate is present
• Down group 7 - melting point increases because the molecules get bigger so have more electrons so there are more VdW.
• Down group 7 - electronegativity decreases because atoms are bigger so more shielding so decreased attraction between the nucleus and the bonding pair of electrons in a covalent bond.
• Chlorine + Bromide ions: orange solution formed
• Chlorine + Iodide ions: brown solution formed
• Bromine + Chloride ions: No reaction, stays orange
• Bromine + Iodide ions: brown solution formed
• Iodine + Chloride ions: no reaction, stays brown
• Iodine + Brommide ions: no reaction, stays brown
• Group 7 in pure form:

  • Flourine - pale yellow gas
  • Chlorine - pale green gas
  • Bromine - dark red liquid
  • Iodine - grey solid
• Test for halides:

  • Add AgNO3
  • ^Use HNO3 to acidify
• Results for halides test:

  • Flourine - no visible change
  • Chlorine - white precipitate
  • Bromine - cream precipitate
  • Iodine - yellow precipitate
• Solubilities of precipitates formed from halide test:

  • AgCl - soluble in d. NH3 - soluble in c. NH3
  • AgBr - insoluble in d. NH3 - soluble in c. NH3
  • AgI - insoluble in d. NH3 - insoluble in c. NH3
• Group 2 - test for carbonates:

  • Add HCl
  • Effervescence
• Group 2 - test for ammonium:

  • Add concentrated NaOH
  • Effervescence
  • Fumes trun litmus paper blue
• Reducing power of the halides increases down the group.
• Chloride + H2SO4:

  • NaCl + H2SO4 -> NaHSO4 + HCl
  • White steamy fumes of HCl
  • Acid-base reaction
• Bromide + H2SO4:

  • NaBr + H2SO4 -> NaHSO4 + HBr
  • White steamy fumes of HBr
  • Acid-base reaction^
  • 2Br- + 2H+ + H2SO4 -> SO2 + Br2 + H2O
  • Orange solution of Br2
  • Choking gas of SO2
  • Reduction (+6 to +4) ^
• Iodide + H2SO4:

  • NaI + H2SO4 -> NaHSO4 + HI
  • White steamy fumes of HI
  • Acid - base reaction ^
  • 2I- + H2SO4 + 2H+ -> I2 + SO2 + 2H2O
  • Purple vapour of I2
  • Choking gas of SO2
  • Reduction (+6 to +4) ^
  • 6I- + H2SO4 + 6H+ -> 3I2 + S + 4H2O
  • Yellow solid of S
  • Reduction (+6 to 0) ^
  • 8I- + H2SO4 + 8H+ -> 4I2 + SH2 + 4H2O
  • Smell of rotten eggs - SH2
  • Reduction (+6 to -2) ^