group 2, 7, periodicity

• Sodium chlorate


  Active ingredient in bleach
• 2F2+20H-OF₂+2F + H₂O


  Chemical reaction
• Fz Oxidise OH ons in of₂

  Chemical reaction
• Brz in simua way to Cl₂

  Chemical reaction
• Benefits of adding O₂ to H₂O

  • Kills bacteria
  • Prevents algal growth
  • Removes bad taste
  • Removes dissolved organic compounds
• Disadvantages of adding O₂ to H₂O

  • Chlorine is toxic
  • Chlorine is a respiratory poison (severe burns)
  • Chlorine can react with organic compounds to form chlorinated hydrocarbons (cancer causing)
• Benefit outweighs risk
• A more reactive (oxidising) halogen


  Will displace a less reactive halide from its group
• Cl₂ with Br


  • Yellow solution forms (Br₂)
• Cl₂ with I


  • Brown solution forms (I₂)
• Br₂ with I


  • Brown solution forms (I₂)
• H2SO4 cannot oxidise F-/CI-
• Conc. H2SO4 reacts with NH3 to form NH4+ and Cl-
• eg. H2S0q+kCI KHSO4 + HCI

  Chemical reaction
• H2SO4 acts as a proton donor
• HBI will form displacement followed by redox

  Chemical reaction
• Br reduces H2S04 to 50₂ (Br- to Br₁₂)

  Chemical reaction
• H2SO4 reduced to SO₂ $ H₂S

  Chemical reaction
• Iodine forms purple vapour/purple black solid
• I₂ + H2SO4 + 2H+ → I₂ + SO₂ + 2H₂O

  Chemical reaction
• S + I₂ + 4H₂O → H₂SO₄ + 4HI

  Chemical reaction
• H2S + I₂ → S + 2HI

  Chemical reaction
• Atomic radius increases down Group 2 due to increase in number of shells
• 1st and 2nd ionisation energies decrease down Group 2 as atomic radius increases, so more shielding and electrons are lost more readily
• Reactivity increases down Group 2 as more shielding means electrons are lost more readily
• Melting and boiling points decrease down Group 2 due to weaker metallic bonding caused by increased shielding
• Electronegativity decreases down Group 2 due to increased shielding, so less attraction for electrons and tendency to form cations
• BaSO4


  Insoluble, used in medicine as a barium meal (x-ray contrast agent)
• Mg(OH)₂


  Magnesium hydroxide, used in indigestion remedies to neutralise excess stomach acid
• Ti


  Titanium, used in joint replacements and aircraft due to low density, high strength and corrosion resistance
• Extracting Ti


  1. TiO₂ + 2C + Cl₂ → TiCl₄ + CO

  2. TiCl₄ + 2Mg → Ti + 2MgCl₂
• Mg does not react with cold water, but reacts with steam to form MgO and H₂
• Ca


  Reacts vigorously with cold water to form Ca(OH)₂
• Sr


  Reacts rapidly with water to form a colourless solution of Sr(OH)₂
• Ba


  Reacts extremely rapidly with water to form Ba(OH)₂
• Solubility of Group 2 metal hydroxides decreases down the group
• Solubility of Group 2 metal sulphates decreases down the group
• Ion tests


  • SO₃ + 2H₂O → 2H₂SO₄
  • Ca(OH)₂ to treat acidic soil
  • NaOH for some metal ions
  • HCl/HNO₃ to remove impurities
  • BaCl₂ to test for sulphates
  • Effervescence test for carbonates
• Atomic radius increases down Group 7
• Electronegativity decreases down Group 7 due to increased shielding