Group 2, Group 17, Redox

• Redox Reaction Group 2 Metal with Oxygen

  metal + oxygen -> metal oxide
• Redox Reaction Group 2 Metal and Water

  metal + water -> metal hydroxide + hydrogen
• Redox Reaction Group 2 Metal and Acid


  Metal + Acid -> Salt + Hydrogen
• Reactivity Increase Down Group 2


  Down gp 2:

  • Nuclear charge increases
  • More shielding
  • Increases atomic radius

  Weaker electrostatic attraction from nucleus to outer e- ∴ outer 2 e- more easily lost
• Group 2 Oxide and Water

  metal oxide + water -> metal hydroxide
• pH of Group 2 Hydroxides Increases Down Group 2 


  Down gp2:

  • Ionic radius greater
  • More shielding
  • Weaker electrostatic attraction so OH⁻ less attracted to gp2 ion
• Commercial use of Ca(OH)₂


  Use: Neutralise excess acid in soil

  Explanation: Plants cannot have conditions to acidic

  Disadvantage: if too much is used, soil will be too alkaline & damages crops
• Commercial use of Mg(OH)₂


  Use: Neutralises excess stomach acid

  Explanation: Safe for human consumption
• Thermal Decomposition of Metal Carbonates


  metal carbonate -> metal oxide + carbon dioxide
• Thermal Decomposition of Group 2 Carbonates Decreases down group


  Down gp 2:

  • Ionic Radius greater
  • More shielding
  • Weaker nuclear attraction ∴ less able to attract an O off CO₃²⁻
• Writing and balancing redox equations

  
• Group 7 Boiling Point


  Down gp 17:

  • b.p. increases
  • More electrons so larger temporary dipoles
  • Stronger London Dispersion forces between molecules, needing more energy to overcome
• Why the Oxidising power of Halogens Decreases down the group


  down gp 17:

  • More shielding
  • Atomic radius increases
  • Weaker nuclear attraction from nucleus so harder to gain e- ∴ weaker oxidising agent
• Group 7 element Physical appearance at RTP


  • Fluorine- yellow gas
  • Chlorine- green gas
  • Bromine- brown liquid
  • Iodine- purple solid
• Halogen Solution Colour in Aqueous Solution


  Does not have same intermolecular force -> does not dissolve well

  Chlorine- green

  Bromine- orange

  Iodine- brown
• Halogen Solution Colour in Organic solvent


  London dispersion forces

  Chlorine- green

  Bromine- orange

  Iodine- purple
• • Halide ions are colourless
  • Diatomic molecules give rise to colour in aqueous solution or organic solvent
• Reaction of Chlorine with Water


  Cl₂ + H₂O -> HClO + HCl
• Using chlorine in water purification


  ✓ Kills bacteria

  ✗ Toxic gas

  ✗Reacts with organic matter to form chlorinated hydrocarbons (which are carcinogenic)
• Chlorine in the formation of Bleach/ Sodium chlorate (I)


  Cl₂ + 2NaOH -> NaClO + H₂O + NaCl

  (Cold, dilute sodium hydroxide)