group 7

• Atomic radius

  • increases down the group due to additional electrons shells
• Reactivity

  • decreases down the group -> atomic radius and shielding increases so the positive attraction of the nucleus is weakened making it more difficult to attract an electron
• Ionisation energy

  • 1st ionisation energy decreases down the group -> greater atomic radius and increased amounts of shielding
• Boiling point

  • increases down the group --> grp 7 are simple covalent molecules so held together by van der waals forces
  • strength of these intermolecular forces increases as mass increases -> strength of VDWF increase dwon the group so more energy needed to overcome them
• Oxidising power

  • halogens are good oxidising agents
  • oxidising power decreases down the group as their ability to attract electrons decreases due to shielding and atomic radius
  • this means a halogen will displace any halide beneath it
• Halide ions

  • good reducing agents as they donate electrons to the species being reduced and are oxidised
  • reducing power increases down the group as electrons are easier to lose from larger ions due to shielding and a larger atomic radius
• Electronegativity

  • decreases dwon the group --> F2 the highest as it has smallest atomic radius & minimal shielding
  • weak fluorine bonds -> non-bonded electrons create repulsion
• Bleach

  • 2NaOH + Cl2 --> NaClO + NaCl + H2O
  • cold & dilute NaOH
  • disproportionation reaction (Cl oxidised and reduced)
• Clorine and water

  • Cl2 + H2O --> 2H+ + Cl + ClO-
  • disproportionation reaction
  • in UV: Cl2 + H2O --> 2Cl- + 1/2O2
  • in Uv: 2Cl2 + 2H2O --> 4HCl + O2
• • F & Cl are bad reducing agents -> general acid base reaction
  • Br & I are good reducing agents -> redox reaction (Na+ spectator ion)
• F & Cl ions

  • NaF + H2SO4 --> NaHSO4 + HF
  • NaCl + H2SO4 --> NaHSO4 + HCl
• Bromide ions

  • NaBr + H2SO4 --> NaHSO4 + HBr
  • 2HBr + H2SO4 --> Br2 + SO2 + 2H2O
  • observation: brown/orange fumes, choking fumes
• Iodide ions

  • NaI + H2SO4 --> NaHSO4 + Hi
  • 2HI + H2SO4 --> I2 + SO2 + 2H2O
  • 6HI + H2SO4 --> 3I2 + S + 4H2O
  • 8HI + H2SO4 --> 4I2 + H2S + 4H2O
• Testing for halide ions

  
• Test for SO42- ions

  • tested using BaCl2 -> forms a white precipitate
• Test for OH- ions

  • these ions indicate that a substance is alkaline
  • can be identified with red litmus paper which turns blue
  • or using universal indicator blue -> purple
• Test for CO32- ions

  • when acid (HCl) is added substance containing carbonate ions will fizz (effervescense) & CO2 gas is given off
  • gas can be collected and bubbled through limewater which will turn cloudy (confirming it as CO2)
• Test for NH4 + ions

  • if ammonium ions are present NH3 gas will be given off
  • tested by holding damp red litmus paper over a petri dish of the substance being tested -> will turn blue
  • can be tested same way but by adding NaOH to produce the gas faster