Group 7

• Atomic Radius increases down the group.
• Reactivity decreases down the group.
• First ionisation energy decreases down the group.
• First Ionisation Energy - the energy required to remove one mole of electrons from one mole of atoms in the gaseous state.
• Electronegativity decreases down the group.
• Electronegativity - the power of an atom to attract a shared pair of electrons in a covalent bond
• Melting point increases down the group.
• Appearance of diatomic atom -

  • F - Yellow gas
  • Cl - Green gas
  • Br - Red/brown liquid, with red/brown vapour
  • I - Grey/black solid, sublimes to violet vapour
• Dissolved in aqueous solution -

  • F - NVC
  • Cl - Pale Green
  • Br - Orange
  • I - Brown
• Dissolved in organic solvent -

  • F - NVC
  • Cl - Pale green
  • Br - Orange
  • I - Purple
• The halogens are sparingly soluble in water as they are non-polar. Solubility decreases as you go down the group.
• Oxidising agent - a species that accepts electrons
• The oxidising power of the halogens decreases down the group. This is because the halogen has a larger atomic radius and more shielding.
• Reducing agent - a specie that donates electrons.
• The reducing power of halide ions increases down the group. This is because the halide ion has a larger ionic radius and more shielding, so there is a weaker attraction between the nucleus and the outer electrons.
• Chlorine is a good oxidising agent so will oxidise bromide and iodide ions. Bromine will not oxidise chloride ions, but it will oxidise iodide ions. Iodine is a poor oxidising agent so will not oxidise chloride or bromide ions.
• Iodide ions, are good reducing agents, so will reduce chlorine and bromine. Bromide ions will not reduce iodine, but will reduce chlorine. Chloride ions are poor reducing agents and will not reduce bromine or iodine.
• NaF + H2SO4 --> NaHSO4 + HF

  Observations: white misty fumes
• NaCl + H2SO4 --> NaHSO4 + HCl

  Observations: white misty fumes
• NaBr + H2SO4 --> NaHSO4 + HBr

  Observations: white misty fumes
• 2NaBr + 3H2SO4 --> 2NaHSO4 + Br2 + SO2 + 2H2O

  Observations: brown vapour + choking gas