group 7 (halogens)

• trends in group 7

  electronegativity, melting/boiling points, reactivity
• trends in electronegativity

  decreases down the group

  • atomic radius increases
  • more shielding
  • weaker attraction
• trends in melting & boiling points

  increases down the group

  • van der waals forces - depend on the size of the atom
• fluorine:

  pale yellow gas
• chlorine:

  green gas
• bromine

  brown liquid
• iodine

  grey solid
• trends in reactivity

  decreases down the group

  • smaller atomic radius attract larger ions
• oxidising ability

  decreases down the group
• reducing ability

  increases down the group

  • size of ion increases
  • weaker nuclear attraction - more shielding
• strongest oxidising agent

  chloride
• strongest reducing agent

  iodide
• fluoride + SO4

  NaF(s) + H2SO4 (l)  NaHSO4 (s) + HF(g)
• chloride +SO4

  NaCl(s) + H2SO4 (l)  NaHSO4 (s) + HCl
• bromide + SO4

  2NaBr + 3H2SO4  2NaHSO4 + SO2 + Br2 + 2H2O
• iodide + SO4

  NaI(s) + H2SO4 (l)  NaHSO4 (s) + HI(g)
• identifying halides + silver nitrate

  Chlorides produce a white precipitate 

  Bromides produces a cream precipitate

  Iodides produce a yellow precipitate
• 2nd test of halides + ammonia:

  Silver chloride dissolves in dilute ammonia 

  Silver bromide dissolves in concentrated ammonia

  Silver iodide dissolves in neither
• Explain how these forces arise between molecules of chlorine.

  • Random movement of electrons in one molecule - creates a dipole
  • Induces a dipole in a neighbouring molecule.
  • temporary dipoles attract / temporary attraction between δ+ and δ–