Group 7 - Halogens

• 7 - diatomic molecules
• Fluorine - F2 - poisonous, yellow gas
• Chlorine - Cl2 - poisonous, dense, green gas
• Bromine - Br - dense, poisonous, red - brown, volatile liquid/ orange vapour
• Iodine - I - poisonous, dark grey crystalline solid / purple vapour
• Astatine - At - black
• Reactivity decreases down the group
• Melting / boiling points increase down the group
• Less reactive further down the group due to:

  • increased distance between outer electron shell and nucleus which means
  • less attraction from the nucleus to pull electrons into the atom so
  • outer electron shell unlikely to gain an electron
• When halogens gain electrons they form


  1 - ions, called halide ions