Group 7 Elements

The halogens are all non-metals with coloured vapours

  • Fluorine is a very reactive, poisonous yellow gas
  • Chlorine is a fairly reactive, poisonous dense green gas
  • Bromine is a dense, poisonous red-brown volatile liquid
  • Iodine is a dark grey crystalline solid or a purple vapour
  • They all exist as molecules which are pairs of atoms

Learn these trends

  • As you go down Group 7 the halogens
    • Become less reactive
    • It’s harder to gain an extra electron, because the outer shell’s further from the nucleus
    • Have higher melting and boiling points
    • Have higher relative atomic mass
  • All the Group 7 elements react in similar ways.
  • This is because they all have seven electrons in their outer shell

Halogens can form molecular compounds

  • Halogen atoms can share electrons via covalent bonding with other non-metals so as to achieve a full outer shell
    • For example, HCI, PCI5, HF and CCI4 contain covalent bonds
    • The compounds that form when halogens react with non-metals all have simple molecular structures

Halogens form ionic bonds with metals

  • The halogens from 1-ions called halides
    • F-, CI-, Br- and I-
  • When they bond with metals
    • Na+Ci or Fe3+Br-3
  • The compounds that form have ionic structures
  • The diagram shows the bonding in sodium chloride, NaCI

More reactive halogens will displace less reactive ones

  • A displacement reaction can occur between a more reactive halogen and the salt of a less reactive one
    • E.g. Chlorine can displace bromine and iodine form an aqueous solution of its salt(a bromine or iodine)
    • Bromine will also displace iodine because of the trend in reactivity
    • Cl2 + 2KI - I2 + 2KCI
    • Pale green - Brown
    • CL2 + 2KBr - Br2 + 2KCI
    • Pale green - Orange