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