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

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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

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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

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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

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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

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