Group 7 Elements

• The group 7 elements are known as the halogens
• 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
• Fluorine, chlorine, bromine and iodine are all molecules which are pairs of atoms
• As you go down group 7, the halogens:

  -Become less reactive. It's harder to gain an extra electron, because the outter shell's further from the nucleus

  -Have higher melting and boiling points

  -Have higher relative atomic masses
• You can use trends to predict the properties of halogens. E.g. iodine will have a higher boiling point than chlorine as it's further down in the group
• All group 7 elements react in similar ways. This is because they all have 7 electrons in their outter 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. E.g. HCl contains a covalent bond
• The compounds that form when halogens react with non-metals all have simple molecular structures
• Halogens form ionic bonds with metals
• The halogens form 1- ions called halides (F-, Cl-, Br-, I-) when they bond with metals e.g. Na+ Cl-
• 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 from an aqueous solution of its salt (a bromide or iodide)
• Bromine will also displace iodine because of the trend in reactivity
• Displacement reaction:

  (pale green) (brown)

  Cl2(g) + 2Kl(aq) -> I2(aq) + 2KCl(aq)