halogens

• flourine 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
• as you go down group 7 the halogens :

  • become less reactive - its harder to gain an extra electron because the outer shells further from the nucleus
  • have higher melting and boiling points
  • have higher realtive atomic masses
• all group seven elements react in similar ways this is because they all have seven electrons in their outer shell
• a displacement reaction can form 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)