Halogens

• Halogens


  The elements in group 7 of the periodic table
• Halogens


  • fluorine
  • chlorine
  • bromine
  • iodine
  • astatine
• Why are they called the 'halogens'?

  They are very reactive non metals, never found free in nature because of their reactivity, and are found as compounds with metals (salts)
• Halogens


  • They are all toxic or harmful because they are so reactive
  • Before antiseptics, iodine was used to clean wounds as it is harmful to all things, including bacteria
• Electron structure of halogens

  All halogens have seven electrons in their outer shell, and can easily obtain a full outer shell by gaining one electron
• Halogens all gain an electron in reactions to form negative ions with a -1 charge
• How do halogen molecules exist?

  Each atom can achieve a full outer shell by sharing one electron with another atom to form a single covalent bond, so all halogens exist as diatomic molecules
• General properties of the halogens

  • Poisonous and smelly
  • Brittle and crumbly when solid
  • They become darker in colour down the group
• Halogens are non-metals and so do not conduct electricity
• Physical state of the halogens

  The melting and boiling points of the halogens increase down the group, as the molecules become bigger. Astatine is a solid at room temperature.
• Halogen vapours


  Bromine and iodine have low boiling points, so they produce vapour at relatively low temperature. Iodine can change directly from a solid to a gas without becoming a liquid, which is called sublimation.
• How do the halogens react with metals?

  Halogens readily react with most metals to form ionic compounds called metal halides, as halogens need to gain electrons and metals need to lose electrons.
• Halides


  When halogens react, they become negative ions by gaining an extra electron, and the name of the halogen changes to end in '-ide' instead of '-ine'.
• The reactivity of the halogens decreases as you go down the group.
• Equations of halogens and iron

  Halogen + iron → iron (III) halide
• Electron structure affects reactivity

  The reactivity of the halogens decreases going down group 7 because the atoms get larger, the outer shell is further from the nucleus and shielded by more electron shells, making it harder to attract another electron.
• Displacement of halogens


  A more reactive halogen will always displace a less reactive halide from its compounds in solution.
• Uses of fluorine and its compounds

  • Fluoridation of water, to prevent tooth decay
  • Toothpaste, to prevent tooth decay
  • Polymers, e.g. Teflon for non-stick pans
  • Processing uranium nuclear fuel
• Uses of chlorine and its compounds

  • Chlorination of water, to kill microorganisms
  • To make bleach
  • Used in the production of paper, paints, plastic products
• Uses of bromine and iodine and their compounds

  • Medicines
  • Antiseptics and water purification tablets
  • Leaded petrol
  • Agriculture
  • Photography
  • Animal feed supplements