Group 7 elements


Colours and states at room temperature

  • Chlorine:
    • Yellow-green gas
  • Bromine:
    • Red-brown liquid
  • Iodine:
    • Purple solid
  • As you go further down, the elements will be solid and darker in colour.
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Halogen reactions

  • Halogens become less reactive down the group
    • It is harder to gain an electron when the distance from the outer shell to the nucleus is greater
  • They react to form salts called metal halides
  • A more reactive halogen will displace a less reactive halogen from a solution of one of its salts in a redox reaction.
    • For example, chlorine displaces bromine from sodium bromine solution
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Hydrogen chloride and hydrochloric acid

  • Hydrogen chloride gas is simply hydrogen and chlorine bonded together
  • Hydrochloric acid is hydrogen chloride gas in solution with water. The ions are separated, so the H+ ions make the solution acidic.

Hydrogen chloride is acidic in water but not methylbenzene.

  • Both water and hydrogen chloride are polar molecules
  • Methylbenzene is a non-polar molecule
  • Polar molecules can only dissolve in other polar molecules
  • When hydrogen chloride dissolves, it produces acidic H+ ions
  • It will not dissolve in methylbenzene so it is not acidic
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