Group 7 elements

• 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.

• 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

• 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