Group 7

• What is the colour and state of bromine at room temperature?

  Red liquid.
• What is the colour and state of chlorine at room temperature?

  Green, gas.
• What is the colour and state of iodine at room temperature?

  Dark grey solid that gives off purple vapour when heated.
• As you go down Group 7, the melting points and boiling points increase.
• You can use the trends in physical properties from chlorine to iodine to predict the properties of halogens further down the group. For example, you can see that melting point increases down the group, and the colours of the halogens get darker, so you could predict that astatine (which comes below iodine) would be a dark-coloured solid at room temperature.
• What is the chemical test for chlorine?

  Damp blue litmus paper - the chlorine gas would bleach it and turn it white.
• As you go down the group, the reactivity decreases because the electron shells are far from the nucleus. This makes it hard to gain an electron because of the weak electrostatic force of attraction.
• When a halogen reacts with water, it forms an acidic solution.
• Hydrochloric acid is produced by the reaction between hydrogen and chlorine
• Halogens react with metals to form salts.
• Chlorine reacts with hydrogen to form hydrochloric acid.
• 1. Group 7 elements undergo displacement reactions.
  2. Displacement: A more reactive element displaces less reactive.
  3. Halogen displacement is redox: Halogens gain, halide ions lose electrons.
  4. Chlorine displaces bromine due to higher reactivity.
  5. Chlorine reduces to chloride ions, forming potassium chloride; bromide oxidizes to bromine, turning the solution orange.

  
• • Halogen displacement: More reactive halogen displaces less reactive one from salt solution.
  • Colour change indicates displacement reaction occurred.
  • Example: Chlorine displaces bromine, iodine; bromine displaces iodine.
  • Reactivity trend: Halogens become less reactive down the group.
  • Astatine, the least reactive, is unlikely to displace other halogens.

  
• In terms of electron configurations, a halogen would gain 1 electron giving it a -1 charge. It exists diatomically and shares a pair of electrons with the halogen next to it.