Group 7

Topic 1 - Atomic Structure & Periodic Table
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Melting & Boiling Point

 

Look at Figure 1. Explain the trend in boiling points down Group 7.

Table showing boiling points, melting points and state at room temperature of group 7 elements (halogens) going down the group (Chlorine, Bromine, Iodine).

[4 marks]

  • Group 7 elements form small molecules. (1 marks)

    Individual chlorine atoms are held in together in pairs with:

    • Strong covalent bonds

    Different chlorine molecules are held together with:

    • Weak intermolecular forces

Both strong covalent bonds shown holding Chlorine atoms in pairs and weak intermolecular forces between the chlorine molecules.

  • We do NOT need to break the covalent bonds!

    To melt/ boil chlorine we only break the weak intermolecular forces.

    This requires a small amount of energy.

Chlorine's weak intermolecular forces broken to melt or boil it.

  • More electrons as you go down. And more electron shells.

    So larger molecules. (1 mark)

    So stronger intermolecular forces. (1 mark)

    More energy is needed to break them. (1 mark)

    So higher melting and boiling points.

Increasing number of electron shells and molecule sizes of Halogens going down the group (Chlorine, Bromine, Iodine) so stronger intermolecular forces.
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