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Giant ionic structures.

Properties of giant ionic structures explained.

Question 1.
Why do ionic compounds have high melting points?

  • They have a rigid giant lattice structure
  • There are many strong electrostatic attractions between cations and anions
  • It therefore takes a lot of energy to break the structure apart

Question 2.
Why do ionic compounds conduct electricity when molten but not when solid?

  • Ions can carry an electric charge when they are free to move around
  • In a solid the ions are bonded together strongly and are unable to move around
  • When melted, the ionic bonds are broken, the lattice breaks apart, and the ions move around freely.

Note that aqueous ionic solutions can conduct electricity for the same reason – the ions move freely in the solution. See an animation here.

All ions are charged. So positively charged ions move towards the negative electrode and anions move towards the positively charged electrode. As ions are moving, the charge is moving. This movement of charge produces current

See my simple animated gif here.

Question 3.
Why are ionic compounds brittle?

When an ionic crystal is tapped with a hammer the following happens.

  • Layers of ions are displaced
  • Ions of like charge come together
  • Attractions are replaced by repulsions
  • The ions push apart and the crystal shatters.
 
When metals are hammered, the layers of cations slide over one another too. However, the delocalised electrons in a metal prevent repulsions between the cations. That makes metals malleable.

See my simple animated gif here.

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