Giant ionic structures
3 marks · NormalExplain why giant ionic structures conduct electricity when molten but do not conduct when solid.
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Must show: Ions fixed in solids, Ions free to move in molten state, Movement of ions allows current
Also accept: References to dissociation in solution (if not about solubility)
Common mistakes: Saying electrons move; Saying solid conducts
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Marking points
M1 · 1 mark · States that in solid ionic compounds, ions are fixed in the lattice and cannot move.
M2 · 1 mark · In molten ionic compounds, the lattice breaks down and ions are free to move.
A1 · 1 mark · Explains that electrical current is carried by the movement of ions.
Worked solution
In solid giant ionic structures, the ions are fixed in position in the lattice and cannot move, so the solid cannot conduct electricity.
When molten, the lattice breaks apart, so ions are free to move around.
The movement of these ions allows an electric current to flow through the liquid.