Giant ionic structures
3 marks · EasyThe table shows properties of two substances.
| Substance | Melting point (°C) | Electrical conductivity (solid) | Electrical conductivity (liquid) |
|---|---|---|---|
| Sodium fluoride (NaF) | 998 | No | Yes |
| Phosphorus trichloride (PCl_3 | -112 | No | No |
Which substance has a giant ionic structure?
State one piece of evidence from the table that supports your answer in (a).
Explain why sodium fluoride conducts electricity when molten but not when solid.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Sodium fluoride (NaF)
(b) It has a high melting point / conducts electricity when molten.
(c) When molten, ions are free to move and carry charge; in solid, ions are in fixed positions. · must show Movement of ions in molten state, No movement in solid
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Marking points
B1 (a) · 1 mark · Correctly chooses sodium fluoride as the giant ionic structure
B1 (b) · 1 mark · Gives correct evidence (high melting point or conducts when molten)
B1 (c) · 1 mark · Explains that molten ions move, while solid ions do not
Worked solution
a) Sodium fluoride (NaF)
b) It has a high melting point.
c) In the molten state, the ions in NaF are free to move and carry charge; in the solid, the ions are locked in fixed positions and cannot move, so no conduction occurs.