Do they carry current?

The idea

Ionic compounds cannot conduct electricity as solids, where ions are held in fixed positions, but conduct when dissolved in water as ions become free to move; covalent compounds give no ions and are non-conducting.

A salt crystal and salt water

Dry salt crystals are ionic. When they are dissolved in water, the ions are in the water.

Which do you think can carry an electric current?

• Salt dissolved in water, but not the dry crystals
• Dry salt crystals, but not salt dissolved in water
• Both equally

Test the samples

Choose a sample. The picture shows its particles and whether it conducts. This is a picture, not an experiment to try with mains electricity.

Ions must be free

In a solid, the ions of an ionic compound are held in fixed positions by strong forces, so they cannot carry a current. When the compound is dissolved in water, the ions can move. Covalent compounds do not give ions, so they do not conduct, even if they dissolve, like sugar.

Ionic compounds cannot conduct electricity as solids, where ions are held in fixed positions, but conduct when dissolved in water as ions become free to move. Covalent compounds give no ions and are non-conducting.

Notes

Ionic compounds: no conduction as solids (ions fixed), but they conduct dissolved in water (ions free). Covalent compounds give no ions and do not conduct.

Check yourself

Why does solid sodium chloride not conduct electricity?

Why does sodium chloride dissolved in water conduct electricity?

Sugar dissolves in water, but the solution does not conduct. Why?

Which of these does not conduct electricity?

• Its ions are held in fixed positions — correct. Yes!
• It has no ions. Sodium chloride is made of ions. In the solid they are held in fixed positions.
• Its ions are free to move. In the solid the ions cannot move; they are held in fixed positions by strong forces.
• Its molecules start to move. Ionic compounds do not form molecules. The ions become free to move in water.
• Its ions become free to move — correct. Yes!
• The water becomes a solid. The conduction is caused by ions that are free to move in the water.
• Sugar is ionic but its ions are fixed. Sugar is a covalent compound. It gives no ions in solution.
• Sugar does not dissolve. Some covalent compounds, such as sugar, are soluble in water.
• Sugar is covalent and gives no ions in solution — correct. Yes!
• Camphor — correct. Yes!
• Copper sulfate dissolved in water. Ions of copper sulfate are free to move in water, so it conducts.
• Sodium chloride dissolved in water. Ions of sodium chloride are free to move in water, so it conducts.