How can ionic substances conduct electricity

The ions are surrounded by water molecules. Although a water molecule is neutral overall, it has a weak positive charge near its hydrogen atoms, and a weak negative charge near its oxygen atom. Water molecules surround the ions in solution because they are attracted by the charges of the ions.

Properties of ionic compounds The physical properties of ionic compounds can be explained by their giant ionic lattice structure and ionic bonds. Melting points Ionic compounds are held together by many strong electrostatic forces between the oppositely charged ions. When an ionic substance is molten or dissolved, the ions that make it up are free to move within the substance and carry charge through it, i. However when an ionic compound is solid, it exists as a giant ionic lattice, where positively charged cations and negatively charged anions are held in a lattice by strong ionic bonds and are not free to move around.

This means there is no possible movement of charge, so a solid ionic compound cannot conduct electricity. Why do ionic compounds conduct electricity when molten or in solution, but not when solid? In association with Nuffield Foundation. In this class practical, students test the conductivity of covalent and ionic substances in solid and molten states. This experiment enables students to distinguish between electrolytes and non-electrolytes, and to verify that covalent substances never conduct electricity even when liquefied, whereas ionic compounds conduct when molten.

The practical works well as a class experiment, with students working in groups of two to three. There will not be time to investigate all the substances, so each group could be assigned three or four of these, and the results pooled at the end.

The apparatus required for testing the conductivity of different substances when solid and molten. The covalent solids only need to be heated for a short time for melting to take place. The students should be warned about what to do if this happens eg cover with a damp cloth. The experiments should be done in a well-ventilated laboratory.

It may be helpful to reserve a crucible for each of the powdered compounds, while having one or two others that can be heated. Once a solid has been liquefied and allowed to cool, the solidified lump is often hard to break up or powder in the crucible.

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