Question

Why does an ionic compound conduct an electric current when the compound is melted but not when it is in the solid state?

Short answer

An ionic compound conducts an electric current when melted but not in the solid state because in the solid state, the ions are held tightly in a rigid crystal lattice structure by strong ionic bonds, restricting their movement. However, when melted, the lattice structure breaks down, freeing the ions to move. This allows the compound to conduct an electric current in its liquid state as the mobile charged particles (ions) can flow in response to an electric field or potential difference.

Step-by-step solution

1. Understanding ionic compounds

Ionic compounds are formed when a metal donates one or more of its valence electrons to a non-metal, resulting in the formation of positive metal ions (cations) and negative non-metal ions (anions). These oppositely charged ions are held together by electrostatic forces called ionic bonds.

2. Ionic compounds in the solid state

In the solid state, ionic compounds form a rigid crystal lattice structure where the ions are held together tightly by the strong ionic bonds. These ions are not free to move, thereby restricting the flow of charge through the compound.

3. Ionic compounds in the liquid state

When an ionic compound is melted, the crystal lattice structure breaks down as the ionic bonds weaken. The heat energy applied to melt the compound provides the ions with enough energy to overcome these bonds and move freely within the liquid. In the liquid state, the ions are able to move and become more mobile.

4. Requirements for conduction

For a substance to conduct electric current, it must possess two critical properties: charged particles that can move (electrons in metals or ions in electrolytes) and an energy source to drive these charged particles through the substance (usually an electric field or a potential difference).

5. Conclusion

An ionic compound cannot conduct an electric current in the solid state because the ions are held tightly within the crystal lattice structure by strong ionic bonds, restricting their movement. However, when the compound is melted, the lattice structure breaks down, and the ions are free to move. This allows the compound to conduct an electric current in its liquid state as it now has mobile charged particles (ions) that can flow through the material in response to an electric field or potential difference.