9.0 EFFECT OF AN ELECTRIC CURRENT ON SUBSTANCES

Why can copper wires carry electricity safely, but if you put a live wire into salt water, something dramatic happens? Why are new cars coated in chrome, and how is aluminium extracted from its ore? The answers lie in understanding how different substances behave when an electric current passes through them. This chapter explores conductivity in solids and liquids, the process of electrolysis (breaking down compounds with electricity), and its vital applications in electroplating and extracting reactive metals.

9.1 CONDUCTIVITY IN SOLIDS AND LIQUIDS

Substances conduct electricity if they have charged particles that are free to move. In solids, these particles are usually electrons. In liquids, they can be electrons (in liquid metals) or ions (in molten or dissolved ionic compounds).

9.1.1 Conductivity in Solids

• Metals (e.g., copper, aluminium, iron): Good conductors. They have a structure of positive ions in a "sea" of delocalized electrons. These electrons are free to move throughout the metal, carrying charge.
• Graphite (carbon): A non-metal that conducts electricity. Each carbon atom forms three bonds, leaving one electron delocalized. These free electrons move within the layers, allowing conduction.
• Other non-metals (e.g., sulfur, plastic, wood): Insulators. They have no free electrons or ions; all electrons are tightly bound in bonds.
• Ionic compounds (solid state): Do