Explaining Conductivity (Edexcel IGCSE Chemistry)

• Electric current is the flow of charged particles
  • This usually refers to electrons, but it could also mean the flow of ions
  • Collectively, they can be termed freely moving charged particles

• Most covalent compounds do not conduct electricity as they have no freely moving charged particles to carry the current
• They act as insulators and have many applications which rely on that property
• Covalent substances are used as electrical insulators in solid, liquid and gaseous form
  • For example, sulfur hexafluoride is a dense gas used to insulate electrical transformers
  • Silicone oils and liquid hydrocarbons are also used in electrical equipment

• Common insulators include the plastic coating around household electrical wiring:

Covalent compounds are used as insulating materials

• There are some exceptions to conductivity in covalent compounds
  • Organic polymers have been developed which have multiple adjacent double bonds that allow electrons to migrate along the length of the polymer chains
  • These unusual materials have potential uses as electronic components and biomedical applications

• Ionic compounds can conduct electricity in the molten state or in solution as they have ions that can move and carry charge
• They cannot conduct electricity in the solid state as the ions are in fixed positions within the lattice and are unable to move

• During electrolysis the electrons move from the power supply towards the cathode
• Electron flow in electrochemistry thus occurs in alphabetical order as electrons flow from the anode to the cathode
• Positive ions within the electrolyte migrate towards the negatively charged electrode which is the cathode
• Negative ions within the electrolyte migrate towards the positively charged electrode which is the anode

Diagram showing the direction of movement of electrons and ions in the electrolysis of NaCl