Metals conduct because delocalised electrons are free to move through the structure
Definition
Delocalised electron
A delocalised electron is an electron that is not tied to one atom or bond and can move through part or all of a structure.
- A metal is a giant lattice of positive metal ions surrounded by a sea of delocalised electrons.
- Each metal atom releases its outer-shell electrons, and these become shared across the whole structure.
- Because they are not held to any single ion, the delocalised electrons are free to move throughout the metal.
- This movement lets the same electrons both carry electrical charge and transfer thermal energy.
- Everyday metals such as copper, Cu\text{Cu}Cu, and aluminium, Al\text{Al}Al, are used in wires and pans for exactly this reason.
Key Idea
- The same delocalised electrons are responsible for both electrical and thermal conduction in a metal.
- The mobility of these electrons links a metal's structure directly to how well it conducts.
Electrical conduction: delocalised electrons carry charge through the metal
Definition
Metallic structure
A giant structure of positive metal ions surrounded by delocalised electrons.
- Each electron carries a small negative electrical charge.
- When a metal is connected in a complete circuit, a potential difference pushes the delocalised electrons through the lattice.
- This flow of electrical charge in one overall direction is an electric current.
- Because a metal contains a huge number of mobile electrons, it is a good electrical conductor.
Common Mistake
- Do not say that the metal ions or atoms move to carry the charge.
- Always state that the delocalised electrons carry the electrical charge through the metal.
- Saying only that metals have 'free electrons' is not enough; you must say what those electrons carry.
Thermal conduction: delocalised electrons spread energy through the metal
Definition
Thermal energy
Energy associated with particles in a substance that can be transferred from hotter regions to cooler regions.
- When one part of a metal is heated, the delocalised electrons there gain kinetic energy and move faster.
- These fast-moving electrons travel through the metallic structure and collide with cooler particles further along.
- Each collision passes energy on, so thermal energy is transferred from the hot region towards cooler regions.
- Because their electrons move so freely, metals are good thermal conductors.
Example
- The metal base of a saucepan quickly carries thermal energy from the hob to the food.
- A metal spoon left in a hot pan soon feels hot because delocalised electrons transfer energy along it.
One structure, two kinds of conduction
Definition
Electrical charge
A property of particles that can be positive or negative and is carried through a metal by electrons.
- In electrical conduction, the delocalised electrons carry electrical charge through the metal.
- In thermal conduction, the delocalised electrons transfer thermal energy through the metal.
- Both properties come from the same feature: delocalised electrons that are free to move through the metallic structure.
Self review
- Which particles carry electrical charge through a metal?
- Why are delocalised electrons able to move through a metallic structure?
- How do delocalised electrons make a metal a good thermal conductor?
- What is an electric current in terms of charge?
- Why do both types of conduction depend on the same electrons?
