Metals are good conductors of electricity because the delocalised…

The idea

Metals have a giant lattice of positive ions with a sea of delocalised electrons. These electrons are free to move, so when a potential difference is applied they drift and carry charge through the metal, giving high electrical conductivity. The same mobile electrons also transfer thermal energy: at the hot end they gain kinetic energy, move faster, and collide with other electrons and ions, passing energy along the metal. This explains why metals conduct heat well. For example, copper is used in electrical wiring and in cooking pans because its delocalised electrons allow both charge and energy to move rapidly. Insulators lack free electrons, so they do not conduct in this way.

What earns the marks

• Metals contain a lattice of positive ions surrounded by delocalised electrons.
• Delocalised electrons are free to move throughout the metal structure.
• In electrical conduction, delocalised electrons carry negative charge through the metal when a potential difference is applied.
• In thermal conduction, delocalised electrons gain kinetic energy at the hotter region and transfer energy by moving and colliding with other particles.
• The mobility of delocalised electrons explains both high electrical and high thermal conductivity in metals.
• Metals are used for electrical wires and heat exchangers because of these properties.

Common mistakes and how to put them right

• Thinking that positive ions carry the current in a metal.

  Put it right by stating that it is the delocalised electrons that move and carry charge; the positive ions only vibrate about fixed positions.

• Confusing electrical and thermal conduction mechanisms.

  Put it right by explaining that electrical conduction involves charge transfer by electrons, while thermal conduction involves energy transfer by faster-moving electrons colliding with other particles.

• Believing that heat travels through a metal as 'hot particles' moving from hot to cold.

  Put it right by describing energy transfer through collisions and electron movement, not bulk movement of ions.

Exam tips

• When explaining electrical conductivity, always mention delocalised electrons and their ability to move and carry charge.
• For thermal conductivity, link the kinetic energy of delocalised electrons to collisions that transfer energy through the metal.
• Use comparative language such as 'good conductor' and refer to the absence of free electrons in insulators to contrast behaviour.