Electrical conductivity is one of the defining properties of metals and distinguishes them from most non-metallic materials. The reason metals conduct lies in the nature of metallic bonding at the atomic level.

Metallic Bonding

Metal atoms have relatively few electrons in their outermost electron shell, and these outer electrons are held quite loosely compared with electrons closer to the nucleus. When metal atoms come together in a solid, these outer electrons are released from individual atoms and become shared across the whole metal structure. The result is a regular lattice of positively charged metal ions surrounded by a mobile sea of electrons that does not belong to any particular atom.

The Free Electron Sea

The delocalised electrons in this free electron sea are not fixed to any atom. They can move freely throughout the metal in response to any applied electric field. When a battery or other voltage source is connected to a metal wire, it creates an electric field along the wire. The free electrons, being negatively charged, experience a force from this field and move toward the positive terminal, creating an electric current.

The more easily electrons are delocalised in a metal, the better its conductivity. Silver is the best electrical conductor of all the elements, followed by copper, gold, and aluminium. These metals have structural characteristics that allow particularly free electron movement with minimal collisions and energy loss.

Resistance

As electrons move through the metal, they occasionally collide with the vibrating metal ions in the lattice. These collisions slow the electrons slightly and cause them to transfer some energy to the lattice in the form of heat. This is the origin of electrical resistance and the reason wires heat up when carrying significant current. Higher temperatures cause more vigorous vibration of the lattice ions, which increases the frequency of collisions and therefore increases resistance, which is why most metals become less conductive as their temperature rises.

Summary

Metals conduct electricity because metallic bonding produces a sea of delocalised electrons that can move freely through the metal lattice when a voltage is applied. The free electrons carry the electric current. Resistance arises from collisions between moving electrons and the vibrating metal ions. Higher temperatures increase resistance by increasing collision frequency. Silver and copper are the best electrical conductors due to their particularly free electron mobility.