Nearly free electron model

Imagine you have a lot of tiny ball-like things called atoms. Sometimes, these atoms get together and form a material, like a metal. Inside these materials, some electrons are not stuck to any particular atom, they can move around very easily.

Scientists noticed that the outer electrons of these atoms can move freely within the metal. They acted as if they were moving around in a sea of electrons. Scientists call this the nearly free electron model.

This explains how electricity and heat can move through the metal. When electricity closes a circuit through a metal, the electrons in the metal start moving to create a current. When the metal is heated, the free electrons bump around more, and the energy from this bumping is transferred throughout the material.

So, when we talk about the nearly free electron model, we refer to the idea that electrons in some materials move around freely and allow the flow of electricity and heat.