In an insulator, the valence electrons are tightly bound to the nucleus and do not move freely. This means that there is a large energy gap between the valence band and the conduction band. In order for an electron to move from the valence band to the conduction band, it must absorb a large amount of energy. This makes it difficult for electricity to flow through an insulator.

Conductor

In a conductor, the valence electrons are loosely bound to the nucleus and move freely. This means that there is a small energy gap between the valence band and the conduction band. Even a small amount of energy can cause an electron to move from the valence band to the conduction band. This makes it easy for electricity to flow through a conductor.

Bohr-Rutherford Model of Atoms

The Bohr-Rutherford model of atoms shows that the electrons orbit the nucleus in fixed circular paths called shells. The electrons in the outermost shell are called the valence electrons. The number of valence electrons determines whether an element is an insulator or a conductor.

Elements with a large number of valence electrons, such as sodium and chlorine, are good conductors of electricity. This is because the valence electrons are loosely bound to the nucleus and can easily move from the valence band to the conduction band.

Elements with a small number of valence electrons, such as diamond and rubber, are poor conductors of electricity. This is because the valence electrons are tightly bound to the nucleus and cannot easily move from the valence band to the conduction band.