Basic Electricity Knowledge Part 2

Basic Electricity - Band Theory

The electrons of the atoms orbit in energy levels or bands. As the number of electrons increase through the different elements the bands are filled in a predictable order. The innermost band (band one) is filled first when its full then band two is populated then band three and so on. Band one can hold two electrons. Band two can hold eight electrons. Band three can hold eighteen electrons. Band four can hold eight electrons. I won't go any further. The last band that contains electrons in an atom is called the valance band. The first unfilled level above the
valence band is known as the conduction band. The bands further from the nucleus Have gradually greater energy levels.

Electrons in the valence band do not participate in the conduction process. They have to be in the conduction band. The farther the electron is from the nucleus and the fewer neighbors an electron has in the valance band the smaller the gap is between the valance band and the conductive band. This means less energy is required to move it to the conduction band where it then becomes a free electron and is able to participate in the conduction process. This energy can be room temperature heat. In metals the gap is non existent and the valance band and the conduction band overlap slightly. This means that the valance electrons are constantly meandering between the two bands making them excellent conductors. Insulators, on the other hand, have an energy gap that is far greater than the available energy of the electron. A conductor has sufficient free electrons in the conduction band to allow an electrical current to flow when a potential difference is applied. In an insulator all the electrons lie in the valance band and the energy gap is too large for electrons to occupy available higher energy levels when a potential difference is applied. However if a very high voltage is applied to an insulator the the electrons will be able to bridge the forbidden gap and make it to the conduction band. Effectively making the insulator a conductor. This is called insulation breakdown. A semiconductor is a material whose conductive properties make neither a good conductor nor a good insulator.