Basic Electricity
Begin here, a general understanding.

Basic Electricity - Atoms and Electrons

Before we can understand electricity we have to know some things about atoms. At the core of all atoms is the nucleus. The nucleus contains one or more protons and may also contain neutrons. Protons have a positive charged and neutrons have no charge at all. Orbiting around the nucleus is one or more electrons. Electrons have a negative charge and are very small compared to protons and neutrons. The nucleus is very heavy compared to its electrons. As an example we'll look at the simplest of all atoms the hydrogen atom. The hydrogen atom has one proton and one electron. A hydrogen proton has a mass of approximately 1850 times the mass its an electron. Elements are classified by the number of protons they have. This is the atomic number. This is what differentiates the basic elements. For example, If an atom has one proton then its a hydrogen atom, if an atom has two protons then its a helium atom and an atom with three protons would be lithium. Copper has twenty nine protons. The atomic weight is the total number of protons and neutrons an atom contains.

Normally an atom has the same number of electrons as it has protons. When the number of electrons equals the number of protons the atom's total electrical charge is balanced or neutralized. If the atom loses an electron it has more protons than electrons and therefore its total charge is positive. If the atom gains an extra electron it contains more electrons than protons and has an overall negative electrical charge. When an atom has an imbalance of electrons and protons it is said to be ionized. An atom with a positive charge is a called a positive ion. An atom with a negative charge is called negative ion. A positive ion will exhibit an electron attraction while a negative ion will try to lose its extra electron

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