The negative electrons, orbiting the positively charged nucleus of an atom, all try to get as close to the nucleus as they can. This is because opposite charges tend to attract each other. However, though no-one knows why, Quantum mechanics forces them to sit at fixed, or quantised, distances from the nucleus and only allow a limited number in each orbit level. Because of the link between the orbit and the energy, we tend to talk about the electrons sitting at various energy levels in the atom. The energy level furthest from the atom which still holds a fair number of electrons is called the valence level. This is because these are the electrons which provide most of the forces which 'stick together' solids and liquids, and control most chemical reactions. The level just above the valence level is called the conduction level. This is because electrons here help a material to be able to conduct electricity. When we remove an electron from the valence level (or one of the lower levels - nearer to the nucleus) we leave a hole. The atom now has an overall positive charge, so it looks a bit like we've added a positively charged particle to the atom. When we try to understand semiconductors, holes are very important. Engineers and solid-state physicists tend to talk about "holes moving from place to place" and "the velocity of the holes", etc. The holes don't really exist, but materials behave just as if they did. When a hole moves from atom A to atom B what actually happens is an electron moves from B to A. It looks just as though something positively charged went from A to B. 


Electricity is the movement of electrons through a conductor. Electrons are attracted to protons. Since we have excess electrons on the other end of the conductor, we have many electrons being attracted to the protons. This attraction sort of pushes the electrons toward the protons. This push is normally called electrical pressure. The amount of electrical pressure is determined by the number of electrons that are attracted to protons.

The electrical pressure or electromotive force (EMF) attempts to push an electron out of its orbit and toward the excess protons. If an electron is freed from its orbit, the atom acquires a positive charge because it now has one more proton than it has electrons. The unbalanced atom or ion attempts to return to its balanced state so it will attract electrons from the orbit of other balanced atoms. This starts a chain reaction as one atom captures an electron and another releases an electron. As this action continues to occur, electrons will flow through the conductor. A stream of free electrons forms and an electrical current is started.

This does not mean a single electron travels the length of the insulator, it means the overall effect is electrons moving in one direction. All this happens at the speed of light. The strength of the electron flow is dependant on the potential difference or voltage.

An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice. It is different from the positron, which is the antimatter analogue of the electron.

The electron hole was introduced into calculations for the following two situations:

1. If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors).
2. In crystals, band structure calculations lead to an effective mass for the charge carriers, which can be negative. Inspired by the Hall effect, Newton's law is used to attach the negative sign onto the charge.