Some stuff I am studying tonight....

By adding energy, such as heat or light, it is possible for a valence orbit electron to absorb this energy and move into the valence orbit of a neighboring atom. An electron freed from its valence state is called a free electron. Because a single cubic inch of copper contains approximately 1.4 x 10 to the power of24 free electrons, a veritable cloud of free electrons moves about in a piece of copper. An atom that has lost one or more valence electrons has a net positive charge and is called a positive ion. This concept of free electrons is extremely important, because free electrons make an electric current possible.

As an electron moves from the valence orbit of one atom into the valence orbit of another atom, it leaves behind a space that it used to occupy. This space is often referred to as a hole. By definition, a hole is the absence of a negative electron and cannot be electrically neutral. Consequently, holes are considered to be positively charged and equal in magnitude to the negative charge of an electron.

I feel like I should have went to my science classes!