Classify each of the following as a conductor, semiconductor, or insulator. Air, Gold, Silicon, Rubber, Aluminum.

Conductors and Insulators

Conductors

As was shown in Figure 741.1.2, the nucleus of the copper atom

contains 29 protons. A neutral copper atom must therefore have 29

electrons distributed amongst its various shells. Shells k, 1, and m are

filled to capacity with a total of 28 electrons, so there is only one

electron in the n shell. The outermost shell of an atom, the n shell in

this case, is called the valence shell, and the number of electrons it

contains strongly influences the electrical properties of the element

that the atom represents.

figure 741.2.1 Free electron

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Since electrons in the valence shell are the farthest removed from

their nucleus, they experience the least force of attraction to the

nucleus. Coupled with the fact that electrons in a nearly empty shell

are easily dislodged from that shell, we find that the lone electron in

the valence shell of copper can readily vacate that shell. When an

electron breaks away from its 'parent' atom, it is called a free

electron, since it is then free to wander randomly through the

material.

An atom producing such a free electron acquires a net positive

charge, because its total number of protons is then one greater than

its total number of electrons. Such an atom is called a positive ion.

To become free, an electron must acquire enough energy to

overcome the force that binds it to its nucleus. In copper, there is

enough heat energy at ordinary room temperatures to liberate a vast

number of the weakly held valence electrons.