|  | 4.1 | Basics of Electricity
| 4.1.4 |

Electrical current including insulators, conductors, and semiconductors

Atoms, or groups of atoms called molecules, can be referred to as materials. Materials are classified as belonging to one of three groups, depending on how easily electricity, or free electrons, flows through them. Electrical Insulators Electrical insulators, or insulators, are materials that allow electrons to flow through them with great difficulty, or not at all. Examples of electrical insulators include plastic, glass, air, dry wood, paper, rubber, and helium gas. These materials have very stable chemical structures, with orbiting electrons tightly bound within the atoms.

Electrical Conductors
Electrical conductors, or conductors, are materials that allow electrons to flow through them with great ease. They flow easily because the outermost electrons are bound very loosely to the nucleus, and are easily freed. At room temperature, these materials have a large number of free electrons that can provide conduction. The introduction of voltage causes the free electrons to move, causing a current to flow.

The periodic table categorizes some groups of atoms by listing them in the form of columns. The atoms in each column belong to particular chemical families. Although they may have different numbers of protons, neutrons, and electrons, their outermost electrons have similar orbits and behave similarly, when interacting with other atoms and molecules. The best conductors are metals, such as copper (Cu), silver (Ag), and gold (Au). All of these metals are located in one column of the periodic chart, and have electrons that are easily freed, making them excellent materials for carrying a current.

Other conductors include solder (a mixture of lead (Pb) and tin (Sn), and water with ions. An ion is an atom that has more electrons, or fewer electrons, than a neutral atom. The human body is made of approximately 70% water with ions, which means that it, too, is a conductor.

Electrical Semiconductors
Semiconductors are materials where the amount of electricity they conduct can be precisely controlled. These materials are listed together in one column of the periodic chart. Examples include carbon (C), germanium (Ge), and the alloy, gallium arsenide (GaAs). The most important semiconductor, the one that makes the best microscopic-sized electronic circuits, is silicon (Si).

Silicon is very common and can be found in sand, glass, and many types of rocks. The region around San Jose, California is known as Silicon Valley because the computer industry, which depends on silicon microchips, started in that area.

Whether materials are classified as insulators, conductors, or semiconductors, it is the knowledge of how each one controls the flow of electrons, and of how they work together in various combinations, that is the basis for all electronic devices.

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