Basic Electron Theory Digital Electronics TM 1.2 Introduction to Analog

Basic Electron Theory

This presentation will • Review the basic structure of the atom. • Define conductor, insulator, and semiconductor.

Basic Electron Theory

Digital Electronics

Structure of an Atom Conductor / Insulator / Semiconductor Example – Carbon Atom • The stability of the electrons in the outer ring determines Nucleus whether a material made from this element is a • 6 Protons - - • 6 Neutrons conductor, insulator, or semiconductor. Electrons • Elements whose electrons are unstable and can easily

- + + - move from one atom to another make good conductors. • Elements whose electrons are stable and can not easily Orbits move from one atom to another make good insulators. - - • Any elements that are not considered conductors or insulators are categorized as semiconductors. The distribution of electrons in the orbital rings around an atom’s nucleus determines the element’s electrical properties.

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Conductors Conductors: Example Ag & Cu • When an element’s outer electron ring is incomplete or not Silver Copper full, its electrons can move more freely from one atom to (Ag) (Cu) another atom. Because the outer-most band is incomplete, the • Elements whose electrons can move more freely make single electron is unstable good conductors. and loosely bonded to the • In general, most metals make good conductors because atom. Hence, it can easily move to the outer band of they only have one or two electrons in their outer band. 2 8 18 18 1 1 18 8 2 another adjacent atom. • Silver and gold are the best conductors. Copper is the second best conductor. Most wiring uses copper wire This free flow of electrons because it is a good conductor and is less expensive than is what makes silver and the other metals. copper good conductors.

5 Number of 6 Nucleus Electrons in Orbit

Insulator Insulator: Example Ne & Ar • When an element’s outer ring is complete, or full, its electrons can not easily move from one atom to another Neon Argon atom. (Ne) (Ar) The outer-most orbits of neon and • Elements whose electrons can not move freely make argon can each contain a maximum good insulators. of eight (8) electrons. This is exactly • Examples of good insulators are glass, plastic, rubber, how many they have. This makes the electron in the outer-most paper, or air. Most wiring uses plastic as an insulator. 2 8 8 8 2 bands stable. • Plastics are polymers or long chains of atoms bonded to one another. Viewing the atomic structure of plastics is This stable electron structure is far beyond the scope of this class (If you are interested what makes neon and argon good in such topics, you may want to take AP Chemistry.). insulators. • Neon and argon, both gases, are good insulators and are often used in light bulbs. 7 8

Semiconductor Semiconductors: Example C & Si • When an element’s outer ring is neither Carbon Silicon complete nor incomplete, the element is (C) (Si) considered to be a semiconductor. The outer-most orbits of carbon and • Examples of good semiconductor materials are silicon can each contain a maximum of eight (8) electrons. – Carbon (used to make resistors) Because they both contain four (4), these electrons are neither stable – Silicon (used to make transistors) 2 4 4 8 2 nor unstable.

This electron structure is what makes carbon and silicon good semiconductors.

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