As was pointed out in the introduction to this section, electronics are the use of the electrical charge to serve some function. That electrical charge is created at an atomic level through creation of positively and negatively charged ions. In a neutrally charged atom, having neither a positive nor a negative charge, there are an equal number of protons and electrons. In a negatively charged ion there are more electrons than protons. In a positively charged ion there are fewer electrons than protons. Take a copper atom for example. A copper atom has 29 protons. So when there are 29 electrons there is no charge as is shown below. When there are 30 electrons there is a negative charge. When there are only 28 electrons, there is a positive charge. Electricity, as we commonly think of it, is the flow of these electrons from one atom to another. The unit we use to measure this flow is called the Ampere or Amp which will be discussed along with Ohm's Law. The unit we use to measure electrical charge is the coulomb which we will discuss next.
The unit of coulombs is equal to the charge from a very large number of electrons. The symbol "C" is used to represent coulombs. Since we are not going to be counting electrons, its not all that important how many, but one coulomb is equal to the charge of 6.25 x 10^18 electrons. We will touch a little more on coulombs when we introduce other units such as Volts and Amps.
Conductors are materials that can easily give or receive free electrons. Free electrons are electrons not attached to an atom. These free electrons flow through conductors. Conductors are elements with fewer than 4 electrons in the outer layer. This outer layer is layer is called the valence layer. Electrons in the valence layer are called valence electrons. Copper, silver, and gold are all good conductors. Each has one valence electron.
If enough energy is applied, electrons can be freed from any material. However, insulators are materials that do not easily give up free electrons. Insulators have more than four electrons in the valence layer.
One of the most important parts of electronics, the semiconductor lies in between the conductor and insulator. Semiconductor materials such as silicone have four valence electrons. Semiconductors can be pushed to operate as both conductors and as insulators. We will discuss this more further in discussions on diodes and transistors.