Electrons are critical to the workings of electricity (notice a common theme in their names?) In its most stable, balanced state, an atom will have the same number of electrons as protons. As in the Bohr atom model below, a nucleus with 29 protons (making it a copper atom) is surrounded by an equal number of electrons.

As our understanding of atoms has evolved, so too has our method for modeling them. The Bohr model is a very useful atom model as we explore electricity.

The atom’s electrons aren’t all forever bound to the atom. The electrons on the outer orbit of the atom are called valence electrons. With enough outside force, a valence electron can escape orbit of the atom and become free. Free electrons allow us to move charge, which is what electricity is all about. Speaking of charge…

## Flowing Charges

As we mentioned at the beginning of this tutorial, electricity is defined as the flow of electric charge. Charge is a property of matter–just like mass, volume, or density. It is measurable. Just as you can quantify how much mass something has, you can measure how much charge it has. The key concept with charge is that it can come in two types: positive (+) or negative (-).

In order to move charge we need charge carriers, and that’s where our knowledge of atomic particles–specifically electrons and protons–comes in handy. Electrons always carry a negative charge, while protons are always positively charged. Neutrons (true to their name) are neutral, they have no charge. Both electrons and protons carry the same amount of charge, just a different type.

A lithium atom (3 protons) model with the charges labeled.

The charge of electrons and protons is important, because it provides us the means to exert a force on them. Electrostatic force!

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