For much of the time until the last century, it was considered that electricity was some kind of fluid. Likewise it was thought that all substances can be divided into arbitrarily small parts. It turned out that there is a limit to this division and so the atomic theory was conceived. We will review here its key concepts.
Atomic theory describes atoms as made up of three different components.
In the centre of an atom there is a small and dense nucleus, made up of protons and neutrons . There is normally quite a few of them, and the number of protons is roughly similar to that of neutrons. Substances are made up of various atoms, which differ in their number of protons. An important point for us is that the proton has a special property called charge . Charge is a basic quantity underpinning all electrical phenomena.