At one time, students used to be told: “We don’t know what electricity is, we don’t know how electricity goes through a solid wire,” etc. The electron theory explains these things clearly and simply. In addition, il explains the true meaning of voltage, resistance,  etc.

Therefore, an understanding of the electron theory is basic to the understanding of the electrical and electronic theory. Scientists now agree that our universe is basically dependent on two factors, one of which is matter, the other, energy. Matter is anything that occupies space and has weight. It can exist in any of the  three forms: solid, liquid or gas.

electrons & nucleus & protons & neutrons


Matter is composed of protons, neutrons and electrons. The proton has a positive charge. This component has very little weight. The neutron has no charge, but it supplies almost all the weight of matter. The electron has a negative charge. It also has very little weight.

If we could look at the structure of a piece of copper, we would find that it consists of a specific number of protons, neutrons, and electrons arranged in some particular way. In a piece of iron, a certain number of protons, neutrons, and electrons are arranged in a different way. The proton of iron is identical to that of copper and other elements.  They are all made up of the same components. It is the arrangement of these components that makes them different.

Electron Theory
Free Electron Theory


The electrons of an atom are arranged in shells around the nucleus. The electrons in the last shell are called ‘valence’ electrons and the electrical properties of a material are dependent on the number of such electrons. Atoms with less than four valence electrons give up one or more electrons, and the fewer the valence electrons, the easier this becomes. Atoms with more than  electrons in their last shell take one or more additional electrons.

The conduction of electricity is made possible by the free electrons in the outer shell.  Metals are good conductors of electricity as they have less than 4 valence electrons. These electrons aren’t strongly attached to the nucleus, but the ones in the inner shell are. Therefore, in a metal, they can move easily from one nucleus to another.


Electron Theory
Free Electron Theory of Metals

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