Basic Electrical Theory
ATOM AND ITS FORCES
There are two simple rules concerning electron shells that make it possible to predict the electron
distribution of any element:
The maximum number of electrons that can fit in the outermost shell of any atom
The maximum number of electrons that can fit in the next-to-outermost shell of
any atom is 18.
An important point to remember is that when the outer shell of an atom contains eight electrons,
the atom becomes very stable, or very resistant to changes in its structure. This also means that
atoms with one or two electrons in their outer shell can lose electrons much more easily than
atoms with full outer shells. The electrons in the outermost shell are called valence electrons.
When external energy, such as heat, light, or electrical energy, is applied to certain materials, the
electrons gain energy, become excited, and may move to a higher energy level. If enough energy
is applied to the atom, some of the valence electrons will leave the atom. These electrons are
called free electrons. It is the movement of free electrons that provides electric current in a
metal conductor. An atom that has lost or gained one or more electrons is said to be ionized or
to have an ion change. If the atom loses one or more electrons, it becomes positively charged
and is referred to as a positive ion. If an atom gains one or more electrons, it becomes
negatively charged and is referred to as a negative ion.