The electrons in the outermost shell are called valence electrons. When enough external energy, such as heat, light, or electrical energy, is applied to the atoms of certain materials,
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.
| 23rd Nov, 2009,