THE VALENCE SHELL

After reading this section you will be able to do the following:

• Give an explanation of the valence shell of an atom.
• Explain what free electrons are and why they are important.

What is the valence shell?

Notice that in the copper atom pictured below that the outside shell has only one electron. This represents that the copper atom has one electron that is near the outer portion of the atom. The outer shell of any atom is called the valence shell. When the valence electron in any atom gains sufficient energy from some outside force, it can break away from the parent atom and become what is called a free electron.

Pictured here is an atom of copper, which is much more complex than either an atom of hydrogen or helium.

Atoms with few electrons in their valence shell tend to have more free electrons since these valence electrons are more loosely bound to the nucleus. In some materials like copper, the electrons are so loosely held by the atom and so close to the neighboring atoms that it is difficult to determine which electron belongs to which atom. Under these conditions, the valence or free electrons tend to drift randomly from one atom to its neighboring atoms. Under normal conditions the movement of the electrons is truly random, meaning they are moving in all directions by the same amount. However, if some outside force acts upon the material, this flow of electrons can be directed through materials and this flow is called electrical current. Materials that have free electrons and allow electrical current to flow easily are called conductors. Many materials do not have any free electrons. Because of this fact, they do not tend to share their electrons very easily and do not make good conductors of electrical currents. These materials are called insulators. There will be more information on this later.

Review

1. The valence shell is the outer shell of the atom.
2. Some materials have a free electron in their valence shell and this electron can easily move from atom to atom.
3. The free electrons are responsible for electrical current.