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THE FREE ELECTRON

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

• Explain how electrons are arranged in an atom.
• Describe how elements maintain their electrical balance.

Maintaining electrical balance

Each basic element has a certain number of electrons and protons, which distinguishes each element from all other basic elements. In most elements, the number of electrons is equal to the number of protons. This maintains an electrical balance in the structure of atoms since protons and electrons have equal, but opposite electrostatic fields.

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

The copper atom has 29 protons in its nucleus with 29 electrons orbiting the nucleus. Notice that in the copper atom, the electrons are arranged in several layers called shells. This is to graphically represent that the electrons are at different energy levels within the atom. The energy of an electron is restricted to a few particular energy levels. The energy is said to be quantized, meaning that it cannot vary continuously over a range, but instead is limited to certain values. These energy levels or shells follow a very predictable pattern. The closest shell to the nucleus can have up to 2 electrons. The second shell from the nucleus can have up to 8 electrons. The third shell can have up to 18 electrons. The fourth shell can have up to 32 electrons, and so on. Atoms can have this many electrons, but they do not have to have this many electrons in each shell. The greater distance between the electrons in the outer shells and the protons in the nucleus mean the outer shell electrons experience less of a force of attraction to the nucleus than do the electron in the inner shells.

In the next sub-unit you will learn about the the outer shell of an atom called the valence shell.

Review

1. Atoms have their electrons arranged in layers called shells.
2. In order to maintain electrical balance the number of electrons is equal to the number of protons in most elements.