Theme 2: Energy and the Environment Background Material

Basic Atomic Structure

Atomic theory
The atomic theory of matter, first postulated by John Dalton, is the basis of all modern chemistry. As stated by Dalton, the atomic theory of matter consists of three postulates:

1. Each chemical element is made up of very small particles called atoms.

2. All of the atoms of a given element are identical. The atoms of one element are different from the atoms of any other element in some fundamental way.

3. Atoms combine with each other to form compounds. A given compound always has the same relative numbers of different types of atoms.

The atomic theory of matter holds that atoms are the fundamental units of matter and that atoms are conserved in chemical reactions. In other words, chemical reactions consist of rearrangements of atoms to form compounds while the atoms themselves remain unchanged.

In 1911, Ernest Rutherford showed that the mass of an atom is concentrated in a very small central portion of the atom which is called the atomic nucleus. The atomic nucleus is made up of nucleons, of which there are two important fundamental types: electrically positive protons and electrically neutral neutrons. Orbiting the atomic nucleus are the electrically negative electrons. The electrons shown below do not orbit the nucleus in the same way as the planets orbit the sun. Electrons are actually found in "clouds" but it is easier to picture as if they were temporarily stopped.

Copper Atoms

The most common metal used in electrical wiring today is copper. Copper is an element with an atomic number of 29. This means that it has 29 positively charged protons in its nucleus and 29 negatively charged electrons orbiting the nucleus. Even when totally neutral, metals such as copper contain vast quantities of mobile electrons. The copper wire contains a vast quantity of particles with "charge." However, the net charge is zero because there are an equal number of protons and electrons.