Discoveries since Dalton's time have caused Dalton's original theory to be altered. Our modern Atomic Theory [local] is much more complex than the earlier theories of matter, but it completely explains the behavior of atoms for chemists.

The composition of the atom determines the chemical behavior and properties of the element. Early in the twentieth century the atom was shown to consist of protons and neutrons in the nucleus and electrons outside the nucleus [local].The subdivision of atom to this level is sufficient for most areas in chemistry. In the latter half of the twentieth century a finer structure of matter was developed. This is now called the Standard model and is needed to explain topics such as radioactivity. For this unit you will be concerned with the level of protons, electrons and neutrons. If you are unfamiliar with the concepts of quarks and bosons you might want to look at Course 03 which deals with the subatomic level of the atom in more detail. An excellent introduction for the standard model of matter can be found at The Particle Adventure.org.

Some links in this section were mirrored from original work by Dr. James Plambeck.