The atomic theory was a theory based on the idea that every item in this world could be broken down into an extremely small particle called the atom. If the idea had never been presented and recorded, then there would have been no attempts to prove it, and science would have suffered as a result.
Dealing with the events before the birth of Christ, the only significant scientific development was in sixth century B.C. It was the discovery of static electricity by rubbing a piece of amber against fur and observing that the fur stood on end. Thalleus of Maletus believe that this power was derived from the amber, not to any particle. A man by the name of Democritus thought it was something else two centuries later. He believed that all matter was permanently divisible into eensy-beensy particles called atoms that had statical electric properties (Atoms).
We now enter a period called the Dark Ages. If events ever took place, they were not recorded. Let us now jump into our time machine towards 1803.
In 1803, John Dalton theorized that if all atoms exist, they must follow the Law of Conservation of Mass and the Law of Proportions. His beliefs were published as "The Atomic Theory." The five postulates were: All matter has definite particles called atoms, atoms are indestructable, atoms of one particular element are identical, and when atoms combine they make more complex particles (Dalton's Atomic Theory).
Even though it is not chronologically correct, a few modern add-ons to this Atomic Theory would be appropriate. Two additions are: There are three subatomic particles: protons, neutrons, and electrons. The second addition states that the nucleus is the center of all the subatomic particles (Modern Atomic Theory).
In 1896, the proton was observed by E. Goldstein. Upon reading this report, a man named Joseph Thomson instantly became fascinated by this and devoted his time to solely the Atomic Theory.