Though we credit Dalton with the invention of the atomic theory, he was not the one who formulated the three principles stated in the theory. The atomic theory has three main ideas. They are as follows.
1. All matter is made up of atoms.
2. Atoms are indestructible and cannot be divided into smaller particles.
3. All atoms of one element are exactly alike, but they are different from atoms of other elements.
Each one of these principles was developed by a scientist other than Dalton.
The first idea was theorized by the early Greek philosopher Democritus between 460-370 B.C. He proposed that all matter in the world was made up of tiny particles called atoms. Though he had no way to prove his theory, he was correct in his ideas.
The second factor of Dalton’s atomic theory was discovered by the French chemist Antoine Lavoisier in 1782. Lavoisier found that matter could not be created nor destroyed. He proved this by conducting a chemical reaction in a sealed container. Before he started, he measured the reactants (substances that go into the reaction). When the reaction was finished, he measured the products (substances that come out of the reaction). He found that the mass of the reactants and products were equal. We know call this principle the law of the conservation of mass (or matter).
The third principle of the atomic theory came in 1782 and was discovered by a French chemist named Joseph Proust. He observed that proportions of elements in compounds were always the same in each specific compound. For example, no matter where water is obtained, it will always contain 11 percent hydrogen and 89 percent oxygen. If the flavor of water is different depending on its source, it is merely because the water contains different dissolved minerals. However, the minerals do not become part of the water. This property of matter was named the law of definite proportions.
When Dalton proposed his atomic theory in 1803, he had accumulated the discoveries of Democritus, Lavoisier, and Proust and combined them into a theory. He made a few modifications. He reasoned that if matter was indestructible, atoms must be indivisible. We now know he was incorrect in this theory. Atoms can be destroyed; they release huge amounts of energy when this happens. He also took the law of definite proportions and applied it to elements instead of compounds.
Dalton’s atomic theory has served as a basis for the study of chemistry. Though it was written in 1803, it has remained essentially intact to the present day.