The Evolution of Atomic Theory

There were many ideas on the atom in the earlier days. In ancient Greece there were two main philosophers that had two different ideas on the atom. Democritus believed that all matter is made of small indivisible particles called atoms, and all atoms are exactly alike. Aristotle, however, believed that all matter was continuous. His ideas were under speculation, but accepted for 2000 years. In the 1800’s an English schoolteacher, John Dalton, reasoned that elements were composed of atoms and that only whole numbers of atoms can combine to form compounds. He also believed that elements represent different kinds of atoms with different properties. He then found that atoms (which are indivisible and indestructible) also get rearranged in reactions. This goes along with the Law of Conservation of Mass because the law states that: Mass is neither created nor destroyed by chemical or physical changes, and in his discovery he found that atoms get rearranged in reactions which would keep the mass the same. In 1897 J. J. Thompson made piece of equipment called a cathode ray tube which he found where and what the electrons of the atom were. He called the atom the plum pudding model. He also found protons and neutrons in the atoms as well. Ernest Rutherford was another English physicist. He conducted the “Gold Foil Experiment”. In the experiment he used radioactivity. By using the model he found out that atoms are mostly empty space, and they are small, dense, with a positively charged nucleus. All of the scientists helped us now understand more about atoms, and their structures. They gave the world new ideas, and added to the atom theories.