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Democritus
In 400 BC, Democritus reasoned that matter must be made of indivisible, small particles and named these small particles atomos. Video -
Lavoisier
Lavoisier hypothesized what is now known as the Law of Conservation of Mass. When he observed a chemical reaction, he realized the mass before the reaction was equal to the mass after the reaction, He then realized that mass was neither created nor destroyed, which is known as the Law of Conservation of Mass. Video -
Proust
Proust gave us the Law of Definite Proportion. He analyzed the compund of water and noticed that every compound of water was 89% oxygen and 11% hydrogen. Therefore, compounds always have the same proportion of mass. Video -
Dalton
Dalton was the father of the atomic theory. He used prior scientists' ideas and his own to come up with four major points about the atomic structure, even if some of his ideas were later proofed to be incorrect. His ideas were the foundation for later ideas about the atomic structure. Video -
Thomson
Thomson used a cathode ray in an experiment and discovered the existence of the electron. He also said that the electron had a negative charge. Video -
Millikan
Millikan discovered that the mass of an electron was essentially 1/1840 the mass of a proton. He did this through his oil drop experiment. Video -
Rutherford
Rutherford used his gold foil experiment to give us a nuclear model of the atom that is close to today's model and to make some new conclusions about the atom. He concluded that the atom is mostly empty space, it has a small dense center, and this small dense center, later called the nucleus, must be postivively charged. Video -
Chadwick
Chadwick discovered the existence of the neutron. He was observing neon and noticed that atoms of neon had different masses. He realized there must be a third particle with mass but no charge and this was named the neutron. Video
