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460 BCE
Democritus
Democritus was a "central figure" when it came to the development of the atomic theory. His theory was that all materials are made up of invisible, small atoms. He conducted an experiment of taking a seashell and breaking it in half. He continued to break each half into another half. Eventually he had nothing left but powder and he could not longer split it in half. He was the first to discover the indivisible "building block" of an atom. -
Antoine Lavoisier
Antoine Lavoisier developed a theory based off of experiments about chemical reactivity of oxygen as well as the modern naming system for chemicals. Lavoisier did a lot in his time. He proposed the combustion theory, named oxygen, and proposed the Law of Conservation of Mass. He worked with phosphorus and sulfur majority of the time. The two elements burned quickly together which is out he found out that they gained weight when combined with air. -
John Dalton
John Dalton proposed the Law of Multiple Proportions. This law led to Dalton establishing the very first useful atomic theory of matter. In addition to this, Dalton developed the concept of the mole and a "ground system" to show atoms and other elements. John Dalton also hypothesized that sizes of particles making up different gases must be different. This idea was derived from several experiments. -
J.J. Thomson
J.J.Thomson is known for discovering the electron by experimenting with a cathode ray tube.He saw that cathode rays were charged negatively.He also studied the particles that were positive in neon gas.He identified that the accepted part of the ion didn't account for positive and negative particles.To see if the charges were separate,he used a magnet to bend the cathode rays away from the electrometers.He then concluded that the electric charge from the ray must be combined rather than separate.
