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http://www.youtube.com/watch?v=TgWn91ap99ADemocritus said that matter was composed of small particles called "atoms" that could be divided no further. His basic ideas were found in philosophical reasoning, not experimental testing. He called them atoms because in Greek "atomos" means indivisible.
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http://www.youtube.com/watch?v=dExpJAECSL8Made measurements of a chemical change in a sealed container. Lavoisier came up with the Law of Conversation of Mass. This law states that when a chemical reaction occurs, mass is neither created nor destroyed but only changes.
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http://www.youtube.com/watch?v=eQOTy6JUjEgA french chemist who observed that the composition of water is always 11% hydrogen and 89% oxygen by mass. Came up with the Law of Definite Proportions which states that compoounds have a consistent ration of elements.
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http://www.youtube.com/watch?v=07yDiELe83YThe father of the Atomic theory
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http://www.youtube.com/watch?v=XU8nMKkzbT8Experimented with a cathode ray tube and concluded that electrons are invisible negatively charged particles, and protons are invisible positively charged particles.
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http://www.youtube.com/watch?v=Q8RuO2ekNGwHe proformed the Gold Foil Experiment and came up with the plum pudding model of an atom. He said that the mass of an atom is positive and the dots are the negatively charged electrons.
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http://www.youtube.com/watch?v=XMfYHag7LiwProformed the Oil Drop Experiment and concluded the mass of one electron is 1/1840 the mass of a proton. Essentially the electron has no mass.
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http://www.youtube.com/watch?v=_nky2XQGQ3kProved the exsistence of the neutron
