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A greek philosipher by the name of Democritus first had the thought that everything was made out of atoms. He believed that atoms were inseperable, that they were so small you could not make them any smaller. He also thought that there was air in between each of the atoms.
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John Dalton was an English scientist, who first thought of the Atomic Theory. Dalton called his theory the "Billiard Ball Model." Dalton believed that all matter was made up of atoms and that all atoms were both invisible and indestructable.
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J.J. Thomson was a british scientist who first doubted Dalton's original theory. Thomson thought that there were smaller paricles inside of the atom. This theory made another, that atoms could also be divided. Thomson discovered that positive and negatively charged particles would attaract. All of this was shown with the "plum pudding model".
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Ernest Rutherford was a student of Thomson. Rutherford knew all about the "plum pudding model" & decided to try it out. Ruthherford tested the model and saw something. That something couldn't be explained by the "plum pudding model". Rutherford then presented a new idea, What if there was a small dense positive place, called the nucleus. Rutherford did more work to calculate the nuclei's diameter was 100,000 times smaller than that of the gold atom.
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James Chadwick discovered the nuetron. He figured out the atomic number was determined by how many protons were in the shells. Before all of this James Chadwick had had a lingering suspicion an atom wsn't all it seemed to be. He had thought it had some other smaller part; hence the nuleus.
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The Modern Model is the ever improving model. It is the woked the from 1920 and how it's changed over he years.
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Borh had a a theory that the electrons were supposed to move around the nucleus in organized orbits. The theory that Bohr came up with could have given an explaination of why the atoms emitted the light while they were in fixed wavelengths.
