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Democritus found that atoms are not all the same, they are eternal, and always moving. He made a theory on this to explain why and how atoms were so small, and what they were about.
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Dalton found the atomic weight, and chemical symbols, and discovered proportions of elements in compounds.
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J.J. Thomson discovered electrons, and then said the atom was a sphere of positive electricity, with negative particles throughout it.
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Rutherford discovered the atomic nucleus. He used a thin foil made of gold metal to find positive and negative charges in an atom.
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Bohr's atomic model shows a positively charged nucleus surrounded by electrons.
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He figured out the structure of the atom, and their radiations, and started the basis of quantum theory.
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Erwin Schrödinger and Werner Heisenberg discovered the electron cloud model. They said an atom consists of a dense nucleus and many proton and neutrons and is surrounded by electrons, but they all have different energy levels, and different charges.
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He discovered the neutron when alpha waves bounced off of them and they showed no charge.
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Rutherford said the atom is mostly empty space with a nucleus that has a positive charge surrounded by negative electrons. Then Bohr said they circulate the atom.
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Aristotle discovered that matter is made up of atoms, and that it cant be created or destroyed. He also found that there are four elements, from which he came up with the theory of motion.
