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Democritus first comes up with the idea that all matter is made of particles, or atoms.
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John Dalton discovers the first useful atomic theory, based on the law of conservation of mass, and the law of constant composition
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William Crookes discovers a fourth state of matter, which led to modern electronic theory, by charging electricity through a gas in a sealed tube
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Henri Becquerel discovered radiation through investigating fluorescence in uranium salts
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J.J Thomson discovered electrons by using a cathode ray tube
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Ernest Rutherford discovers that atoms have a dense nucleus, which contains protons, with the gold-foil experiment.
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Niels Bohr introduces the theory that electrons move around the nucleus of an atom in orbits, and introduced the idea that an electron could move from a higher energy orbit to a lower energy one
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It was discovered that electrons move in orbitals, in different levels. The Electron Cloud Model is the model currently being used today.
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James Chadwick discovered the neutron by bombarding elements with alpha particles
