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John Dalton thought that each element was made up of atoms that are all alike. Dalton imagined atoms as tiny, solid balls.
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JJ Thomson discovered the electron. He proposed a new model, it was a posatively charged sphere with electrons embeded in it.
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Ernest Rutherford concluded that the atom is mostly empty space and electrons orbit around a posatively charged nucleus.
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Niels Bhar proposed a model where the electrons move in specified layers instead of randomely.
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James Chadwick discovered the existence of the neutron.
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Electrons form a negatively charged cloud around the nucleus.