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In 1932, James Chadwick pealed beryllium atoms with alpha particles, which produced an unknown radiation that became known as neutrons. Chadwick referred to this radiation as being embodied of particles with a neutral electrical charge and the approximate mass of a proton.
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The first one to discover the electrons in 1897. He referred to his theory as the Plum Pudding where he said that the Plums were the negatively charged parts that get attracted to the positively charged parts or what he referred to as Pudding. In case of the same parts getting together, they repulse.
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In 1908, Robert Millikan discovered the electric charge of the electron. (Timeline) He reached this conclusion when he performed the oil-drop experiment. (Quizlet)
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Believed that all matters of an elements are identical, but different elements has different sizes and composed of atoms that are inadvisable.
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In 1905, Albert Einstein concluded that different particles make up light. Also, he created the theory of relativity.
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Today's model is based on the Quantum Model/Wave Model of the atom. The model is based on wave mechanics techniques. This states that an atom is mostly empty space, contains a very small nucleus, and electrons move in an electron cloud. (Notes)
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In 1913, Neils Bohr stated that electrons move from energy levels and orbit around the nucleus.
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Democritus
Believed that all atoms were small, hard particles that were all made of the same material but were different shape and size.
Aristotle
He believed that everything is made of air, fire, earth, and water.

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In 1908, Ernest Rutherford performed the Gold Foil Experiment where he built a gun that shot alpha particles at gold foil, and observed the reactions. He essentially discovered the nucleus when the alpha particles occasionally bounced back off the foil. He concluded that the small positively charged core of atoms was a nucleus. He came up with the nuclear model of the atom.(Notes)
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