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John Dalton was an English chemist that transformed Democritus's ideas on atoms into a scientific theory. He studied the ratios in which elements combine in chemcial reactions. Dalton came up with theories to explain the observations that he had in his expiraments in 1803. This is how Dalton's atomic theory was created. The theory states that elements are composed of identical indivisable atoms. Multiple atoms can become mixtures and compounds but one cannot change into a different atom.
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J.J. Thomson, an English physicsist discovered the electron and determined the charge-to-mass ratio of an electron. He passed electric current through glass tubes sealed with gas. A source of electricity was connected to the electrodes of which one had a positive charge and one had a negative charge he soon had an attraction and created the cathode ray. Then he deflected it with a magnet.
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He discovered the atomic nucleus. He did this by shooting a beam of tiny positively charged particles at thin metal foils. The major deflections were caused by the alpha particles being repelled by something small, dense, and positive inside the atoms of the foil. Thus he created the atomic nucleus.
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Milikan was a U.S. physicist who found the charge carried by an electron. Using this and the ratio found by Thomson, he found the mass of an electron. He balanced the downward gravitational force and the upward charge on tiny drops of oil that were suspended between two metal electrodes.
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Bohr proposed that the electron moves in a circular orbit at fixed distances from the nucleus.
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French physicist Louis de Broglie suggests that moving properties lik electrons have properties of waves. After a few yaers experimental evidence supports the hypothesis,
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He develops mathematic equations to describe the motion of electron in atoms which leads to the electron cloud model.
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The English physicist confirms the existence of charge-less neutrons. The belief is that nuclei contain neutrons and positively charged protons.
