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Not until around 460 B.C., did a Greek philosopher, Democritus, develop the idea of atoms
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The Solid Sphere Model was the first atomic model and was developed by John Dalton in the early 19th century. He hypothesized that an atom is a solid sphere that could not be divided into smaller particles.
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In 1900 Max Planck, a professor of theoretical physics in Berlin showed that when you vibrate atoms strong enough, such as when you heat an object until it glows, you can measure the energy only in discrete units. He called these energy packets, quanta.
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Thomson’s model was known as the "Plum Pudding Model” (or "Raisin Bread Model.") As each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons, these were the “plums” in the pudding. Thomson suggested that the positive fluid held the negatively charged electrons in the atom because of its electrical forces.
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Rutherford proposed that atoms consisted of a small dense center filled with positive charges. He then said that negatively charged electrons were scattered surrounding this dense, positively charged center. He stated these negatively charged electrons were held in orbit by the positively charged nucleus, due to the electrical forces.
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In 1912 a Danish physicist, Niels Bohr came up with a theory that said the electrons do not spiral into the nucleus and came up with some rules for what does happen.
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Bohr’s atom like Rutherford’s contained a dense, positive nucleus. He expanded on Rutherford’s ideas, turning his attention to describing the electron. He stated they moved in fixed, circular orbits (or energy levels) around the nucleus, these called electron shells.
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Not until 1919 did Rutherford finally identify the particles of the nucleus as discrete positive charges of matter
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In 1924 a Frenchman named Louis de Broglie thought about particles of matter.
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The quantum mechanical model is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time.
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1932 did the English physicist James Chadwick finally discover the neutron
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In 1960, Murray Gell-Mann and Yuval Neman independently proposed a method for classifying all the particles. The method became known as the Eightfold Way. In 1964 Gell-Mann went further and proposed the existence of a new level of elementary particles and called them "quarks"