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Greek philosopher Leucippus and his student Democritus were studying matter when they developed a theory. They believed that the matter was made of tiny particles that were so small they could not be cut in half. They gave these particles the name Atomos which means uncuttable. There theory on atomos (or atoms) came from the idea that if something is cut in half enough times, it can no longer be split.
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This law discovered/proposed by Lomonosov states that matter neither increases nor decreases in a closed system. This means, that for reactants and products, the number of atoms (and type) must be equal.
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Dalton proposed that substances would always break down into the same elements. He believed that the combinations of these elements were atoms.
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J.J. Thomson first discovered the electron in 1897. In his Plum Pudding Model, Thomson used plums to portray negativley and postivetly charged electrons packed together making an atom.
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Neils Bohr, also Thomson's student, suggested that electrons orbit the nucleus at set distances and energies.
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Ernest Rutherford, J.J. Thomson's student, discovered the nucleus by shooting molecules at gold foil. He noticed that most passed through, but some bounced off. This meant that atoms contained mostly empty space. He also found a high concentration of meolecules at the center of the atom. THis he named the nucleus.
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Heisenberg suggested that it is impossible to determine the exact speed and position of electrons.
