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Aristotle Aristotle believed all matter was made of "The Four Elements".
1) Fire
2) Earth
3) Air
4) Water He didn't have any proof to support his theory. Although, people still believed and supported him becaue at that time Aristotle was one of the greatest minds. -
Democritus Atomic Theory Democritus come up with the theory stating that matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. This piece would be indivisible. He named the smallest piece of matter “atomos,” meaning “not to be cut.”
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Dalton's Theory John Dalton proposed an "atomic theory" with sphere shaped, solid atoms based on the properties of mass. 1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. -
Sir William Crookes Sir William Crookes discovered the element Thallium. He is also known for his cathode-ray studies.
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J. J. Thomson Sir Joseph John Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vaccum cathode-ray tube.
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The Curies discovered polonium (Po) and Radium (Ra).
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Ritherford proved that atoms of one radioactive element would turn into another, by expelling a piece of the atom at high velocity.
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Niels Henrik David Bohr proposed adding to the Bohr model to fix mistakes.
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recognition of Ernest Rutherford for the radioactive element
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Millikan determined the electric charge carried by a single electron.
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Erenst Rutherford discovered the atomic nucleus and developed a model of the atom.
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Henry Moseley discovered the systematic reaction between wavelength and atomic number
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Moseley was shot dead during the Battle of Gallipolli in Turkey.
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Robert Andrews Millikan designed the photoelectric effect (Albert Einstein).
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Bohr's proposal was correct , he recieved the Nobel Prize for his work.