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AristotleBorn 384BC Died 322 BC. He believed that earth, wind, fire, and water, were the four elements. Tutor to Alexander the Great, Aristotle's theory lived on for a long time.
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Democritus Britannica Born 460 BC and Died 370 BC. He studied under Leucippus, and realized that because the world was changing so much, Space, had to exist. Space, also was made up of a neverending number of atoms, and was a vacum. These atoms were so small, they could not be seen with the naked eye. This, obviously, was a very radical idea for those times.
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Joseph PriestlyBorn March 13, 1733 and died February 6, 1804. Priestly discovered oxygen; disproving the theory attributing the four elements with the make-up of the Universe.
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Antoine LavoisierBorn August 6, 1743 and Died May 8, 1794. Lavoisier was starting to think about what an atom realy was. Lavoisier created the Law of Conversation, which states that matter cannot be made or destroyed, and that matter can be rearanged, but, again could not be destroyed.
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John DaltomBorn September 6. 1766, and died July 26, 1844. He believed that all the atoms of all the elements could be distinguished by their weights, His theory stated that
"All matter is composed of atoms
Atoms cannot be made or destroyed (rsc.org)
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are rearranged
and Compounds are formed from atoms of the constituent elements." -
Niels Bohr1815-1962
Niels Bohr made a model of the atom, in which he agreed that electrons orbit around the nucleus, and can change energy levels. He also won a Nobel Prize for Physics -
JJ Thomson (1856-1940)
Thomas discovered the electron, and claimed that an atom was "a sphere of positive matter in which electrons are positioned by electrostatic forces." (www.chemheritage.org/) -
Ernest RutherfordAugust 30, 1871, to October 19, 1967.
Rutherford's model of the atom stated that the nucleus was positive, and was orbited by negative nuetrons. He preformed many experiments, but the one that remain infamous is the "gold foil experiment".
