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500 BCE
Aristotle
Aristotle did not believe the atomic theory. He believed that everything on earth was made up of the four elements, fire, water, air, and earth. -
500 BCE
Alchemy
Creation of a theory stating that all metals are made of mercury and sulfur. -
450 BCE
Democritus
He discovered that atoms were tiny particles that made up everything around us. At this time people thought he was crazy. -
1492
Columbus Arrives in America
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Robert Boyle
He was opposed to Aristotle's theory of elements. He believed that you could not simply split elements using chemistry. -
American Revolution
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John Dalton
He created the first solid atomic theory. -
Dmitri Mendeleev
Created a table of elements, categorized the elements into families. -
American Civil war
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J.J. Thomson
You can see electrons, and they are in atoms. Therefore you can see atoms. -
Robert Millikan
He was against the theory of electrons having charges -
Neils Bohr
He created the Bohr model of the atom, positive nucleus with negative electrons surrounding it. -
World War I
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Hans Geiger and Ernest Rutherford
Rutherford was the scientist who created the gold leaf experiments, while Geiger was his lab assistant. They shot an alpha particle at a gold leaf and determined that the atom has a thick could of electrons. -
James Chadwick
He discovered that neutrons have half the mass of an atom. -
World War II
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Hiroshima