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400 BCE
Democritus
He made the first atomic hypothesis. His theory was that everything is made of "atoms". -
Period: 400 BCE to
Timeline of Models of the Atom
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330 BCE
Aristotle
Thought that all elements on Earth were not made of atoms except for Earth, Fire, Water and Air, themselves. -
500
Alchemists
Said that all metals were formed from two principles — mercury and sulfur. -
1492
Columbus Arrives in America
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Robert Boyle
He believed everything was composed of tiny particles. Stated that the volume of a gas decreases with pressure. -
American Revolution
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John Dalton
Said that all matter is composed of atoms. -
American Civil War
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Dmitri Mendeleev
Created the periodic table. -
J. J. Thompson
Discovered the electron, and did experiments regarding atomic theory. -
CRT
Discovered that all atoms contain negatively charged subatomic particles (electrons). -
Plum Pudding Model
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The Oil Drop Experiment
Determined the magnitude of electron charge. -
Robert Millikan
Showed electrons having a discrete, quantifiable charge. -
Ernest Rutherford
Put forth the idea of a tiny, dense, positively charged core called a "nucleus". -
Gold Foil Experiment
Discovered most of the atom is empty space around the nucleus. -
Rutherford Planetary Model
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Hans Geiger
Stated nucleus has all the positive charge and mass of an atom. -
Neils Bohr
Developed Bohr model and hydrogen atom theory. -
Bohr Model
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World War I
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James Chadwick
Discovered the neutron. -
World War II
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Hiroshima
