jan 1, 1803 - John Dalton: Atomic Theory He proposed the atomic theory and stated that all matter is composed of small particles called atom; atoms of a given element has an identical size, mass and other properties; atoms cannot be cannot be destroyed, subdivided or created; in chemical reactions, atoms are separated, combined or rearranged; and atoms of different elements can combine in whole-number ratio to form a chemical compound.
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Date:
jan 1, 1803
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~ 223 years ago