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Period: 460 BCE to 370 BCE
Democritus
he was a greek philosopher who came up with the atomic theory -
Period: 384 BCE to 322 BCE
Aristotle
he did not believe in the atomic theory and taught otherwise. -
Period: to
John Dalton
he pioneered the modern atomic theory -
Period: to
JJ Thomson
he discovered the electron in 1897 he also studied positively charged particles in neon gas.