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450
Democritus
Proposed that matter exists in the form of a particle -
John Dalton
Proposed the atomic theory based on measured masses -
Dmitri Mendeleev
Created the first periodic table -
Ernest Rutherford
Found that the nucleous was small, dense , and positivley charged -
William Crookes
Discovered that cathode rays travel in straight lines, and made Crookes tube -
JJ Thomson
Discovered the electron -
Ernest Rutherford
Alpha particles are doubly ionized helium atoms -
Niels Bohr
Atoms have orbital shells with electrons -
James Chadwick
Discovered the neutron