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400 BCE
Democritus
All matter consisted of extremely small particles that could not be divided -
Dalton
All elements are composed of atoms
All atoms of the same element have the same mass.
Compounds contain atoms of more than one element -
Thomson
The atoms spread throughout the matter -
Rutherford
Atoms positive charge is concentrated in its nucleus. -
Bohr
A description of the arrangement of electrons in an atom is the centerpiece of modern atomic model
