Each element is made of tiny particles called atoms.
Atoms of a given element are identical. Atoms of different elements are different in some fundamental way
Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative number and type of atoms.
1898-1903 – JJ Thomson (cathode ray experiment)
Found when high voltage is applied across the 2 metal nodes in the cathode ray tube a negatively charged beam was produced.
Led to the plum pudding model of the atom that consisted of a positively charged cloud with negative electrons embedded in it randomly.
1909 – Robert Millikan (oil drop experiment)
Determined charge and mass of electron using oil droplets between charged plates
1911 – Rutherfords metal foil experiment
Determined there must be a large positive mass at the center of the atom
