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John Dalton
Common substances always broke down to the same elements with the same proportions. Atoms cannot be created or destroyed. His model showed that each chemical element is composed of atoms of a single, unique type. -
JJ Thomson
His experiment involved cathode ray tubes that showed that all atoms contain tiny negatively charged subatomic particles or electrons. His model was the "plum pudding" model, a model that showed a majority positive atom with "floating" electrons. -
Ernest Rutherford
He shot alpha particles at gold foil and proved that: 1. Most alpha particles travel through the foil undeflected which shows that the atom is mostly empty space. 2. Some alpha particles are deflected by small angles which shows that the nucleus and the alpha particles are positively charged. Occasionally, an alpha particle travels back from the foil which means the nucleus is most of the atoms mass. His model was an atom with a nucleus with electrons scattering around it. -
Niels Bohr
Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. -
James Chadwick
Discovered nuclei have neutron which have no charge. Isotopes of the same element have the same number of protons and electrons but differ in the number of neutrons found in their nucleus.