All matter is composed of indivisible elements called atoms
Lavoisier - Law of Conservation of Mass
John Dalton's Law of Partial Pressures
The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture.
Matter is simply composed of atoms of different weights and is combined in ratios by weight
JJ Thomson - Discovery and identification of the electron - “Plum Pudding Model”
Determined the charge to mass ratio of electrons
Ernest Rutherford - Discovery of Proton - "Gold Foil Experiment"
The atom must have a concentrated positive center charge that contains most of the atom's mass
Ernest Rutherford - Discovery of the Atomic Nucleus
An atom must contain a central nucleus
Niels Bohr - “Bohr’s model” -
Further developed Rutherford's nuclear atom model:
Energy levels of electrons are discrete
Electrons could only have certain classical motions
Electrons should move around the nucleus but only in prescribed orbits.
James Chadwick - Discovery of neutron
Neutrons are particles whose mass was close to that of a proton.