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400 BCE
Democritus
Democritus believed that if you kept cutting something, such as stone, that it would become so small that it would be indivisible. He called that small piece of matter atamos. -
300 BCE
Aristotle
Aristotle believed that all matter was a combination of air, water, fire and earth. He believed there were no separate particles for each material, it was all one. -
Antoine Lavoisier
Lavoisier proposed the Combustion Theory, which was based on sound mass measurements. He also proposed the Law of Conversation of Mass which represents the beginning of modern chemistry. -
Joseph L Proust
Proust proved that the relative quantities of any given pure chemical compounds elements remain invariant, regardless of the compounds force. This is known as the law of definite proportions. -
John Dalton
Dalton proposed an atomic theory with spherical solid atoms based upon measurable properties of mass. -
Joseph J Thompson
Thompson used a CRT to experimentally determine the charge of mass ratio of an electron. He also studied canal rays and found they were associated with proton H+ -
Ernest Rutherford
Rutherford studied radiations emitted from uranium and thorium and named them alpha and beta. -
Neil Borh
Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined equations. Electrons should move around the nucleus but only in prescribed orbits. -
Warner Heisenberg
Heisenberg created the theory of quantum mechanics. For this theory and the applications of it which resulted especially in the discovery of allotropic forms of hydrogen. -
Erwin Schrodinger
Schrodinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. -
James Chadwick
Chadwick, using alpha particles, discovered a neutral atomic particle with a mass close to a proton. The result of this is that he discovered the neutron. -
Murray Gell-Mann
Gell-Mann classified particles and their interactions. He proposed that the observed particles are comprised of smaller building blocks.