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400 BCE
Democritus
Democritus thought that if you kept cutting a stone it would be so small that it would be indivisible. He called the small piece of matter "atomos" -
300 BCE
Aristotle
Aristotle believed that everything was a combination of water, fire, earth, and air. There were no separate particles for each material, it was all one. -
Antoine Lavoisier
He 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 Louis 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. -
J. Thomson
Used a CRT to experimentally determine the charge of mass ratio of an electron. 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 Bhor
Bhor 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. -
Werner 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
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
Using alpha particles discovered a neutral atomic particle with a mass close to a proton Thus discovered the neutron. -
Murray Gell-Mann
Classified particles and their interactions. He proposed that the observed particles are comprised of smaller building blocks.