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Democritus
Democritus had a guess about what small pieces of matter were but no evidence was found. -
Dalton
Dalton concluded that evaporated water exist in air as an independent gas. He is known as the "father of modern theory". He performed experiments mostly by mixing gases and observing the outcomes. -
Goldstein
He noticed that the cathode rays were emitted perpendicular with respect to the surface of the cathode on the contrary to the shafts which propagate in all directions. He ascertained that the concave cathode (of the bowl shape) emitted the cathode rays which all focused in one point. He also proved that the features of that rays were not due to the material of which cathode was made. Moreover the cathode rays can induce the chemical reactions which are normally caused by the sun light. -
Thomson
Thomson discovered electrons and isotopes. He performed an experiment in a cathode ray tube and observed what happened in it. His model looked like raisin bread and is known as the "plum pudding" model. -
Rutherford
This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through thin metal foils and detecting them using screens coated with zinc sulfide. Rutherford found that although the vast majority of particles passed through. -
Bohr
Bohr improved Rutherford's atomic model. He added that fixed orbits (energy levels) travel around the nucleus. -
Chadwick
In this experiment, alpha particles are projected towards beryllium target. The emitted particles are allowed to fall on paraffin wax, which in turn releases another type of particles. The study of the properties of such particles showed that they are protons. From the energy calculations, Chadwick showed that the particles released from beryllium, as a result of the incidence of alpha particles on it, are uncharged and have the same mass as protons. He called them neutrons. -
Schrodinger
Erwin Schrodinger made a profound discovery in 1927 by showing that the discrete energy states of matter could be determined by Wave Equations. Significantly, these allowed frequencies corresponded to the observed discrete frequencies of light emitted and absorbed by electrons bound in atoms/molecules. This further confirmed the standing wave properties of matter, and that only certain standing wave frequencies could exist which corresponded to certain energy states.
