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460 BCE
Democritus
held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible, and have always been and always will be in motion. -
Dalton
He discovered that certain gases could only be combined in certain proportions, even if two different compounds shared the same common element or group of elements. -
JJ Thomson
Discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. He realized that the accepted model of an atom did not account for negatively or positively charged particles. -
Rutherford
The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. -
Niels Bohr
He creates with Rutherford a system consisting of a small, dense nucleus surrounded by revolving electrons —similar to the structure of the Solar System, but with attraction provided by electrostatic forces rather than gravity. -
Schrodinger
Schrödinger 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.
