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400 BCE
Democritus
Democritus was the first scientist to suggest that all matter was composed of small, indivisible particles and that the properties of matter was determined by the properties of these pieces of matter. -
John Dalton
Dalton was the first scientist to theorize that atoms of different elements had different weights and proposed a number of ideas about the atom that remains true today. -
J.J. Thompson
Thomson discovered the electron through a series of experiments. He concluded that electrons were much smaller than the actual atom and the charge to mass ratio was very large. Thomson also did experiments with cathode rays. -
Ernest Rutherford
Rutherford theorized that an atom had a very dense, positively charged core, due to particles being deflected by a sheet of gold foil, and that negatively charged electrons orbited the nucleus like planets around the sun. -
Neils Bohr
Bohr applied quantum theory to Rutherford's atomic structure involving orbiting electrons. Bohr concluded that electrons traveled in stationary orbits, but this also led to the discovery of energy levels and that there is a limited number of electron energies allowed. -
Erwin Schrodinger
Schrodinger, known for his quantum mechanical model, took the theories and ideas of other scientists before him and put them together to come up with his own equation. This equation proved that energy was quantized and that orbitals were essential to electron location. This equation explained chemical properties and reactivity of elements.