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400 BCE
Democritus
He theorized the existence of "atomos" as the precursor to atoms. He claimed that they acted as very small parts of an object that are inseparable physically, not geometrically, and they are specific to the material they occur in. He had no technology available to him to prove his theory. -
John Dalton
Dalton theorized that atoms exist, improving upon Democritus' theory, and claimed they had the shape of a ball as the nucleus and electrons had not yet been discovered. His theory was mostly speculation and no experiment was conducted to prove his theory. -
J.J. Thomson
He discovered the electron and proposed that atoms are like a "plum pudding" that contains a soup of electrons. He proved this using his cathode ray tube experiment. This ran light through a field of positive and negative metal plates in which the light would bend toward the negative plate. -
Ernest Rutherford
He discovers the nucleus as a group of protons and neutrons. He, with the help of Bohr, proposes the Bohr-Rutherford atomic model or the planetary model. -
Niels Bohr
He helped Rutherford develop the planetary atomic model by adding the electron orbits around the nucleus. His knowledge was not based upon an experiment but rather information from Rutherford and past research on mechanical electromagnetism. He states that the orbits allow electrons to revolve around the nucleus without releasing radiation. -
Werner Heisenberg
Most known for his uncertainty principle, which states that most attributes measured in physics can never be 100% accurate, and the theory of quantum mechanics. He measured the position of an electron using a gamma ray microscope. The more accurate the microscope, the more uncertain the momentum of the electron became. -
Erwin Schrodinger
He took the planetary model that Bohr and Rutherford had theorized and improved upon it by using mathematical equations to predict the likelihood of an electron in a certain position. This is the quantum mechanical model.
