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400 BCE
Democratus
Democritus is most famous for being the first person to propose that atoms exist. He discovered the atom in 460–c.370 bc -
John Dalton
Dalton created the first chart of atomic weights. Seeking to expand on his theory. He discovered atom in 1803. Experiments with gases that first became possible at the turn of the nineteenth century led John Dalton in 1803 to propose a modern theory of the atom which he thought matter is made up of atoms that are indivisible and indestructible. -
JJ Thompson
He discovered electron in 1803. Development of the Atomic Theory. In 1897, J.J. Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. -
Ernest Rutherford
He conducted research that led to the first "splitting" of the atom in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered (and named) the proton. Rutherford became Director of the Cavendish Laboratory at the University of Cambridge in 1919. Used metal sheet and alpha particle to determine shape of unknown object. -
Niels Bohr
In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus
