Democritus :
Democritus 460BC – 340BC Composed the theory that everything is composed of atoms
John Dalton:
John Dalton 1803, composed the Atomic Theory All matter is composed of atoms Atoms cannot be created or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements
JJ Thompson:
JJ Thompson 1897, Discovered the electron by deflecting cathode rays with magnetic fields 1913, Discovered isotopes while experimenting with canal rays.
Max Planck:
Max Planck German physicist who came up with the quantum theory. In the 1900s, he showed that energy is emitted and absorbed in discreet packets of “quanta” and that these had a definite size
Albert Einstein:
Albert Einstein Disovered the Photoelectric effect In 1905, he discribed how the photoelectric effect was caused by absorption of a quanta of light.
Robert Millikan:
Robert Millikan American experimental physicist In 1908, he performed the oil drop experiment to discover the actual charge of an electron
Ernest Rutherford:
Ernest Rutherford 1909, proved was a very small positively charged particle in the center of the atom. Found this by performing the Geiger – Marsden experiment.
Niel Bohr:
Niel Bohr 1913, describes the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbit around the nucleus Solar System Model Composed energy levels for electrons in the atom.