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Democritus
(442 BC) He was the first to propose that the smallest particles were atoms. He imagined splitting something in half, then in half again, and again, and questioned when it would end. However, Aristotle disapproved of this idea, and no one ever thought about this for 2000 years -
Isaac Newton
Newton propsed that the universe contained many of those small particles, these particles were always in motion. -
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Atomic Theory Timeline
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John Dalton
John Dalton was the a scientist to propose a theory that all atoms were shaped like spheres, however they all have different properties. The spheres would vary in size, mass and/or color. Dalton used the model to explain that all matter is made of small, indivisble particles called atoms, that all atoms of an element are identical in size and mass, that different elements have different properties, and that different elements can only combine in specific ratios in order to form new substances. -
Joseph John Tomson
While experimenting with different beams of particles, he observed that different elements produced the same type of beam, causing him to believe that all atoms contain smaller particles that are identical. His model of an atom was a sphere of positive charged particles surrounding negatively charged ones. -
Ernest Rutherford
Rutherford released postively charged particels trhough a thin sheet of gold foil. Some particles bounced back, got sharply defected, or passed through. This caused Rutherford to fix Thomson's atomic model, and make his own, with a postively charged nucleus and bouncing electrons. -
Albert Einstein
Albert Einstein contributed to basically all aspects of science. He used the Brownian motion theory proposed by Robert Brown to reinforce his theory and prove that atoms existed -
Neils Bohr
Bohr proposed the most widely used model of the atom. He drew the electrons on specific "energy levels." He proposed this because he saw how light was released by hydrogen atoms in a tube. He also said that under normal circumstances, electrons would not fall below the lowest energy level or touch the nucleus. -
Francis William Aston
Aston was able to observe the seperation of isotopes of neon with the use of electromagnetic focusing, He noticed that there were very little differences in mass between isotopes. He continued to extend this principle and came up with 212 naturally occuring isotopes
