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4000 BCE
Decritus
He proposed that all matter was made up from small indestructible units called atoms. -
John Dalton
Proposed that atoms were responsible for the combinations of elements found in compounds.
We now know that atoms of the same element are not completely identical. But it still we consider it the smallest particles. -
Electrical charges
Experiments with electricity showed up that atoms were not solid spheres but were composed of smaller bit called subatomic particles, which were proton, electron, and neutron -
J. J. Thomson
He applied electricity to electrodes sealed in a glass tube, which produced streams of small particles called cathode rays. He proposed the "plum-pudding" model for the atom in which potions were randomly distributed.
We now know this model is not the correct atomic model, because the protons are not randomly distributed. -
Ernest Rutherford
He worked in Thompson to test his model. In Rutherford`s experiment, positively charged particles we're aimed at a thin sheet of gold foil. According to Rutherford, it was as though he had shot a cannonball at a piece of tissue paper, and it bounced back at him. -
Niels Bohr
His model was the first that incorporated quantum theory and was the predecessor of wholly quantum-mechanical models. The Bohr model and all of its successors describe the properties of atomic electrons in terms of a set of allowed (possible) values. Atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states.
