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Democritus
He proposed that all matter, including space and time, was made up of small units named atoms. he did no experiments and had little evidence, but his ideas was kept on by Lucretius. -
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Democritus' Model
Model of the atom was a solid indestructible sphere. -
Dalton
Agreed that all matter was created by atoms, which he believed were indestructible. He also stated that compounds are created by combining two atoms, and that all atoms of given elements are identical in their mass and properties. -
Dalton's Model
Said the atom was a solid, indestructible sphere -
J.J. Thomson
Discovered the electron. he experimented by testing and studying the nature of electric discharge in a high vacuum cathode-ray tube. -
Cathode Ray Tube
Cathode Ray Tube Video
In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles, which he calculated must have bodies much smaller than atoms and a very large value for their charge-to-mass ratio. -
Thomson's Model of Atom
In this model, the atom is composed of electrons (which Thomson still called "corpuscles", though G. J. Stoney had proposed that atoms of electricity be called "electrons", in 1894[1]) surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding". -
Rutherford
Discovered the nucleus and protons in the atom. Used the gold foil experiment to discover the modern model of the atom. He concluded that all positive charges were centralized, while negative electrons orbited the nucleus. -
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Millikan
Used an oil drop experiment to determine the charge of a single electron. -
Rutherford's Model
Rutherford's 1911 analysis, that the so-called "plum pudding model" of J. J. Thomson of the atom was incorrect. Rutherford's new model[1] for the atom, based on the experimental results, contained the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and with this central volume also containing the bulk of the atomic mass of the atom. This region would be named the "nucleus" of the atom in later years. -
Bohr
Explained that outer orbits in an atom could hold more electrons than the inner orbitals. By knowing this, one can determine the atom's chemical properties. He also gave birth to the ideas that electrons emit light by jumping orbitals. -
Bohor's Model
Introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity. -
Chadwick
Discovered the neutron. The neutron helps balance out protons in the nucleus of an atom. -
Chadwick's Model
Chadwick's discovery was significant for the fission of uranium 235 since neutrons do not need to overcome any Coulomb barrier, unlike positively charged alpha particles, which are repelled by the electrical forces present in the nuclei of other atoms, and neutrons can therefore penetrate and split the nuclei of even the heaviest elements.
