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400
Democritus
He came up with a theory that all matter is made out of invisible particles called Atoms. He said that Atoms are: solids that are indestructible, they are also homogenous. They are different in size, shape, mass, position, and arrangement. -
Dalton's Atomic Theory
He said: Matter is made out of Atoms that are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms. -
Joseph John Thomson
Thomson came to the conclusion that the deflection of the rays by electrically charged plates and magnets as evidence of quotbodies which are much smaller than atoms and quot that he calculated as having a very large value for the charge-to-mass ratio. -
Ernest Rutherford
Ernest Rutherford was responsible for discoveries in the fields of radioactivity and nuclear physics. He discovered alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. Most important, he found out the truth about the nuclear structure of the atom -
Niels Bohr
Better understanding of the structure of an atom and the early development of quantum mechanics. Quantum mechanics is physical theory of objects isolated from their surrounding. -
James Chadwick
He discovered neutrons which was important in the making of nuclear weapons.
