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460
Democritus
During 460 BC democritus discovered the atomic theory,a scientific theory of the nature of matter -
John Dalton
john dalton made three main discoveries
all substances are made of atoms
atoms join with other atoms to make new substances
atoms of the same element are exactly alike and atoms of different elements are different -
J. J. Thomson
A century later in 1897, J. J. Thomson made a discovery that required a revision to the atomic theory. Using a cathode-ray tube he discovered that a positive plate would attract an invisible beam. He concluded that this beam must contain particles that have a negative charge. He called these particles corpuscles, but today they are called electrons. -
Ernest Rutherford
- In 1909, Ernest Rutherford was surprised by the results of his experiment. In it he aimed positively charged particles at a thin sheet of gold foil. Most of the particles passed right through the sheet, but some were slightly larger or even - went back. In 1911, he revised the atomic theory
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Niels Bohr
In 1913, Niels Bohr discovered that electrons travel around the nucleus in definite paths. These paths are located in levels at certain distance from the nucleus
