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400
Democritus
His Theories: (465 BC)
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement. He was the one who discovered the atom in 460 BC -
John Dalton
Discovered the atomic theory of matter around 1803 He performed a series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole -
J.J. Thomson
He thought cathode rays were particles with a negative electric charge and much smaller than an atom -
Robert Milliken
He measured the charge on an electron -
Niels Boh
He realized that Rutherford's model wasn't quite right. By all rules of classical physics, it should be very unstable. Bohr suggested the revolutionary idea that electrons "jump" between energy levels -
James Chadwick
In 1932 Chadwick proved the existence of neutrons. He used a different method for tracking particle radiation and knocked the protons out of the nucleus. But the nucleus still had some mass, what proved that neutrons exist.
