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440 BCE
Democritus' Theory About Atoms
Democritus proposed his theory that everything is made up of tiny particles that was surrounded by empty space and can even vary in size and shape because of the substance it makes up. -
Period: 440 BCE to
The Atomic Theory Timeline
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John Dalton's Discovery
John Dalton found that common substances always broke down into the same elements and the same proportions. He even concluded that the various compounds were combinations of atoms of different elements that could not be created or destroyed. -
J.J. Thomson's Discovery of Electrons
Thomson discovered the electron in 1897. He created a model that showed a sphere that was packed with positive matter and negatively charged electrons. -
Ernest Rutherford's Discovery
Rutherford wondered about Thomson's model so he decided to shoot alpha particles at a gold foil. Most of it went through the foil, but some bounced back. He concluded that atoms are mostly empty space and that the particles went through the empty space. The rest hit the nucleus and bounced back. -
Niels Bohr's Theory
Bohr developed a theory that electrons were sort of like the solar system model. Electrons are at fixed distances and have the same energy.However, some experiments shown the electrons moved in waves. -
Werner Heisenberg Discovery
Heisenberg said that it is impossible to determine the speed and location of an electron around an atom. This gave birth to the quantum model.