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In 440 B.C. Democritus, a Greek Philosopher hypotesized about all matter being able to be broken down into tiny invisble particles until they couldn't be broken down any further, but the idea wasnt popular because there wasn't any experimental evidence to support his theory.
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In the 1800's Dalton reconsidered Democritus' thoery and reasoned that each element is composed of a different atom and came up with the basic atomic theory:
1) All matter is broken down into particles called Atoms
2) Atoms of different elements have different properties
3) Atoms of different elements can be combined in ways to create new substances
4) Atoms of the same element are identical in properties such as size/mass. -
JJ Thomson theorized that atoms might be made of smaller, charged parts and that atoms must be made of both positive and negatives: Electrons (-) and Protons (+).
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During his research of the atom, Rutherford conducted an experiment and discovered that inside the atom was a nucleus
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In 1913, Neils Bohr discovered that the tiny particles (electrons) travelled in energy levels surrounding the nucleus and completed the model of the atom.
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Rutherford's student, Chadwick discovered the neutron particles in the nucleus of an atom; neutrons are particles that are neutrally electric charged particles.
