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The Greek Model
- Contributed to the atomic theory by naming the smallest unit of matter and atom. Atom means "indivisible."

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- He didn't believe in atoms. He believed that was only made up of fire, water, earth, and air.

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Atomic Theory
- Believed that atoms of the same element are exactly alike and that atoms of different elements are different.
- He also believed that atoms of different elements combine to form compounds.
- Said that atoms are too small to see and they are indestructible.

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Plum Pudding Model
- Had a theory that there are small, negatively charged particles inside an atom called electrons.

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The Nuclear Model
-Discovered that Atoms contain mostly empty space.
- Learned that there is a small, dense, positively charged nucleus.
- Figured out that electrons are scattered around the nucleus at a distance.

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The planetary Model
- Figured out that energy levels are located at certain distances from the nucleus
- Bohr also learned that the electron location depends on how much energy it has
- Discovered that electrons travel in paths called energy levels

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- Chadwick discovered the neutron
- Proved Rutherford's theory that most of the mass is in the atom's nucleus

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- Electrons are found in electron clouds, not in paths.
- Electrons move around the nucleus billions of times in one second.