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Greek philosopher who lived between 470-380 B.C. He believed everything in the universe was made of atoms. Had no evidence to back it up. Thought atoms were microscopic and indestructible.
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Dalton was an English chemist. John Dalton's atomic theory said that all matter is made up of atoms. All atoms of an element were identical, different elements had different atoms.
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Thompson was an English scientist. Disovered the electron when experimenting with gas discharge tubes. There was movement in a tube. He called the movement cathode rays. The rays moved from the negative end of the tube to the positive end. He realized that the rays were made of electrons.
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Bohr was a Danish physicist. He proposed a model of the atom that is similar to the model of the solar system. All electrons have their energy levels- a certain distance from the nucleus. Level 1 can hold 2 electrons, level 2 can hold 8 electrons, level 3 can hold 18 electrons, level 4 can hold 32 electrons. The energy of electrons goes up from level 1 to other levels. When electrons release energy they go down a level. When electrons absorb energy they go to a higher level.
