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Democritus found the atom and he's the reason we know atoms today. He found out by breaking a "piece of matter" again and again and again until there's nothing left besides atoms. Without Democritus, we wouldn't know modern knowledge about atoms.
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Arisotle stated that all substances are made up of four elements: fire, water, air , and earth. To find this out Aristotle studies a lot like: philiosophy, ethics, physics, biology, psychology, and politics. He was a smart kid!
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John Dalton transformed Democritus's idea in to atomic theorys. Dalton's atomic theory is: 1. All matter is made up of tiny indivisable particles called atoms. 2. The atoms of the same element are identical, those of different elements are different. 3 Atoms of different elements combine in small, numerical ratios to form compounds. 4. Chemical reactions involve the rearrangment of atoms. No new atoms are breakable ( Law of Multiple Proportion).
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J. J. Thomson discovered the electron and conducted the cathode rays experiment. During his experiment, he found out by adding an electric charge he found that the moving pieces (durig his research) were electrons. On his model the electrons are set in a spere of positive material.
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Rbert's Major Controbution was that he determined the mass and charge of the electron. He also conducted oil drops by measuring the effect of an electric field on very small oil droplets. From the mass of the drop and the experiment on the plates, he calculated the charge on an electron.
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Ernest's discovery is that he found the nucleus and the atom is mostly (or 99%) empty or hollow. And that the atom contains a nucleus in the center of it.
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Bohr's Major Contribution was that an electron is found only in specific paths, or orbits, around the nucleus.
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Sir James Chadwick didn't do anything special, but he confirmed the existence of neutrons in the nucleus. He also confirmed more things as well that other people discovered.
