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Democritus adopted the theory originated by his teacher, Leucippus. He created the first model of an atom, a circle with no protons, neutrons, or electrons. This helped the overall understanding of the atom for scientists.
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Lavoisier revolutionized chemistry. He named oxygen, carbon, and hydrogen, He also discovered that oxygen is involved in both combustion and respiration.
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Dalton's theory is still used today in modern chemistry. It was:
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.
John also visualized the atom as a sphere. -
Doing experiments with uranium salts, Becquerel discovers naturally occurring radiation.
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Thomson discovered the electron and created the Plum Pudding model. His discovery contributed to the understanding of the atom
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After experimenting and studying Becquerel's experiments, Marie and Pierre Curie discover and name two new metals, polonium and radium.
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In his landmark Gold Foil Experiment, Rutherford discovers a positively charged region that we now know as the nucleus.
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In 1909, Milliken created an Oil Drop experiment that helped quantify the charge of an electron, which helped out understanding of the atom and the atomic theory.
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In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits.
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Henry Moseley used X-ray to study atomic structure and his discoveries resulted in a more accurate positioning of elements in the Periodic Table.
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De Broglie's ideas eventually lead to the creation of the wave mechanics theory which gave us more knowledge of physical nature.
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In 1925, Pauli discovers that no two electrons can share the same quantum state at the same time.
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In an experiment, Chadwick discovers small neutrally charged particles, which we know today as neutrons.