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400 BCE
Democritus' Discovery of Atoms
Democritus proposes the theory of all things being made up of tiny particles he names "atomos," meaning uncuttable.
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Antoine Lavoisier's Conservation of Matter
Antoine Lavoisier introduced the idea that matter cannot be created or destroyed in a chemical reaction, and the mass of matter does not change after the chemical reaction.
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Proust's Definite Proportions
Joseph Proust's law of constant composition details that compounds will always contain the same ratio of elements.
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John Dalton's Atomic Theory
John Dalton proposed the theory that all matter is made up of tiny indivisible particles known as atoms.
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J.J Thomson's Discoveries
The most prominent of Thomson's discoveries were the electron and the Plum Pudding Model, named after a popular English dessert. The Plum Pudding Model closely resembles the American chocolate chip cookie.
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Albert Einstein's Photoelectric Effect
Albert Einstein observed the shedding of electrons when electromagnetic radiation, like that of light, hits a material. Einstein labeled these discharged electrons "photoelectrons."
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Rutherford's Discovery of the Nucleus
When conducting an experiment where alpha particles were directed at a sheet of gold foil, he noticed some particles glancing off of the sheet. Upon doing further research, he discovered the nucleus of the atom where it had been assumed was empty space.
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Niels Bohr's Atomic Model
Nearly 16 years since the Plum Pudding Model was introduced Niels Bohr produced a new model supporting the idea of an atom as a miniscule, positively charged nucleus surrounded by orbiting electrons.
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Rutherford's Discovery of the Proton
Nine years after first discovering the atom's nucleus, Rutherford persevered to uncover more about the tiny particles comprising our world. After noticing his scintillation detectors identified hydrogen nuclei in the air, Rutherford found they were produced from already-present nitrogen atoms. Upon further examination, Rutherford concluded all nuclei must contain protons.
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Louis de Broglie's Discoveries
Among the many of De Broglie's innovations, the most notable are matter waves and the Quantum Model. De Broglie built off of Bohr's Model, determining electrons travel in a loose, wavy pattern rather than a rigid elliptical orbit.
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Chadwick's Discovery of the Neutron
By 1924, the atom was known to have a central core containing protons with electrons revolving around it in an irregular fashion. What more was there to be known? In May 1932, James Chadwick released his discovery of an uncharged particle present in the atom's core, which he called the neutron.
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