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The Alchemists were based on the belief that everything in the universe was created by four elements and the ideas proposed by the ancient greeks. The four elements they believed made up the world were water, fire, air, and earth.
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The estimated time where the ancient greeks made most of their discoveries is not agreed on by everyone but it is said that they made most of their findings around 400 BCE. The Ancient Greeks discovered that everything in the world is made up of these tiny things called atoms and also proposed the idea that everything is made up of the four elements.
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John Dalton claimed that all the atoms in elements were identical, but depending on the element presented the atoms could vary in size and mass.
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Thomson discovered that all atoms contained little negatively charged particles and electrons. Thomson was also the one who created the plum pudding model. Most of his discoveries were made around 1897
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Hantaro is most commonly known for his "Saturnian" system in 1904
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Rutherford found out in 1907 that some substances have half-lives Rutherford also found a flaw in Thomson's model back in 1911. He figured out that the atom had a small but heavy nucleus. After Rutherford found this out he created a new model and names it the "Rutherford model"
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Around the time 1913 Bohr gave a theory that electrons should be moving around the nucleus but not freely, in a certain orbit. Going from a higher energy orbit to a lower one. Bohr also created a new model to show the shells and orbit of the elections
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Planck was a German physicist who was the originator of the quantum theory. Which is a theory that helped old chemists and physicists understand more about the atomic and subatomic process'
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Aston is known currently for his major discovery of isotopes, which are molecules that have the same formula but have a different structure. He found this by the use of a mass spectrograph.
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Einstein probably had one of the biggest contributions to the atomic theory by proposing the idea of gravitation. He also proposed the general theory of relativity. It is said he made most of his discoveries between the years of 1916 and 1921
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Around 1926 Schrödinger took Bohr's model one step further by using his knowledge in math to determine an equation to describe the location of an electron in a certain position.
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Bose is known for his work on quantum mechanics which was the foundation for the Bose-Einstein statistics
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The greatest contribution that Heisenberg had to the atomic theory was that he discovered that there is no way of knowing the position and momentum of a particle at the same time.
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Pauli discovered in the Bohr model that no two electrons in an atom could have the same set of quantum numbers and created his own principal called the "Pauli Principal"
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Louis De Broglie figured out how the wave nature of elections work and he also proposed the idea that all matter has wave properties
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Chadwick discovered that atoms had something else in the center of it called neutrons. He figured out that neutrons didn't have a positive or negative charge but still contributed to the weight of the atom as much as protons did.
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Hodgkin figured out the molecular structure of penicillin, insulin, and vitamin B12.
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Rosalind Franklin discovered the molecular structure of coal and carbon which were later used to develop strong carbon fibers and more. She also discovered molecular structures of DNA, RNA, and Virus' which gave important information that we use to this day.
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Fermi is most commonly known for his experiments in the first-ever chain reaction. He did this by releasing energy from the nucleus of the atoms.
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Leroy was famous for the development of the Leroy-Bernstein Theory. He was also interested in the intramolecular forces, he defined and analyzed the basic forces between atoms and molecules.
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Bader discovered how important the electron density really is for explaining how the behavior of atoms works.