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Democritus was a Greek philosopher who lived in Abdera Thrace. Not much is known about his life, though it is believed that he was born around 460 BC, and died around 370 BC. Democritus was the first to suggest a form of atomic theory. He stated that all things are composed of “minute, invisible, indestructible particles of pure matter which move about eternally in infinite empty." At the time, there was no way to prove his theory, though we would later lean he was surprisingly accurate.
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Aristotle was a Greek philosopher who spent most of his live in Athens. There, he founded the school of philosophy known as the Lyceum. One of the things Aristotle is most well known for was his version of atomic theory. He suggested that all matter is made up of four elements: fire, air, water, and earth. Today, we know that his theory was incorrect. However, despite this, his theory persisted for over 2000 years.
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John Dalton was an English Chemist and Schoolteacher. In 1803, he built upon Democritus' theory, that all matter is made up of atoms which are too small to see, are uncuttable, and are indestructible. However, Dalton added to the theory, suggesting that all atoms of a given element are exactly alike, therefore atoms of different elements are different. John Dalton's theory ended a period of 2000 years, in which chemistry as a science was nonexistent.
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Michael Faraday was an English Chemist who lived in South London. He is well known or the discovery of electromagnetic induction. In 1831, Faraday discovered that atoms have an electrical component to them.
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Dmitri Mendeleev was a Russian Chemist. He was also the professor of chemical technology at the University of St. Petersburg. In 1869, Mendeleev created the first periodic table, in which elements were organized by their weights. His table was popular, partially due to the fact that the table actually left blank spaces for elements which were yet to be discovered.
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J.J. Thomson was an English Physicist. In 1897, he suggested that atoms were composed of even smaller substances. His model depicts negatively charged electrons, inside a positively charged "pudding."
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Ernest Rutherford was a British physicist, born in New Zealand. In 1911, he disproved J.J. Thomson's theory. He stated, that atoms are not a positively charged pudding filled with electrons, but rather that atoms have a small dense center called a nucleus, which are tiny in comparison to the rest of the atom. Most of the atom is just empty space where electrons move around. Though today his model has been improved upon, it is still seen as the classic idea of what an atom looks like.
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Niels Bohr was a Danish Physicist, who lived in Copenhagen. He built upon Rutherford’s theory. In 1913, Bohr theorized that electrons orbit the nucleus much like planets orbit the Sun. The electrons orbit the nucleus in several orbits, or shells, located at certain distances from the nucleus. For his contributions to science, Bohr received the Nobel Prize in Physics in 1922.
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Louis de Broglie was a French physicist. He is remembered for his monumental contributions to quantum theory. In his 1924 thesis, de Broglie stated that all electrons have a wave nature to them. He also suggested that all matter has wave properties. This theory answered problems to past theories which previously could not be answered.
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Erwin Schrödinger was an Austrian Physicist. He built upon de Broglie’s theory, assuming that electrons have a wave like behavior. In 1926, Schrödinger created his equation, which described how to find where an electron is likely to be at any given time in a 3 dimensional model. His equation could also accurately calculate the energy levels of electrons.
