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Democritus believed matter could not be divided into smaller and smaller peices forever, eventually the smallest possible peice would be obtained. He named this peice of matter "Atomos" meaning "not to be cut."
It took at least 2000 years for his idea to be recognized. -
Plato was an Alchemist, however, he did come up with the word element.
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Aristotle and Plato were Alchemists, they taught people that the world was made up of Earth, fire, water, and air.
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Robert Boyle believed that chemical experiments could demonstrate the truth of corpuscularian philosophy.
Corpuscularianism: a form of atomism that was slowly displacing Aristotelian and Paracelsian veiws of the world. -
Laviosier's theory was the Law of Conservation of Mass. This law states that matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant.
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John Dalton deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles. He also beleived that compounds are formed by the joining of two atoms of two or more elements.
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Dmitri Mendeleev discovered the Periodic Law, a law in chemistry, the elements when arranged in the order of their atomic numbers show a periodic variation of the atomic structure and of most of their properties. He also created the periodic table, and predicted the existence and properties of new chemical elements.
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J.J. Thompson provided the first hint that an atom is made of even smaller particles. He proposed a model of an the atom that is sometimes called the "Plum Pudding" model. He concluded that the negative charges came from witn the atom.
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Marie and Pierre Curie studied radioactivity, by doing so, they established that the element thorium was radioactive, and they also discovered two new elements, Polonium and Radium.
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Ernest Rutherford coducted an experiment that involved firing a stream of tiny positively charged particles at a thin peice of gold foil, he concludedd that an atom had a small dense, positively charged center that repelled his posetively charged "bullets."
He called the center of the atom, the "Neucleus." -
Neils Bohr composed the idea that each electron had a specific energy level, and that they all move in definite orbits around the nuecleus.
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Henry G. J. Mosley used self-built equipment to prove that every element's identity is unequally determined by the number of protons it has. He was then able to predict four new chemical elements, which were later found.
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Albert Einstein's had the Theory of Relativity. He determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed of which the observer travels.
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Erwin Shrodinger created the Electron Cloud Model. Using quantum mechanics, chemists can use the electron cloud odel to assign electrons to different atomic orbitals.
