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http://en.wikipedia.org/wiki/Conservation_of_mass Antoine Lavoisier lays foundations for the Law of Conservation of Mass by observing that matter can go through a chemical change of state, but still have the same mass.
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http://dl.clackamas.edu/ch104-04/dalton's.htm John Dalton states that all matter is composed of indivisable atoms.
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http://en.wikipedia.org/wiki/Dmitri_Mendeleev#Periodic_table_2 Dmitri Mendeleev publishes periodic table of all known elements (at the time 56). The data was initially compiled for his textbook, "Principals of Chemistry", and he began to see patterns in the elements which encouraged him to continue his studies.
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http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html In 1897, after experiments dealing with the study of cathode rays, J.J Thompson announces the existance of the electron. He also suggested that electrons are distributed evenly throughout the atom.
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http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html Ernest Rutherford concluded that the atom is made up of mostly empty space after studying the scattering of alpha rays inside the atom. He also suggests the idea of the nucleus, or inner core of the atom having a positive charge.
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http://en.wikipedia.org/wiki/Bohr_model Neils Bohr introduces a depiction of the atom's electrons in orbit around the nucleus attracted by electrostatic forces, through quantum-mechanics.
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http://en.wikipedia.org/wiki/Werner_Heisenberg Werner Heisenberg publishes the first work in the famous trilogy know as the matrix mechanics formulation of quantum mechanics. Quantum Chemistry comes from the application of QM (Quantum Mechanics) to chemistry aiding in determining energy levels of molecules.
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http://en.wikipedia.org/wiki/James_Chadwick James Chadwick discovers the existance of the neutron in the atomic neucleus having .1 more mass than the proton.
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http://en.wikipedia.org/wiki/J._Robert_Oppenheimer#Manhattan_Project Robert Oppenheimer and various other renoun scientists make huge leaps for chemistry in the feild of nuclear fission to create and explode the worlds first atomic bomb.
