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The History of the Atom Carousel Who-What-When 1. Aristotle and Democritus These contemporary Greek philosophers, c.425BC, had conflicting theories of matter. Aristotle believed in the then current thought that there were four elements: earth, air, fire, and water. To this he added ‘Aether’ meaning outer space and the planets. Democritus believed matter was composed of many tiny pieces and the smallest were indivisible. He called these pieces ‘atomos’ which is Greek for indivisible. 2. Joseph Priestly and Antoine Lavoisier Among Joseph Priestly contributions were the study of ‘airs’ or gasses. In one of his experiments he isolated and ‘discovered’ a new gas – oxygen, in 1772. He visited Antoine Lavoisier in France and explained what he had done. Lavoisier was a noted scientist who used better methodology and measurements in his work. For Priestly’s ‘air’ he ‘invented’ the term oxygen as the emitted gas. Lavoisier published the first text on Chemistry, giving the first names to many of the elements on the periodic table. 3. John Dalton 1802, The Atomic Theory of matter; each type of matter is 1 type of atom – each atom an element is identical – atoms are indivisible and cannot be created or destroyed 4. J. J. Thomson/Ernest Rutherford/James Chadwick Discover’s of the electron (1897), the proton (1909), and the Neutron (1932). 35 years of teacher-student connected study. Rutherford proposed the 1st atomic model; plum pudding/cookie dough 5. Niels Bohr and Gilbert Lewis 1913 - Neils Bohr. Proposes an atomic model where the electrons are arranged in multiple energy layers or electron shells. The shells nearer the nucleus have lower energy and fewer electrons. 1916 - Gilbert Lewis. Proposes the term ‘valence’ for the outer electron shell and determines that atom-atom bonding occurs here.