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Theory: Everything is made up of individual particles (atoms) and they cannot be created, destroyed, or divided. Link: http://www.universetoday.com/60058/democritus-atom/
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John Dalton built his theory off of Democritus by restating that all matter is made up of atoms and tiny paricals that are indestructable and cannot be divided. He added that all atoms of the same element are exactly alike while the atoms of an element are different from those of another element. Also, he discovered that atoms combine in simple whole-number ratios, and atoms are separated, combined, or rearranged in a chemical reaction. Link: http://www.biography.com/people/john-dalton-9265201
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JJ Thomson used a cathode ray tube with a negative charge to discover elements. He then realized that the accepted model of an atom did not account for the negatively or positively charged particles. Thomson's theory is called plum pudding because he noticed that like plums in the pudding, the electrons are dispersed throughout the atom. Link: http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/thomson.aspx
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Rutherford used gold foil in order to discover the nucleus. He concluded that the atom consists of a dense positively charged nucleus in the center of the atom surrounded by negatively charged particles. He said that the atom consists mostly of space. Link: http://www.rsc.org/chemsoc/timeline/pages/1911.html
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Using the bright light spectrum, Bohr discovered that electrons orbit the nucleus of an atom. As they change their orbit, they either absorb or release energy. Link:http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-facts.html
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In 1926, Schrödinger stated that the electrons in the atoms of the element hydrogen move in a wave motion. He created a formula that described the liklihood of finding an electron in a certain position.When the electron cloud is most dense , the propability of finding an electron is greater and vice-versa. Link: http://www.nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-bio.html
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James Chadwick discovered that the composition of atoms also contained neutrons which are located in the center of atoms and weigh the same as protons. Link: http://jameschadwickatomictheory.weebly.com/
