Atoms Timeline Essay

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Aristotle: How the model contradicted any previous models? - He argued against the theories of Greek philosopher Leucippus of Miletus and his student Democritus of Abdera in the 5th century B.C Contribution? - He believed that a piece of matter could be divided up an infinite number of times. He suggested that everything in this world was made up of some combination of four elements: earth, fire, water, and air. The elements were acted upon by the two forces of gravity and levity. His theory held two forces conflict and harmony. Aristotle’s theory was used for almost 2000 years, until after the scientific revolution. The year/century the model was adopted? - 384 – 322 B.C. Henri Becquerel: How the model contradicted any previous models? - He forced scientists to change their ideas about atomic structure. Contribution? - His discovery of radioactivity in uranium forced scientists to change their ideas about atomic structure. Radioactivity demonstrated that the atom was neither indivisible nor immutable. The year/century the model was adopted? - 1896 Niels Bohr: How the model contradicted any previous models? - Bohr made improvements to Ernest Rutherford’s model with the implementation of Max Planck’s new idea of quanta. Contribution? - He proposed that electrons existed at set levels of energy at fixed distances from the nucleus. If the atom absorbed energy, the electron jumped to a level further from the nucleus: if it lost energy it fell to a level closer to the nucleus. They year/century the model was adopted? - 1913 James Chadwick: Contribution? - Chadwick proved the existence of neutrons. For his discovery, he was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935. The year/century the model was adopted? - 1931 Marie & Pierre Curie: Contribution? - Pierre

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