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Download History of Atomic Theory Greek Model Democritus – 2,400 years ago
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History of Atomic Theory Greek Model Democritus – 2,400 years ago Greek philosophers asked the question, Can matter be divided into smaller and smaller pieces forever – or is there a limit? Democritus said eventually the smallest piece would be reached - he named this smallest piece of matter an atom – from Greek word atomos meaning “not to be cut” Dalton’s Model Early 1800s - John Dalton discovered that gases combine as if they were made of individual particles proposed an atomic theory - All elements are composed of atoms. Atoms are indivisible and indestructible particles - Atoms of the same element are exactly alike - Atoms of different elements are different - Compounds are formed by the joining of atoms of two or more elements Daltons atomic theory became on one of the foundations of chemistry Thomson’s Model 1897 J J Thomson provided hint that atoms were made of even smaller particles discovered electrons – negatively charged particles decided if atoms are neutral and there are negative particles than there must be positive particles too designed the “plum pudding” model Rutherford’s Model 1908 – Ernest Rutherford proved Thomson’s model incorrect said the atom had a positively charged center which he called the nucleus said all atom’s positively charged particles were contained in the nucleus – the negatively charged electrons were scattered outside the nucleus meant atoms were mostly empty space – think marble (nucleus) in an baseball stadium Bohr Model 1913 Niels Bohr placed each electron in a specific energy level said electrons move in definite orbits around a nucleus Wave Model Electrons do not move around the nucleus in a definite path Probable location of the electron is based on the energy it has Modern Atomic Model - An atom has a small, positively charged nucleus surrounded by a large region in which there are enough electrons to make the atom neutral. - Important names Werner Heisenberg Erwin Schrodinger
