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Democritus

Democritus. 440 BC. His idea: If you keep cutting matter in half, eventually you get a particle that you can’t cut anymore. He called this particle “ atomos ” which means “not able to be divided”. Aristotle. NO!. 300’s BC. Disagreed with Democritus: Matter can be cut infinitely

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Democritus

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  1. Democritus 440 BC His idea: If you keep cutting matter in half, eventually you get a particle that you can’t cut anymore. He called this particle “atomos” which means “not able to be divided”

  2. Aristotle NO! 300’s BC • Disagreed with Democritus: • Matter can be cut infinitely • There’s no such things as “atoms”! Aristotle was more influential, so people believed him over Democritus. UNTIL …….

  3. John Dalton Atomic theory! 1766 - 1844 Developed his “Atomic Theory” based on experiments done by him and other scientists during previous 200 years or so. His book called “A new System of Chemical Philosophy” had 900 pages… …but just 5 pages in the book made him famous!

  4. An excerpt from Dalton’s book A New System of Chemical Philosophy

  5. Dalton’s Atomic Theory: All matter is made of atoms, which can’t be created, divided, or destroyed. Atoms of the same element are identical, atoms of different elements are different. Atoms join with other atoms to make new substances. HEY!! But not ALL of Dalton’s ideas were completely correct…

  6. J.J. Thomson Performed experiments using a cathode ray tube. Late 1800’s Cathode ray tube experiment

  7. Thomson had discovered ELECTRONS! I think an atom looks like plum pudding: negatively charged electrons scattered throughout a positively charged substance!

  8. Ernest Rutherford 1871 - 1937 • A student of Thomson. • He decided to test Thomson’s “Plum Pudding” theory of the atom.

  9. Rutherford's experiment

  10. Rutherford was shocked by the results! It was quite the most incredible event that has ever happened to me in my life! It was almost as if you fired a 15-inch shell into a piece of tissue paper and it came back and hit you.

  11. Rutherford’s new model of the atom: • Small positively charged nucleus • Electrons orbiting very far away • He realized most of the atom is empty space!

  12. Niels Bohr • Studied the way light interacted with atoms. • Concluded that electrons can only orbit in fixed pathsor energy levels. 1885-1962 Energy levels!

  13. Review Atoms! Democritus Aristotle No Atoms! Analyzed experiments, Developed 3-part Atomic Theory. Dalton Cathode ray tube experiment, Discovered electrons, Made “plum pudding” model of atom. Thomson Gold foil experiment, Discovered nucleus, Revised atom model. Rutherford Bohr Discovered electron energy levels.

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