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Chapter 4

Chapter 4. Atoms and their structure. History of the atom. Not the history of atom, but the idea of the atom Original idea Ancient Greece (400 B.C..) Democritus - Greek philosopher First to state that matter is made of separate, discrete particles. Another Greek.

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Chapter 4

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  1. Chapter 4 Atoms and their structure

  2. History of the atom • Not the history of atom, but the idea of the atom • Original idea Ancient Greece (400 B.C..) • Democritus - Greek philosopher • First to state that matter is made of separate, discrete particles

  3. Another Greek • Aristotle - Famous philosopher • All substances are made of 4 elements • Fire - Hot • Air - Light • Earth - Cool, heavy • Water - Wet • Blend these in different proportions to get all substances

  4. Who’s Next? • Late 1700’s - John Dalton- England • English Teacher- summarized results of his experiments and those of other’s • In Dalton’s Atomic Theory • Atoms of different element form compounds; Law of Definite Composition

  5. Law of Definite Proportions • Each compound has a specific ratio of elements • It is a ratio by mass • Water is always 8 grams of oxygen for each gram of hydrogen or 2 atoms of hydrogen with 1 atom of oxygen.

  6. J.J. Thomson Created a vacuum in a tube Light came from cathode end Cathode rays affected by magnets and electricity but not gravity. Discovered cathode rays were negatively charged. Every element emitted these rays…..electrons

  7. Voltage source Thomson’s Experiment - + Vacuum tube Metal Disks

  8. Voltage source Thomson’s Experiment - +

  9. Voltage source Thomson’s Experiment - +

  10. Voltage source Thomson’s Experiment - +

  11. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

  12. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

  13. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

  14. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

  15. Voltage source Thomson’s Experiment • By adding an electric field

  16. Voltage source Thomson’s Experiment + - • By adding an electric field

  17. Voltage source Thomson’s Experiment + - • By adding an electric field

  18. Voltage source Thomson’s Experiment + - • By adding an electric field

  19. Voltage source Thomson’s Experiment + - • By adding an electric field

  20. Voltage source Thomson’s Experiment + - • By adding an electric field

  21. Voltage source Thomson’s Experiment + - • By adding an electric field he found that the moving pieces were negative

  22. Welhelm Roentgen • Discovered x-rays in 1896

  23. Rutherford’s experiment Ernest Rutherford English physicist. (1910) Used radioactivity Alpha particles - positively charged pieces given off by uranium Shot them at gold foil which can be made a few atoms thick Discovered the middle of an atom is extremely dense Nucleus

  24. Florescent Screen Lead block Uranium Gold Foil

  25. What he expected

  26. Because

  27. Because, he thought the mass was evenly distributed in the atom

  28. Because, he thought the mass was evenly distributed in the atom

  29. What he got

  30. + How he explained it • Atom is mostly empty • Small dense, positive piece at center • Alpha particles are deflected by it if they get close enough

  31. +

  32. Niels Bohr • Quantum Model • Two regions • Nucleus- protons and neutrons; + • Electron cloud- region where you might find an electron; -

  33. Louise de Broglie French physicist Proposed that all matter acts like waves Developed the deBroglie’s hypothesis.

  34. Werner Heisenberg German physicist You can never know the speed and position of an electron at the same time. Developed the Heisenberg Uncertainty Principle.

  35. Dalton’s Atomic Theory All matter is made of tiny indivisible particles called atoms. Atoms of the same element are identical, those of different atoms are different. Atoms of different elements combine in whole number ratios to form compounds Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

  36. Law of Multiple Proportions • If two elements form more than one compound, the ratios will always be a whole number. • CO or CO2 • H2O or H2O2

  37. Parts of Atoms • J. J. Thomson - English physicist. 1897 • Made a piece of equipment called a cathode ray tube. • It is a vacuum tube - all the air has been pumped out.

  38. Thomsom’s Model • Found the electron • Couldn’t find positive (for a while) • Said the atom was like plum pudding • A bunch of positive stuff, with the electrons able to be removed

  39. What’s in the Nucleus • One Problem – the atom’s had more mass than could be attributed to the protons • Sir James Chadwick – identified the neutron in 1932 • Neutral particle • Approximately same size as proton

  40. Density and the Atom • Since most of the particles went through, it was mostly empty. • Because the pieces turned so much, the positive pieces were heavy. • Small volume, big mass, big density • This small dense positive area is the nucleus

  41. Size of an atom • Atoms are small. • Measured in picometers, 10-12 meters • Hydrogen atom, 32 pm radius • Nucleus tiny compared to atom • IF the atom was the size of a stadium, the nucleus would be the size of a marble. • Radius of the nucleus near 10-15m. • Density near 1014 g/cm

  42. Subatomic particles Actual mass (g) Relative mass Name Symbol Charge Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron n0 0 1 1.67 x 10-24

  43. Counting the Pieces • Atomic Number = number of protons • # of protons determines kind of atom • the same as the number of electrons in the neutral atom • Mass Number = the number of protons + neutrons

  44. Isotopes • Dalton was wrong. • Atoms of the same element can have different numbers of neutrons • Isotopes have same number of protons but different numbers of neutrons • Same element different mass number

  45. Isotopic Notation • Contain the symbol of the element, the mass number and the atomic number Mass number X Atomic number

  46. Isotopic Notation • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 19 F 9

  47. Isotopic Notation • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 80 Br 35

  48. Isotopic Notation • if an element has an atomic number of 34 and a mass number of 78 what is the • number of protons • number of neutrons • number of electrons • Complete symbol

  49. Isotopic Notation • if an element has 91 protons and 140 neutrons what is the • Atomic number • Mass number • number of electrons • Complete symbol

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