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THE ATOM

THE ATOM. Modern Atomic Theory vs. Old Atomic Theory. Democritus. Greek philosopher who lived between 470-380 B.C. Developed the concept of the 'atom', Greek for 'indivisible'. Believed that everything in the universe was made up of atoms, which were

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THE ATOM

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  1. THE ATOM

  2. Modern Atomic Theory vs. Old Atomic Theory HFinks '07

  3. Democritus • Greek philosopher who lived between 470-380 B.C. • Developed the concept of the 'atom', Greek for 'indivisible'. • Believed that everything in the universe was made up of atoms, which were microscopic and indestructible. HFinks '07

  4. Fundamental Chemical Laws HFinks '07

  5. Law of Conservation of Mass • Antoine Lavoisier • Mass is neither created nor destroyed during chemical or physical reactions. • Total mass of reactants = Total mass of products HFinks '07

  6. John Dalton’s Atomic Theory (1808) Dalton’s Theory states: • All matter is composed of tiny particles called atoms. HFinks '07

  7. Dalton’s Theory states: • Atoms cannot be • sub-divided • created • or destroyed HFinks '07

  8. Modern Atomic Theory states: • Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions! HFinks '07

  9. Dalton’s Theory states: • In chemical reactions, atoms are • combined • separated • or rearranged The atoms themselves are not changed HFinks '07

  10. Dalton’s Theory states: • Atoms of a given element are • identical in size • mass • and other properties. HFinks '07

  11. Dalton’s Theory states: • Atoms of different elements • differ in size • mass • and other properties combine in simple whole-number ratios to form chemical compounds. HFinks '07

  12. Modern Atomic Theory states: • Atoms of an element have a characteristic average mass which is unique to that element. HFinks '07

  13. The Law of Definite Proportion A given compound always contains exactly the same proportions of elements by mass. HFinks '07

  14. Example: Definite Proportions • Two compounds containing carbon and oxygen • CO = carbon monoxide • The ratio of carbon to oxygen will always be 1:1 • CO2 = carbon dioxide • The ratio of carbon to oxygen will always be 1:2 HFinks '07

  15. Law of Multiple Proportions • John Dalton • When two elements form a series of compounds, the ratio of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. HFinks '07

  16. Example: Multiple Proportions • Ratios of nitrogen oxygen A = 1.750 = 2 B 0.875 1 B = 0.875 = 2 C 0.4375 1 A = 1.750 = 4 C 0.4375 1 HFinks '07

  17. What does this mean? • Compound A contains twice as much nitrogen per gram of oxygen as does compound B and • Compound B contains twice as much nitrogen per gram of oxygen as does compound C HFinks '07

  18. Early Experiments What is an atom made of? How do the atoms of the various elements differ? HFinks '07

  19. J. J. ThomsonCharge-to-Mass ratio of an Electron HFinks '07

  20. J.J. Thomson Thomson found that when high voltage was applied to a cathode-ray tube, a “ray” he called a cathode ray was produced. Thomson postulated that the ray was a stream of negatively charged particles, now called electrons. Thomson determined the charge-to-mass ratio of an electron. e/m = 1.76 x 108 C/g HFinks '07

  21. Cathode-Ray Tube • The fast-moving electrons excite the gas in the tube, causing a glow between the electrodes. The green color is due to the response of the screen (coated with zinc sulfide) to the electron beam. HFinks '07

  22. Some Modern Day Cathode Tubes Computer Screen Television Screen HFinks '07

  23. Plum Pudding Model of Atom It is called the plum pudding model because the electrons are like raisins deposited in a pudding (the positive charge cloud? HFinks '07

  24. Ernest RutherfordNucleus & Proton Postulated the nuclear atom. Invented the name proton for the nucleus of the hydrogen atom HFinks '07

  25. Rutherford’s Experiment • Flash animations from Essential Chemistry by Raymond Chang http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf HFinks '07

  26. Rutherford’s Experiment HFinks '07

  27. Rutherford directed alpha particles at a thin sheet of metal foil. Most of the alpha particles passed straight through. Some were deflected Some were reflected, never hitting the detector. HFinks '07

  28. Conclusion • Most of the alpha particles passed through the foil because the atom is mostly open space. • Deflected alpha particles are those that had a close encounter with the massive positive center of the atom • Reflected alpha particles are those that made a direct hit on the massive positive center • Most of the atom is empty space. HFinks '07

  29. Robert MillikanCharge on the Electron HFinks '07

  30. Millikan’s Experiment • This apparatus was used by Millikan to determine the charge on the electron. • The voltage was adjusted across the plates to halt the fall of charged oil droplets. HFinks '07

  31. Millikan’s experiment showed that the charge on an oil drop is always a whole-number multiple of the electron charge. HFinks '07

  32. With this value and the charge-to-mass ratio determined by Thomson, Millikan calculated the mass of an electron as 9.11 x 10-31 kg. HFinks '07

  33. James Chadwick • Credited with discovering the neutron. • The neutron is neutral and is found in the nucleus of the atom. HFinks '07

  34. Mass and Charge of Electron, Proton and Neutron HFinks '07

  35. The Periodic Table Introduction HFinks '07

  36. Squares on Table • Each small square of the periodic table shows the Name Symbol Atomic Number Atomic mass units/molar mass/atomic weight HFinks '07

  37. Letters in the boxes are the symbols for the elements. • One letter: capitalized • Two letter: 1st letter is capitalized 2nd letter is lowercase. Examples: Hydrogen – H Calcium - Ca HFinks '07

  38. Numbers shown in each box whole number = atomic number • Number with values to the right of the decimal point = atomic mass unit Carbon 6 C 12.0107 HFinks '07

  39. Older Names vs. Modern Names • Stibium –antimony • Cuprum – copper • Aurum – gold • Ferrum – iron • Plumbum – lead • Hydrargyrum – mercury • Kalium – potassium • Natrium – sodium • Stannum – tin • Wolfram - tungsten HFinks '07

  40. Vertical Columns • groups or families. Each column contains elements with similar chemical properties HFinks '07

  41. Horizontal Rows • Periods or Series HFinks '07

  42. Vertical Column Groups • IA – Alkali meals • IIA – Alkaline earth metals • VIIA – Halogens • VIIIA – Noble or inert gases HFinks '07

  43. Brainaic: Alkali Metals • C:\Documents and Settings\F:\Chemistry\bae90a9ed1e71a9a.avi.mp4 HFinks '07

  44. Group and Period Numbers HFinks '07

  45. Group and Period Numbers HFinks '07

  46. Two Main Sections of Table • Metals • Nonmetals HFinks '07

  47. Metals are located to the left of the metalloids (red boxes). Nonmetals are located to the right of the metalloids. (blue boxes). HFinks '07

  48. Two Rows at Bottom • Lanthanide Series • Actinide Series HFinks '07

  49. Two elements that are liquid (blue) at room temperature: • Mercury (Hg) • Bromine (Br) The “red symbols” represent the gases. The “black symbols” represent the solids HFinks '07

  50. Characteristic of Metals • Good conductors of electricity and heat • High luster • Ductile • Malleable HFinks '07

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