Bohr Model And Aes


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Bohr Model And Aes

  1. 1. How does this work? (Neon Signs)
  2. 2. What do we know about neon signs? <ul><li>Electricity is passed through tube full of neon gas </li></ul><ul><li>Neon atoms in tube absorb this energy </li></ul><ul><ul><li>What happens when something absorbs energy? </li></ul></ul><ul><li>Neon atoms in tube become excited </li></ul><ul><ul><li>Stable of Unstable? </li></ul></ul><ul><ul><li>What happens when something is unstable? </li></ul></ul><ul><ul><li>What do we see released energy as? </li></ul></ul><ul><ul><ul><li>Electromagnetic radiation…visible light!!! </li></ul></ul></ul>
  3. 3. EM spectrum <ul><li>What happens when we pass sunlight through a prism? </li></ul><ul><ul><li>Continuous spectrum of colors </li></ul></ul><ul><ul><li>ROYGBIV </li></ul></ul>
  4. 4. What happens when we pass light from neon gas or hydrogen gas through prism? <ul><li>Separation of colors </li></ul><ul><li>Discontinuous spectrum </li></ul><ul><li>This is called… </li></ul>
  5. 5. ATOMIC EMISSION SPECTRUM (AES) <ul><li>AES of an element is the set of frequencies of the electromagnetic radiation emitted by the atoms of that element </li></ul><ul><li>Individual lines of color </li></ul><ul><li>Only certain lines of color appear for certain elements… </li></ul><ul><ul><li>What does this mean…???? </li></ul></ul><ul><li>Every element has a unique AES </li></ul><ul><li>Why is this important? </li></ul>
  6. 8. Hydrogen Atom <ul><li>Why did scientists want to use hydrogen? </li></ul><ul><ul><li>How many protons? </li></ul></ul><ul><ul><li>How many electrons? </li></ul></ul><ul><ul><li>Do you think it is easy to use? </li></ul></ul><ul><ul><li>Check out the AES of hydrogen gas… </li></ul></ul>
  7. 10. Neils Bohr (1913) <ul><li>Danish Physicist </li></ul><ul><li>Worked with Rutherford </li></ul><ul><li>Quantum Model of Hydrogen atom </li></ul><ul><ul><li>Predicted lines of Hydrogen AES </li></ul></ul>
  8. 11. <ul><li>Hydrogen has only one electron but why do we get different colored lines on AES??? </li></ul><ul><ul><li>We get hydrogen atoms excited… </li></ul></ul><ul><ul><li>Electrons move to excited levels </li></ul></ul><ul><li>H has certain allowable energy states…. </li></ul><ul><ul><li>The lowest energy state is called the GROUND STATE </li></ul></ul>
  9. 12. Bohr’s Hydrogen Orbits… <ul><li>He related H’s energy states to the motion of an electron in an atom </li></ul><ul><li>Single electron in moves around nucleus in circular orbits </li></ul><ul><li>Smaller orbit, smaller radius, closer to nucleus means…? </li></ul><ul><ul><li>Lower energy level </li></ul></ul><ul><li>Larger orbit, larger radius, farther from the nucleus means…? </li></ul><ul><ul><li>Higher energy level </li></ul></ul>
  10. 14. Bohr’s Quantum Model <ul><li>Assigned quantum numbers, n, to each orbit </li></ul><ul><li>Calculated orbits radius </li></ul><ul><ul><li>Chart on page 127 </li></ul></ul><ul><li>1 st orbit  n=1 (first energy level) </li></ul><ul><li>2 nd orbit  n=2 (second energy level) </li></ul><ul><li>3 rd orbit  n=3 (third energy level) </li></ul>
  11. 17. When we add energy, what happens to electron? <ul><li>Electron excited </li></ul><ul><li>Moves to next energy level </li></ul><ul><li>Excited=? </li></ul><ul><ul><li>unstable </li></ul></ul><ul><li>What happens when something is unstable? </li></ul><ul><ul><li>Wants to get back to being stable </li></ul></ul><ul><ul><li>Releases energy </li></ul></ul><ul><ul><li>Goes back down to lower energy level </li></ul></ul><ul><li>Photon is emitted corresponding to the 2 different energy levels associated with the 2 orbits </li></ul>
  12. 19. NEW EQUATION <ul><li>/_ E= E higher e- orbit - E lower e- orbit =E photon =hv </li></ul><ul><li>Only certain energies are possible so only certain frequencies, v, of EM radiation are emitted </li></ul><ul><li>Lets look at the AES of Hydrogen… </li></ul>
  13. 20. <ul><li>How many lines are there? </li></ul><ul><li>So how many different types of radiations are we seeing? </li></ul><ul><li>There are 4 electron transitions account for lines in the hydrogen spectrum </li></ul><ul><li>Going from 3 rd orbital to 2 nd orbital… </li></ul><ul><li>Going from 4 th orbital to 2 nd orbital… </li></ul><ul><li>Going from 5 th orbital to 2 nd orbital… </li></ul><ul><li>Going from 6 th orbital to 2 nd orbital… </li></ul>
  14. 21. Names for these lines… <ul><li>Balmer Series </li></ul><ul><ul><li>The 4 visible color lines </li></ul></ul><ul><ul><li>Electrons that drop into n=2 </li></ul></ul><ul><li>Other electrons transitions not visible </li></ul><ul><ul><li>Lyman series </li></ul></ul><ul><ul><ul><li>Ultraviolet light </li></ul></ul></ul><ul><ul><ul><li>Electrons drop into n=1 </li></ul></ul></ul><ul><ul><li>Paschen series </li></ul></ul><ul><ul><ul><li>Infrared </li></ul></ul></ul><ul><ul><ul><li>Electrons drop into n=3 </li></ul></ul></ul>
  15. 23. Problems with Bohr’s Model <ul><li>Predicted AES lines of H but not any other elements </li></ul><ul><li>Did not account for all chemical behavior </li></ul><ul><li>Big problem… </li></ul><ul><ul><li>Electrons don’t move in circular orbits </li></ul></ul><ul><ul><li>Time for a new model… </li></ul></ul>