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CHAPTER 5

CHAPTER 5. The Structure of the Atom. 5.4 Light and Spectroscopy. Today. 460 – 370 BC. 1808. 1897. 1910. 1925. 1870. Democritus Atomism. Crookes Cathode rays. Thomson Discovery of the electron. Rutherford Discovery of the nucleus. Pauli Pauli exclusion principle. Dalton

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CHAPTER 5

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  1. CHAPTER 5 The Structure of the Atom 5.4 Light and Spectroscopy

  2. Today 460 – 370 BC 1808 1897 1910 1925 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Dalton “Modern” atomic theory

  3. Today 460 – 370 BC 1808 1897 1910 1925 1870 Crookes Cathode rays Rutherford Discovery of the nucleus Democritus Atomism Thomson Discovery of the electron Pauli Pauli exclusion principle Dalton “Modern” atomic theory

  4. Today 460 – 370 BC 1808 1897 1910 1925 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Dalton “Modern” atomic theory

  5. Today 460 – 370 BC 1808 1897 1910 1925 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Dalton “Modern” atomic theory Do we have evidence to support these claims?

  6. Light is a form of electromagnetic energy that comes from electrons in atoms The human eye can only detect a certain range of that energy: the visible spectrum.

  7. Light is a form ofelectromagneticenergy that comes from electrons in atoms Thehuman eyecan only detect a certain range of that energy: thevisible spectrum.

  8. Analyzing starlight with a prism (one of the first spectrometers) White light from a lamp or the sun is not truly white!

  9. Visible light is only a small range in the electromagnetic spectrum

  10. We are surrounded by electromagnetic energy

  11. Energy of a photon Remember that light travels as bundles called photons A very small unit of energy 1 electron volt (eV) = 1.602 x 10–19 J.

  12. Calvin the photon (“light particle”)

  13. Wavelength and frequency are related

  14. The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts?

  15. The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked:Frequency and energy Given: Relationships:

  16. The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve:

  17. The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve:

  18. The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve: Answer:Since 1 Hz = 1/s, the frequency is 4.6 x 1014 Hz and the energy is 1.9 eV.

  19. Light from an incandescent light bulb: prism all possible energy levels electron

  20. Light from pure hydrogen: prism fixed energy levels electron

  21. Hydrogen atoms can only absorb and emit light of very specific energies.

  22. Matter and light Why does the atom absorb only specific (discrete) energies?

  23. Matter and light Why does the atom absorb only specific (discrete) energies? Remember: only some energy levels are allowed.

  24. Matter and light Energy levels Energy levels Photon (energy) If: The energy of the photon matches a gap between levels BUT if: The energy of the photon does not match a gap between levels Then: Energy (light) passes through the atom. Then: Energy (light) is absorbed.

  25. Matter and light Energy levels Just after the photon energy is absorbed: another photon is emitted Photon (energy) Energy of the photon matches a gap between levels This new photon can be a specific color (wavelength) Energy (light) is absorbed.

  26. A photon with a wavelength of 414 nm has energy Ephoton = 3.0 eV. Do you expect to see a spectral line with = 414 nm in the emission spectrum of the atom represented by this energy-level diagram? If so, what transition or transitions will emit it?

  27. A photon with a wavelength of 414 nm has energy Ephoton = 3.0 eV. Do you expect to see a spectral line with = 414 nm in the emission spectrum of the atom represented by this energy-level diagram? If so, what transition or transitions will emit it? 3 eV

  28. Each type of atom has a different electron structure. Each element has unique energy levels like afingerprint.

  29. How to read the spectrum cards Spectrum cards

  30. Spectrum cards Combinations of elements contain spectral lines from both.

  31. B. Calcium

  32. Reemission of light has two steps: Energy levels Photon (energy) Photon absorbed Photon emitted Energy of the photon matches a gap between levels

  33. There may be a range of energies, but only specific ones are absorbed Emission spectrum Energy levels Photon (energy) Absorption spectrum

  34. Visible light is only a small range of the electromagnetic spectrum.

  35. Each type of atom has a different electron structure. Each element has unique energy levels like afingerprint.

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