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wavelength

wavelength. Visible light. Amplitude. wavelength. Node. Ultraviolet radiation. Chapter 6: Electromagnetic Radiation. Figure 7.1. Short wavelength --> high frequency high energy. Long wavelength --> small frequency low energy. Which has the longest wavelength?. Infrared

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wavelength

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  1. wavelength Visible light Amplitude wavelength Node Ultraviolet radiation Chapter 6: Electromagnetic Radiation

  2. Figure 7.1

  3. Short wavelength --> high frequency high energy Long wavelength --> small frequency low energy

  4. Which has the longest wavelength? • Infrared • Ultraviolet • X-rays • Radio waves

  5. Rank the following in order of increasing frequency: microwaves radiowaves X-rays blue light red light UV light IR light

  6. Waves have a frequency • Use the Greek letter “nu”, , for frequency, and units are “cycles per sec” • All radiation:  •  = c • c = velocity of light = 3.00 x 108 m/sec • Long wavelength --> small frequency • Short wavelength --> high frequency

  7. What is the wavelength of WONY? What is the wavelength of cell phone radiation? Frequency = 850 MHz What is the wavelength of a microwave oven? Frequency = 2.45 GHz

  8. Quantization of Energy Light acts as if it consists of particles called PHOTONS,with discrete energy. Energy of radiation is proportional to frequency E = h •  h = Planck’s constant = 6.6262 x 10-34 J•s

  9. E = h •  Relationships:

  10. Short wavelength light has: • High frequency and low energy • High frequency and high energy • Low frequency and low energy • Low frequency and high energy

  11. Rank the following in order of increasing photon energy: microwaves radiowaves X-rays blue light red light UV light IR light

  12. E = h • n What is the energy of a WONY photon?

  13. Energy of Radiation What is the frequency of UV light with a wavelength of 230 nm? What is the energy of 1 photon of UV light with wavelength = 230 nm?

  14. What is the energy of a photon of 525 nm light? • 3.79 x 10-19 J • 4.83 x 10-22 J • 3.67 x 1020 J • 8.43 x 1023 J

  15. What is the energy of a mole of 230 nm photons? Can this light break C-C bonds with an energy of 346 kJ/mol?

  16. Does 1200 nm light have enough energy to break C-C bonds?

  17. Where does light come from? • Excited solids emit a continuous spectrum of light • Excited gas-phase atoms emit only specific wavelengths of light (“lines”)

  18. Light emitted by solids

  19. Light emitted by hydrogen gas

  20. The Bohr Model of Hydrogen Atom • Light absorbed or emitted is from electrons moving between energy levels • Only certain energies are observed • Therefore, only certain energy levels exist • This is the Quanitization of energy levels

  21. Emission spectra of gaseous atoms • Excited atoms emit light of only certain wavelengths • The wavelengths of emitted light depend on the element.

  22. Line spectra of atoms

  23. Energy Absorption and Emissionsim

  24. For H, the energy levels correspond to: Energy level diagram:

  25. Each line corresponds to a transition: Example: n=3  n = 2

  26. Explanation of line spectra Balmer series

  27. Longest wavelength emission? • 1 • 2 • 3 • 4 • 5

  28. Longest wavelength absorption? • 1 • 2 • 3 • 4 • 5

  29. Lowest energy emission? • 1 • 2 • 3 • 4 • 5

  30. Lowest energy absorption? • 1 • 2 • 3 • 4 • 5

  31. Ionization? • 1 • 2 • 3 • 4 • 5

  32. Matter Waves • All matter acts as particles and as waves. • Macroscopic objects have tiny waves- not observed. • For electrons in atoms, wave properties are important. • deBroglie Equation:

  33. Can see matter waves in experiments

  34. Matter waves Macroscopic object: 200 g rock travelling at 20 m/s has a wavelength: Electron inside an atom, moving at 40% of the speed of light:

  35. Heisenberg Uncertainty Principle • Can’t know both the exact location and energy of a particle • So, for electrons, we DO know the energy well, so we don’t know the location well

  36. Schrodinger’s Model of H • Electrons act as standing waves • Certain wave functions are “allowed” • Wave behavior is described by wave functions:  • 2describes the probability of finding the electron in a certain spot • Also described as electron density

  37. Hydrogen Wave Functions

  38. Example Wavefunction Equation slightly simplified:

  39. Where is this function zero or near zero? • When x = 0 • When r = 0 • When r is large

  40. It’s all about orbitals • Each wavefunction describes a shape the electron can take, called an ORBITAL • Allowed orbitals are organized by shells and subshells • Shells define size and energy (n = 1, 2, 3, …) • Subshells define shape (s, p, d, f, …) • Number of orbitals is different for each subshell: s = 1 orbital p = 3 orbitals d = 5 orbitals f = 7 orbitals

  41. NODES Spherical Nodes

  42. Quantum Numbers and Numbers of Orbitals

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