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Chapter 2 (CIC) and Chapter 6 (CTCS)

Chapter 2 (CIC) and Chapter 6 (CTCS). Read in CTCS Chapter 6.1-3 Problems in CTCS: 1, 3, 5, 7, 9, 13, 15, 19, 23, 25, 27, 29. Light. How does O 3 interact with UV light? What is UV light?. http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html.

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Chapter 2 (CIC) and Chapter 6 (CTCS)

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  1. Chapter 2 (CIC) and Chapter 6 (CTCS) • Read in CTCS Chapter 6.1-3 • Problems in CTCS: 1, 3, 5, 7, 9, 13, 15, 19, 23, 25, 27, 29

  2. Light • How does O3 interact with UV light? • What is UV light? http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

  3. http://astrosun.tn.cornell.edu/courses/astro201/emspectrum.htmhttp://astrosun.tn.cornell.edu/courses/astro201/emspectrum.htm • Prism breaks visible light into separated colors • Light is a wave • Visible light has wavelengths () from 400 – 700 nm (VIBGYOR) • Radio waves ~ football field • X-rays ~ atom

  4. Waves of Light • Wavelength is distance between successive peaks and has units of m • Frequency is the number of waves passing a fixed point in one second () and has units of Hz or 1/s •  = c/  where c is the speed of light (3.00 x 108 m/s Q: Calculate the frequency of red light A: 7.5 x 1014 s-1

  5. Q: If the radio in front of you is off, are you being hit by radio waves? Q: Arrange Visible, UV, and IR light from shortest to longest wavelength Q: Arrange Visible, UV, and IR light from shortest to longest frequency

  6. What does the sun emit? *Stanitski, D.L.; Eubanks, L.P.; Middlecamp, C.H.; Stratton, W.J. Chemistry in Context: Applying Chemistry to Society, 3rd Edition, McGraw-Hill, Boston, MA, 2000, pg 58. Why is UV light most harmful when it consists of only 8% of the light coming from the sun?

  7. Dual Nature of Light • None of the following could be explained by classical physics • All solids emit electromagnetic radiation • Usually infrared (night vision goggles) • Black-body radiation Any object when heated releases light (750º-red, 1200º-white) • Photoelectric Effect - when a beam of light shines on metal, a beam of electrons is produced • All could be explained by Quantization – energy can only occur in small discreet units called quanta, i.e., energy is not continuous

  8. Quantum Energy • Radiation considered as consisting of small discreet bundles of energy called photons • Energy is particle like without the mass • E = h = hc/ • Planck’s constant, h = 6.63 x 10-34 J.s Q:Compare the energies of a radiowave (100 MHz FM) vs. UV light (300 nm) A: 6.63 x 10-26 J/photon vs. 6.63 x 10-19 J/photon

  9. UV Light • UV light has more energy than visible or IR light • 7 x 10-19 J are required to increase the content of melanin causing tanning to occur Q: Can all the radio particles be added or stored to add up to 7 x 10-19 J? A: A photon either has or doesn’t have the energy to make this happen • With 400 nm light and chlorophyll, CO2 +H2O  C6H12O6 • UV has enough E to eject e- and in some cases break bonds which can cause cancer

  10. Q: An O-O bond requires 2.4 x 10-19 J to break. O=O is 8.2 x 10-19 J. What wavelength of light would this require? A: 830 nm compared to 240 nm

  11. More Evidence of Quanta • Line Spectra • http://home.achilles.net/~jtalbot/data/elements/ • Niels Bohr developed the Planetary Model for an atom (can’t be) • Electrons can jump from one orbit to the next (quantum leaps only) • En is the energy of the electron in the nth orbit • RH is the Rydberg constant (2.18 x 10-18 J) • n is the orbit that the electron is in

  12. When an electron gains enough energy to escape an orbit and then relaxes, it must give off energy Q: Calculate the wavelength of the red line in H (n=3 to n=2) A: 657 nm (actual = 656 nm) • Model doesn’t work for species other than 1 e-

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