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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 O3 interact with UV light?
• What is UV light?
http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html
http://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
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
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
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?
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 producedAll could be explained by Quantization – energy can only occur in small discreet units called quanta, i.e., energy is not continuous
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
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 occurQ: 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
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
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
2
1( )n HE R n = 1, 2, 3, 4, ...
n
• 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-
2 2
1 1( )H
i f
E R
h h n n