CHM 113 Chemistry and the Environment

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/EMSp
ec2.html
3
http//astrosun.tn.cornell.edu/courses/astro201/em
spectrum.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/?
• Plancks constant, h 6.63 x 10-34 J.s
• QCompare 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 doesnt 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.
  OO 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 (cant 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
  (n3 to n2)
• A 657 nm (actual 656 nm)
• Model doesnt work for species other than 1 e-