1. 1 Ch 2- Ozone Layer http://jwocky.gsfc.nasa.gov/teacher/ozone_overhead.html ( NASA)http://jwocky.gsfc.nasa.gov/teacher/ozone_overhead.html NASA http://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/uv_c urrent.html ( The UV Index Forecast)http://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/uv_c urrent.html The UV Index Forecast http://toms.gsfc.nasa.gov/multi/monoct.gif ( global images)http://toms.gsfc.nasa.gov/multi/monoct.gif global images http://toms.gsfc.nasa.gov/multi/min_ozone.jpg ( minimum ozone levels)http://toms.gsfc.nasa.gov/multi/min_ozone.jpg minimum ozone levels http://jwocky.gsfc.nasa.gov/teacher/ozone_overhead_archive.html (archive of satellite data)http://jwocky.gsfc.nasa.gov/teacher/ozone_overhead_archive.htmlarchive of satellite data http://www.cpc.noaa.gov/products/stratosphere/winter_bulletins/ (NOAA Climate Prediction Center)http://www.cpc.noaa.gov/products/stratosphere/winter_bulletins/NOAA Climate Prediction Center

2. Chapter 2: Protecting the Ozone Layer Isn’t ozone hazardous to human health? What can we do (if anything) to help stop the depletion of our ozone layer? Why do we need to do to protect the ozone layer? Why is the ozone layer getting smaller?

3. Ozone Formation Energy + 3 O 2 2 O 3 Ozone is an allotropic form of oxygen. Energy must be absorbed (endothermic) for this reaction to occur. ElementAllotropes oxygenO 2, O 3 carbongraphite, diamond, buckminister fullerenes 2.1 An allotrope is two or more forms of the same element that differ in their chemical structure and therefore their properties.

4. Structure of the Atom Year of DiscoveryDiscovered by Proton 1911Rutherford Neutron 1932Chadwick Electron 1897Thomson

5. O 8 16.00 Atomic number (Z) Mass number (A) -The number of protons. (nuclear charge) -The sum of the protons and neutrons. 2.2

6. The electrons in the outermost energy levels are called valence electrons. 2.2 The group number (of the representative elements) on the periodic table tells you the number of valence electrons. 1A 2A 3A 4A5A 6A7A 8A Group 1A: 1 valence electron Group 3A: 3 valence electrons

7. 2.2 Isotopes are two or more forms of the same element (same number of protons) whose atoms differ in number of neutrons, and hence in mass. Isotopes of carbon: C-12, C-13, C-14 also written as: 12 C 13 C 14 C

9. Representing molecules with Lewis structures : 2.3 Consider water, H 2 O: 1. Find sum of valence electrons: 1 O atom x 6 valence electrons per atom = 6 +2 H atoms x 1 valence electron per atom = +2 8 valence electrons 2. Arrange the electrons in pairs; use whatever electron pairs needed to connect the atoms, then distribute the remaining electron pairs so that the octet rule is satisfied:

10. 2.3 Representing molecules with Lewis structures: Typical valence for selected atoms = the # of bonds an atom typically forms ElementTypical valence Classification H, X (X= F, Cl, Br, I) 1monovalent O2divalent N3trivalent C4tetravalent

11. 2.3 Representing molecules with Lewis structures: Multiple bonds Triple bondDouble bond Occasionally a single Lewis structure does not adequately represent the true structure of a molecule, so we use resonance forms:

12. 2.3 Try these; draw valid Lewis structures for: HNO 3 CO 2 H 2 S H 2 SO 4 Sulfur is under oxygen; think of H 2 O Sulfur is in the 3 rd period: it can have an expanded octet Can you draw other valid Lewis structures for HNO 3 ?

13. 2.4 The Nature of Light Low E High E Wavelength ( ) = distance traveled between successive peaks (nm). Frequency ( ) = number of waves passing a fixed point in one second (waves/s or 1/s or s -1 or Hz).

14. The Electromagnetic Spectrum 2.4 The various types of radiation seem different to our senses, yet they differ only in their respective and 

15. Fig. 2.5

16. Visible: = 700 - 400 nm R O Y G B I V Infrared (IR) : longest of the visible spectrum, heat ray absorptions cause molecules to bend and stretch. Microwaves: cause molecules to rotate. Short  range: includes UV (ultraviolet), X-rays, and gamma rays. Decreasing wavelength 2.4

17. 2.5 The energy of a photon of electromagnetic radiation is calculated by: E = h  where h = 6.63 x 10 -34 J. s (Plank’s constant) The wavelength and frequency of electromagnetic radiation are related by: c = where c = 3 x 10 8 m/s (the speed of light) Energy and frequency are directly related- higher frequency means higher energy.

18. UV radiation has sufficient energy to cause molecular bonds to break 2.5 What is the energy associated with a photon of light with a wavelength of 240 nm? C = = C  x 10 8 m/s E = h 240 nm x nm 10 - 9 m = 1.3 x 10 15 s -1 E = (6.63 x 10 -34 J. s) (1.3 x 10 15 s -1 ) E = 8.6 x 10 -19 J

19. 2.6

20. 20 UV index

21. 21 Stratospheric Ozone Equilibrium between oxygen and ozone (Chapman Cycle Fig 2.10) This implies that ozone concentrations remains constant in our stratosphere. Then why ozone layer is being depleted?

22. The Chapman Cycle 2.6 A steady state condition ≤ ≤

23. 2.7 Biological Effects of Ultraviolet Radiation The consequences depend primarily on: 1.The energy associated with the radiation. 2.The length of time of the exposure. 3.The sensitivity of the organism to that radiation. An Australian product uses “smart bottle” technology; bottle color changes from white to blue when exposed to UV light. The most deadly form of skin cancer, melanoma, is linked with the intensity of UV radiation and the latitude at which you live.

24. 24 Fig. 2.11

25. 25 Fig. 2.12 Incidence of Melanoma in the U.S.

26. First, UV radiation breaks a carbon-halogen bond: Photon  < 220 nm) + CCl 2 F 2. CClF 2 + Cl. (free radicals) 2.9 How CFCs Interact with Ozone

27. 2.9 2Cl. + 2O 3 2ClO. + 2O 2 2 ClO. ClOOCl The chlorine radical attacks an O 3 molecule: Then two chlorine monoxide radicals combine: UV photon + ClOOCl ClOO. + Cl. ClOO. Cl. + O 2 The ClOOCl molecule then decomposes: The net reaction is: 2 O 3 3O 2 The Cl. radicals are free to attack more O 3 The Cl. radicals are both consumed and generated; they act as catalysts

28. 2.9 Experimental analyses show that as ClO. concentrations increase, ozone concentration decreases.

29. 2.9 HCFCs are alternatives to CFCs: they decompose more readily in the troposphere so they will not accumulate to the same extent in the stratosphere.