Protecting the Ozone Layer

1. Protecting the Ozone Layer

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

3. The Ozone Layer • Ozone, O3, is a health hazard in the troposphere, but essential to life on earth in the stratosphere.

4. The Ozone Layer • Ozone, O3, is a health hazard in the troposphere, but essential to life on earth in the stratosphere. Energy + 3 O2 2 O3 Energy must be absorbed (endothermic) for this reaction to occur.

5. Ozone Formation Energy + 3 O2 2 O3 Energy must be absorbed (endothermic) for this reaction to occur. Ozone is anallotropicform of oxygen. An allotrope is two or more forms of the same element that differ in their chemical structure and therefore their properties. ElementAllotropes oxygen O2, O3 carbon graphite, diamond, charcoal

6. The Regions of the Lower Atmosphere Atmospheric pressure changes with altitude

7. The Regions of the Atmosphere Altitude record for plane flight – 31,000 m by an SR-71 on its retirement flight. Why does it take longer to cook an egg in Denver than it does in New Orleans? There is less air pressure at higher altitudes. Water boils when the vapor pressure of the water molecules exceeds that of the localized air pressure. Because there is less air pressure at higher altitudes, more energy must be supplied (longer time) to get the temperature of the water high enough to cook the egg.

8. The ozone layer is a region in the stratosphere with maximum ozone concentration.

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

10. Isotopesare 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: 12C 13C 14C

11. Isotopesare two or more forms of the same element (same number of protons) whose atoms differ in number of neutrons, and hence in mass. Hydrogen has exactly three isotopes – 1H – Majority isotope in nature. Hydrogen 2H – Deuterium. Only about 0.0026 - 0.018% in nature. Stable. Sometimes called heavy hydrogen. 3H – Tritium. Half life of only 12 years, so only trace amounts in nature. Radioactive, but only weakly, and not harmful to humans externally. Used in watch dials.

12. Isotopesare two or more forms of the same element (same number of protons) whose atoms differ in number of neutrons, and hence in mass. Uranium has three main isotopes – 238U – Majority isotope in nature. Radioactive, but not capable of uncontrolled fission – can’t make a bomb. 235U – Only about 0.7% in nature. Enriching to 4% allows nuclear power. Enriching to >50%, it can explode. 233U – Only about 0.005% in nature. Not as strong a slow neutron source as 235U, but more than 238U

13. Let’s go back to the Periodic Table

14. The Bohr Model • This is a MODEL of the atom that links electron behavior (microscopic) to the periodic law (macroscopic).

15. Let’s go back to the Periodic Table

16. Valence Electrons • Valance Electrons • Electrons in the Outermost Principal Shell • Which simply means the electrons that fill the orbitals for the main-group elements • That means there are always a maximum of either two (first row) or 8 (all the others) • Electrons Involved in Chemical Bonding

17. Valence Electrons

18. Valence Electrons

19. The group number (of the representative elements) on the periodic table tells you the number of valence electrons. Group 1A: 1 valence electron 1A 8A Group 3A: 3 valence electrons 3A 6A 7A 4A 5A 2A

20. Representing molecules withLewis structures: Consider water, H2O:

21. Representing molecules withLewis structures: Consider water, H2O:

22. Representing molecules withLewis structures: Consider water, H2O: • 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

23. Representing molecules withLewis structures: Consider water, H2O: • 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:

24. Representing molecules withLewisstructures: Typical valence for selected atoms = the # of bonds an atom typically forms

25. Representing molecules withLewisstructures: Multiple bonds Doublebond Triplebond Occasionally, a single Lewis structure does not adequately represent the true structure of a molecule, so we useresonanceforms:

26. Light and Matter • Light has a very important connection to all this. • Light interacts with matter by either being reflected or absorbed.

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

28. The Electromagnetic Spectrum The various types of radiation seem different to our senses, yet they differ only in their respective l and n.

29. IncreasingEnergy ROY GBIV Decreasingwavelength Microwaves: cause molecules to rotate. Infrared (IR): longest of the visible spectrum; heat absorptions cause molecules to bend and stretch. Visible: l = 700–400 nm Short l range: includes UV (ultraviolet), X-rays, and gamma rays.

30. The wavelength and frequency of electromagnetic radiation are related by:c = ln where c = 3 x 108 m/s (the speed of light) The energy of a photon of electromagnetic radiation is calculated by: E = hn where h = 6.63 x 10–34 J.s (Planck’s constant) Energy and frequency are directly related –higher frequency means higher energy.

32. The Chapman Cycle

33. The Chapman Cycle

34. The Chapman Cycle l≤ + l≤ A steady state condition +

35. The Chapman Cycle l≤ + l≤ A steady state condition +

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

37. How CFCs Interact with Ozone CFC-11 CFC-12 Freon 11 Freon 12 trichlorofluoromethane dichlorodifluoromethane CCl3F CCl2F2 First, UV radiation breaks a carbon-halogen bond: Photon (l < 220 nm) + CCl2F2 .CClF2 + Cl. (free radicals)

38. The chlorine radical attacks an O3 molecule: 2 Cl. + 2O3 2 ClO. + 2 O2 Then two chlorine monoxide radicals combine: 2 ClO. ClOOCl The ClOOCl molecule then decomposes: UV photon + ClOOCl ClOO. + Cl. ClOO. Cl. + O2 The Cl. radicals are free to attack more O3 The Cl. radicals are both consumed and generated; they act as catalysts The net reaction is: 2 O3 3 O2

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

40. Change in size of the ozone hole over for last decade

41. Another look at the ozone hole. The more blue, the worse the problem….

44. HCFCs are alternatives to CFCs: they decompose more readily in the troposphere so they will not accumulate to the same extent in the stratosphere. HCFC-141b HCFC-22 dichlorofluoroethane chlorodifluoromethane C2H3Cl2F CHClF2

45. Refrigerants for Automobile Use Freon in your car’s air conditioner is a commonly used CFC