Chapter 2 Protecting the Ozone Layer. The Ozone Hole

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1 Today (Tues 2/24) Newspaper Articles: Ciara Rodwell and Melissa Regan Intro to Ozone, Ozone Hole, & Chapter 2 Light, matter, and human health! Laboratory: Experiment 4 You design investigation Start Ozone Layer: Chemistry, Destruction, Weather, and Policy

2 Chapter 2 Protecting the Ozone Layer The Ozone Hole

3 Learning Objectives Ozone depletion and the ozone hole What is it, what is the status What causes it? Basic Chemistry Wavelength and frequency Atomic structure Molecules and models The ozone layer Effects of UV radiation Formation and destruction CFC and ozone reactions International Policy

4 Good vs Bad Ozone GOOD Stratrospheric Ozone Absorbs dangerous UV sunlight Being depleted km altitude BAD Tropospheric Ozone Photochemical Oxidant Smog

5 Light, Matter, and Human Health

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

7 The wavelength and frequency of electromagnetic radiation are related by: c = λν where c = 3 x 10 8 m/s (the speed of light) Wavelength and frequency are indirectly relatedhigher frequency means lower wavelength. The energy of a photon of electromagnetic radiation is calculated by: E = h ν where h = 6.63 x J. s (Planck s constant) Energy and frequency are directly relatedhigher frequency means higher energy. 2.5

8 What is the energy associated with a photon of light with a wavelength of 240 nm? c = λν E = h ν ν = c E = (6.63 x J. s) (1.3 x s -1 ) λ E = 8.6 x J ν = 3 x 10 8 m/s 240 nm x 10-9 m = 1.3 x s -1 nm 2.5

9 meters The Electromagnetic Spectrum: Wavelength 1 m = 10 9 nm 1 nm = 10-9 m The various types of radiation seem different to our senses, yet they differ only in their respective λ and ν. 2.4

Visible: λ = 700-400 nm R O Y G B I V Decreasingwavelength Infrared (IR) : longest of the visible spectrum, heat ray absorptions cause

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

The Electromagnetic Spectrum 2: Wavelength, Energy Frequency 10-11 10-30

11 The Electromagnetic Spectrum 2: Wavelength, Energy Frequency Energy (J) UV radiation has sufficient energy to cause molecular bonds to break

12 2.6

13 Fig. 2.7 Energy Distribution above the Earth s atmosphere Link to Figures Alive

14 Oxygen and Ozone absorbance O 2 O nm 200 nm 300 nm 400 nm 800 nm

15 Difference between O 2 and O 3? Allotropes Energy + 3 O 2 2 O 3 Energy must be absorbed (endothermic) for this reaction to occur. Ozone is an allotropic form of oxygen. An allotrope is two or more forms of the same element that differ in their chemical structure and therefore their properties. Element Allotropes oxygen O 2, O 3 carbon graphite, diamond, buckminister fullerenes 2.1

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.

16 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. 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. 2.7

17 Skin Cancer Rates

18 Fig. 2.12

19 Detecting and Analyzing Light Spectrometer Bead?

20 Design your investigation Questions: Where is UV and what materials are good at blocking it? How do the materials rank? Things to consider: Quantification Controls Multiple Trials?

21 For Thurs (2/26) Finish Reading Chapter 2 Start Homework #2 (Due 3/3)

22 Ozone Layer: Chemistry, Destruction, Weather, and Policy

23 Location of ozone layer.

24 Units for Ozone Measurement Dobson Units 1 Dobson = 1 part per billion of ozone in air. In the 1960 s ozone minima in Antarctica was about 300 Dobsons. In 30 years it has dropped to about 100 Dobsons.

25 Ozone depletion in Antarctica

26 How is Ozone Formed The Chapman Cycle Oxygen plus UV photon ozone Step 1: O > O + O Step 2: O 2 + O > O 3 The sunlight (UV) excites the oxygen molecules causing them to split into atomic oxygen. The released oxygen atom then combines with another oxygen molecule to form ozone.

27 Natural Ozone Destruction Chapman Cycle (cont d) Step 3: O 3 + UV photon > O 2 + O Step 4: O 3 + O > 2O 2

28 Chapman Cycle

29 How is Ozone Destroyed Unnaturally Mario Molina and F. Sherwood Rowland first proposed ozone depletion by CFCs CFCs..Chloro-Fluoro-Carbons. Spray cans, air conditioners, refrigerators, foams, fire extinguishers etc. Very controversial originally Won the Nobel Prize 1995 for this work Banned in industrialized countries, still used in developing countries

30 CFCs and ozone destruction Very stable - atmospheric residence times in the troposphere of 10 to over 100 years Eventually are mixed above the ozone in the stratosphere UVC breaks down CFCs to Cl free radicals (very reactive) Cl radicals destroy the ozone

31 Today (Thurs 2/26) Finish Ozone Layer: Chemistry, Destruction, Weather, and Policy Focus Group Activity Atoms, Covalent Bonds, and Lewis structures In-Class Worksheet #2

32 How CFCs Interact with Ozone First, UV radiation breaks a carbon-halogen bond: Photon (λ < 220 nm) + CCl 2 F 2. CClF2 + Cl. (free radicals) 2.9

33 The chlorine radical attacks an O 3 molecule: 2Cl. + 2O 3 2ClO. + 2O 2 Then two chlorine monoxide radicals combine: 2 ClO. ClOOCl The ClOOCl molecule then decomposes: UV photon + ClOOCl ClOO. + Cl. ClOO. Cl. + O 2 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 2.9

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

35 Fig Arctic vs. Antarctic

36 Polar Stratospheric Clouds Under extreme cold, with no wind, PSCs can form. On the surface of the PSC, safe molecules are converted to reactive species. Reactive species react with O 3.

40 Some interesting NASA links NASA video on ozone hole: About the NASA spacecraft for measurements: NASA s site on air pollution and Beijing Olympics

41 International Policy Montreal Protocol Int l agreement signed in 1987 More stringent in 1990, 1992, and 1997 Black Markets Substitutes replace one or more of the halons with hydrogen Less stable

42 Impact of Policy

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

44 Summary: Why is ozone depletion a problem? Increase UV radiation reaching the Earth s surface Increased skin cancers Impact plant growth What is UV radiation?

45 Focus Group Activity Pair up as assigned Read partner s paragraphs Discuss assignment with partner How did you think about pro-environment and smokestack sides? What challenges did you face when thinking about topic and this assignment? (Try to brainstorm solutions with your partners) Do your topics overlap? If so, how will you limit the overlap in your papers and presentations?

46 Atoms, Covalent Bonds, and Lewis Structures

47 Objectives Protons, neutrons, and electrons Atomic number = number of protons or electrons in an electrically neutral atom Mass number What is it? What does it tell you? Outer electrons What are they?; Why are they important; How do you use the periodic table to tell how many outershell electrons Isotopes two or more forms of an element that differ in number of neutrons Draw Lewis structures of atoms Draw Lewis structures of molecules

48 O Atomic number (Z) Mass number (A) (nuclear charge) -The number of protons and electrons in a neutral atom. -The sum of the protons and neutrons

49 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 2.2

50 The electrons in the outermost energy levels are called valence electrons. The group number (of the representative elements) on the periodic table tells you the number of valence electrons. Group 1A: 1 valence electron 1A Group 3A: 3 valence electrons 2A 3A 4A 5A 6A 7A 8A 2.2

51 Electronic arrangements

52 Lewis structures of atoms We represent atoms and valence electrons with Lewis structures N O B 5 valence electrons 6 valence electrons 3 valence electrons N O B What about C and Cl?

53 Representing molecules with Lewis structures: Typical valence for selected atoms = the # of bonds an atom typically forms Element H, X (X= F, Cl, Br, I) Typical valence Classification 1 monovalent O 2 divalent N 3 trivalent C 4 tetravalent 2.3

54 Molecular Structure Covalent bond a chemical bond where electrons are shared by atoms Octet rule general rule that in a molecule every atom is associated with 8 outer electrons (except H, which is associated with outer electrons) Lewis structures for molecules NH 3, H 2, Cl 2, O 2, N 2 Single bond, double bond, triple bond examples

55 Representing molecules with Lewis structures: Consider water, H 2 O: H O H 1. Find sum of valence electrons: 1 O atom x 6 valence electrons per atom = 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: H O H lone pair bonding pair 2.3

56 Try these; draw valid Lewis structures for: CO 2 O C O H 2 S H S H Sulfur is under oxygen; think of H 2 O NH 3 N H H H O HNO 3 O N O H Can you draw other valid Lewis structures for HNO 3? 2.3

57 Representing molecules with Lewis structures: Multiple bonds O O H C C H Double bond Triple bond 2.3

58 Resonance Structures Occasionally a single Lewis structure does not adequately represent the true structure of a molecule, so we use resonance forms: O O O O N O O N O O N O What about ozone, O 3?

59 For Tues (3/3) Homework 2 (Chapter 2) due Read lab handout Start reading Chapter 3 Start Homework 3 (due 3/17) For Next Week s Lab Protection from UV light paper due

Chapter 2: Protecting the Ozone Layer

Chapter 2: Protecting the Ozone Layer Chapter 2: Protecting the zone Layer Why do we need to do to protect the ozone layer? Isn t ozone hazardous to human health? Why is the ozone layer getting smaller? What can we do (if anything) to help