1. Topics for Today Properties of Light Sunscreen and the Ozone Layer! Quiz #4

2. Readings for Today What is the difference between UV-A, UV-B, and UV- C? Section 2.4 Waves of Light Section 2.7 Biological Effects of Radiation! Spectro- photometry : Figure 5.23!

3. Topics for Monday UV light and the Ozone Layer

4. Readings for Monday Section 2.6 The oxygen / ozone sunscreen Section 2.8 Stratospheric Ozone Destruction Section 2.10 The Antarctic Ozone Hole: A Closer Look

5. Assignment #2 We crashed the server!!!

6. Exam #2 MOVED! NOW March 16 (not March 9)

7. Topics for Today Properties of Light Sunscreen and the Ozone Layer! Quiz #4

8. Light Can Be… Reflected Transmitted Absorbed

9. Light can be absorbed! The amount outgoing light is LESS than the incoming light. Only for a particular energy (wavelength).

10. Do sunglasses absorb light? Where have we seen the absorption of light in Chem 108?

11. NO 2 + O.O. NO Visible light ~600 nm

12. O 2 2O. O 2 2O. UV <242 nm Where else will we see absorption of light?

13. Lab Next Week!!

14. Spectrophotometry

15. Spectrophotometry Measures the spectrum of light

16. Spectrophotometry How does spectrophotometry work?

17. Spectrophotometry Detector Light Source Sample (Absorbs Light)

18. The Spectrophotometer Detector

19. The Spectrophotometer Detector

20. This spectrophotometer has two light sources!

21. 1) The UV Source Deuterium lamp Hmmm… What must be true of the quartz casing?

22. This spectrophotometer has two light sources! 2) Visible Source Halogen Lamp

23. The Spectrophotometer Detector

24. The sample holder Sample Cuvette

25. The Spectrophotometer Detector

26. Measures the light at each wavelength that passes through the sample! And this leads to…

27. The Spectrum! The computer output that allows us to visualize how much light was absorbed (or transmitted) at each wavelength. Wavelength (nm) Absorbance

28. Figure 2.7 p. 76 What is a nanometer ?

29. 1 nanometer (nm) = 1 x 10 -9 meters = 1 billionth of a meter. 1 nm is to 1 meter as 1 foot is to 190,000 miles!

30. Topics for Today Properties of Light Sunscreen and the Ozone Layer! Quiz #4 What do sunscreen and the ozone layer have in common?

31. What is UV-A and UV-B? What does the SPF # mean?

32. SUN ALERT: Limiting sun exposure, wearing protective clothing, and using sunscreens may reduce the risks of skin aging, skin cancer, and other harmful effects of the sun The fine print…

33. Octinoxate (5.25%) Oxybenzone (3.4%) What energy does it absorb?

35. Where is visible light? 200 nm400 nm VISIBLEVISIBLE ULTRAVIOLET RADIATION UV-AUV-BUV-C 320 nm280 nm Which is the lowest energy?

36. 200 nm400 nm ULTRAVIOLET RADIATION UV-AUV-BUV-C 320 nm280 nm

37. UV-A Wavelength = 320 – 400 nm Responsible for suntan What is a suntan?

38. An increase in melanin in your skin Melanin=Pigmentation=Suntan! Why does your body produce melanin when exposed to UV? PROTECTION from the UV radiation!

39. Penetrates deeply into the skin (low energy) Causes “premature aging” in skin (wrinkles)

40. Although, there are ways to “reverse” the aging process… ?

41. Octinoxate (5.25%) Does sunscreen absorb UV-A? Yes, some… UVA

42. Even careful tanning kills skin cells, damages DNA and causes permanent changes in skin connective tissue which leads to wrinkle formation in later life. There is no such thing as a safe tan.

43. UV-A Burns your eyes. Effects usually are temporary Chronic Exposure can result in a damaged retina or cataracts.

44. UV-A “Black” Light

45. Rocks and Minerals

46. Optical Brighteners! blue light + yellow light = white light! white light!

48. Fluorescence What is going on here? Reflected Transmitted Absorbed Which is it?

49. A two-step process!! 1) Incoming wavelength is absorbed 2) Light of a LOWER energy is re-emitted Fluorescence