Topics for Today

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

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

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. Reflected Absorbed Transmitted Light Can Be…

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. Visible light ~600 nm + O. NO2 NO

12. Where else will we see absorption of light? UV <242 nm O2 2O.

13. Lab Next Week!!

14. Spectrophotometry

15. Spectrophotometry Measures the spectrum of light

16. Spectrophotometry Measures the spectrum of light How does spectrophotometry work?

17. Spectrophotometry Detector Sample (Absorbs Light) Light Source

18. The Spectrophotometer Detector

19. The Spectrophotometer Detector

20. This spectrophotometer has two light sources!

21. This spectrophotometer has two light sources! • 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. Sample Cuvette • The sample holder

25. The Spectrophotometer Detector

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

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

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

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 What do sunscreen and the ozone layer have in common? • Properties of Light • Sunscreen and the Ozone Layer! • Quiz #4

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

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

35. ULTRAVIOLET RADIATION UV-C UV-B UV-A VISIBLE 200 nm 280 nm 320 nm 400 nm Which is the lowest energy? Where is visible light?

36. ULTRAVIOLET RADIATION UV-C UV-B UV-A 200 nm 280 nm 320 nm 400 nm

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

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

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. Yes, some… Octinoxate (5.25%) Does sunscreen absorb UV-A? 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. Reflected Absorbed Transmitted Fluorescence What is going on here? Which is it?

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