chap 8 full - CHEM 1A03: Intro. Chemistry I Review of Wave...

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1 CHEM 1A03: Intro. Chemistry I Essential Elements: Chemistry, Life & Health Ch.8: Electrons in Atoms Department of 1 Chemistry Chemistry that’s out of this world! Life on Mars? Odyssey Mission (Launch 2001): From space , mapped the amount/distribution of elements and minerals that make up the martian surface. Department of 2 Chemistry Maps of H distribution infer the presence of vast amounts of water ice buried beneath the surface in the polar regions. Current: Mars Phoenix Lander Mission (Launch: Aug. 4/07, Landing: May 25/08) Gamma Ray Spectrometer – detects an excited element’s characteristic emission of energy. Spectroscopy What is spectroscopy? The study of the interaction of radiation and matter What types of radiation? Department of 3 Chemistry Electromagnetic radiation What is electromagnetic radiation? Energy transmission propagated as waves with perpendicular magnetic and electrical components Petrucci, 9 th edition, p. 278 Review of Wave Properties & Light: Physics ν ∝ 1/ λ Wave properties: Figure 8-2 wavelength ( λ , nm) frequency (n, s -1 or Hz) amplitude Department of 4 Chemistry Wave Properties of Light: Interference - Fig. 8-5 Diffraction – Fig. 8-4b Refraction – Fig. 8-7a p. 279-283 Electromagnetic Spectrum (Fig. 8-3) Department of 5 Chemistry ν = c / λ , c = 2.997925 x 10 8 m/s in a vacuum i-Clicker Question#1 1. Does blue light have a longer/shorter wavelength than orange light? Department of 6 Chemistry 2. Is the frequency of red light greater/smaller than that of violet light? 3. Is the energy of yellow light greater/smaller than that of blue light?
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2 Sun’s Emission Spectrum Sun (T = 6,000K) Department of 7 Chemistry Earth’s Protective Shield: Ozone A. Ozone & UV Exposure UVB radiation (280-320 nm) from the sun is selectively absorbed by O 3 (ozone) in stratosphere Photolysis of O 3 absorbs 90% UV B radiation with peak at about 20km from Earth’s surface Department of 8 Chemistry Lower O 3 levels increase the transmittance of UV B radiation from the sun to earth Æ Montreal Protocol: 1987 From Sun To Earth Surface O 3 (g) O 2 (g) + O (g) Altitude (km) + Heat h ν = 280 – 320 nm Mt. Everest 8.8 km Ozone Depletion & UV Exposure B. Biological Impacts • UV B radiation can ionize biological molecules (DNA, Protein) Chronic exposure to UVB transmission increases chance of skin cancer, cataracts & genetic mutations • Body’s response: produce melanin (dark pigment) to filter UV Department of 9 Chemistry B radiation. O O - NH3 + HN Tryptophan (Trp) Aromatic Amino Acid in Protein N N N N NH 2 O OH OH HO Adenosine (A) Aromatic Base in RNA/DNA or H UV Exposure & Sunscreen C. Chemistry of Sunscreen • Propose alternative ways to decrease exposure to UV radiation? • Use of sunscreen/cosmetics containing UV absorbing chemicals UV B 2 Major Chemical Sunscreens: Department of 10 Chemistry UV A Broad spectrum coverage λ Continuous vs. Discontinuous Spectra • Continuous: e.g. visible spectrum Department of 11 Chemistry • Discontinuous: e.g. visible Na emission lines 589.0, 589.6 nm p. 283 Atomic spectra Discontinuous (Line) spectra of atoms ; few λ – Observed by experiment (Fig. 8-8)
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chap 8 full - CHEM 1A03: Intro. Chemistry I Review of Wave...

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