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Chem 161-2010 Lecture 13

Chem 161-2010 Lecture 13 - CHEMISTRY 161-2010 LECTURE 13...

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CHEMISTRY 161-2010 LECTURE 13 ANNOUNCEMENTS E-MAIL ATTENDANCE EXAMS Chem 161-2010 Lecture 13 1
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PLAN FOR TODAY : H&P Chapters 7.5 – 7.7: THE WAVE NATURE OF LIGHT Electromagnetic waves The electromagnetic spectrum Continuous and Line Spectra PHOTONS Planck’s Quantum Hypothesis The Photoelectric Effect: Einstein and Photons BOHR’S HYDROGEN ATOM Bohr’s explanation of line spectra Line spectrum of hydrogen Ground states and excited states Chem 161-2010 Lecture 13 2
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Chem 161-2010 Lecture 13 3 ELECTROMAGNETIC WAVE WITH ELECTRIC FIELD IN ONE DIRECTION AND MAGNETIC FIELD PERPENDICULAR TO IT, BOTH FIELDS MOVING AT THE SPEED OF LIGHT
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LIGHT AND MATTER ET: A wave is what you see when you drop a pebble in water. Describe light wave as electromagnetic radiation with a magnetic field, an electric field, and having a speed of 3 x 10 8 m/s. Draw undulating light curve to define λ, υ and amplitude. Relate light to graph on next page. ET: Discuss 3 equations from formula page and show that knowing one parameter gives the other two Wavelength = λ = distance/cycle = distance between corresponding points in the wave. Frequency = υ = cycles/s = cycles s -1 = s -1 = Hz = the amount of time it takes for 1 wavelength to pass a given spot. Amplitude = intensity, brightness, related to no. of photons emitted E photon = hυ ET: Use water waves to show relationship between high frequency and high energy; also use graph on next page. (E multiple photons = nhυ) (E mole of photons = 6.022x10 23 hυ) υλ = c light E photon = hc/λ h = 6.626 x 10 -34 Js = 6.626 x 10 -34 kgm 2 s -2 s = 6.626 x 10 -34 kgm 2 s -1 c light = 3 x 10 8 m/s DeBroglie theorem: λ= h/mv ET: Wave-particle duality (wave: light refracts when going through a prism; particle: behaves like bowling balls); tie into E = hυ m is the mass in kg v = velocity in meters per second Bohr atom: E = -B/n 2 ΔE = (-B/n f 2 ) – (-B/n i 2 ) = B((1/n i 2 ) - (1/n f 2 )) = -B((1/n f 2 ) - (1/n i 2 )) B = Bohr magneton = Rydberg constant = 2.179 x 10 -18 J Einstein’s photoelectric effect Total Energy = Energy threshold* + Energy kinetic Energy total = h υ threshold + h υ kinetic energy *Energy threshold = Work function Chem 161-2010 Lecture 13 4
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Chem 161-2010 Lecture 13 5 H i g h e n e r g y L o w e n e r g y
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Chem 161-2010 Lecture 13 6 BOHR HYDROGEN ATOM Electron Excitation via light abs. Electron Relaxation via Light Emission Nucleus Ground state Electrons in excited states will eventually emit energy as the electron drops down to one of the lower energy levels and eventually to the ground state.
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Siegel’s 2010 notes: If ripples in a pond are 1 cm from crest to crest and lap at the shore at the rate of 1 wave every 2 s, what is the speed of the wave?
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