CH969E~1 - CHEM 161-2007 CHAPTER 7 LIGHT AND ATOMIC...

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Unformatted text preview: CHEM 161-2007 CHAPTER 7 LIGHT AND ATOMIC STRUCTURE PRACTICE PROBLEMS DR. ED TAVSS Light and matter Bohr hydrogen atom Quantum mechanics/DeBroglie wave-particle duality/Plancks equation/Photoelectric effect Quantum nos./orbitals 1 LIGHT AND MATTER CHAPTER 7 ATOMIC STRUCTURE LIGHT AND MATTER 20. What is the mass-to-charge ratio for 27 Al 3+ ? The charge on an electron is 1.602 x 10 19 C. A. 2.8 x 10 7 kg/C B. 3.1 x 10 8 kg/C C. 8.8 x 10 11 kg/C D. 4.7 x 10 9 kg/C E . 9.3 x 10 8 kg/C One would assume that the mass to charge ratio is grams of a mole of Al per number of electron change, is 27:3 = 9gAl/electron. However, the convention for mass-to-charge ratio is mass of an atom (in kg)/charge (in Coulombs). -1.602 x 10-19 C = the electric charge on one electron. (27 g/mol x (1 kg/1000 g)x(1 mol/6.022 x 10 23 atom))/((1.602x10-19 C/electron) x (3 electrons)) = 9.33 x 10-8 kg Al/C CHAPTER 7 ATOMIC STRUCTURE LIGHT AND MATTER 11. A laser produces a light of wavelength 575 nm. How many photons of this light would have to strike a material for the material to absorb 55.1 kJ? A . 1.59 x 10 23 B. 5.31 x 10 22 C. 3.45 x 10 20 D. 6.36 x 10 23 E. 2.76 x 10 22 E photon = hc/ h = 6.626 x 10-34 Js c = 3 x 10 8 m/s E photon = ((6.626 x 10-34 Js) x (3 x 10 8 m/s))/(575 nm x (1 x 10-9 m/nm)) = 3.457 x 10-19 J/photon 55100J/(3.457 x 10-19 J/photon) = 1.59 x 10 23 photons 2 ZUMDAHL 5 TH EDITION CHEM 161-2002 RECITATION 8 TH WEEK CHAPTER 7 - LIGHT, ATOMIC STRUCTURE AND PERIODIC TABLE TRENDS LIGHT AND MATTER 7-37 The laser in an audio compact disc player uses light with a wavelength of 7.80 x 10 2 nm. Calculate the frequency of this light. c = c = 3 x 10 8 m/s = c / (3 x 10 8 m/s)/(780 nm x (1 x 10-9 m/nm)) = 3.85 x 10 14 s-1 3 ZUMDAHL 5 TH EDITION CHEM 161-2002 RECITATION 8 TH WEEK CHAPTER 7 - LIGHT, ATOMIC STRUCTURE AND PERIODIC TABLE TRENDS LIGHT AND MATTER 43 It takes 7.21 x 10-19 J of energy to remove an electron from an iron atom. What is the maximum wavelength of light than can do this? E photon = h c = c = 3 x 10 8 m/s h = 6.626 x 10-34 Js =hc/E ((6.626 x 10-34 Js) x (3 x 10 8 m/s))/( 7.21 x 10-19 J) = 2.75 x 10-7 m 4 BOHR HYDROGEN ATOM 22 Chapter 7 Light and Atomic Structure Bohr hydrogen atom What is the wavelength of light emitted when an electron in the third energy level goes down to the ground state in the hydrogen atom? A . 103 nm B. 205 nm C. 421 nm D. 630 nm E. 821 nm E = -B((1/(n f ) 2 ) (1/(n i ) 2 )) E = -(2.179 x 10-18 ) x ((1/(1) 2 ) (1/(3) 2 )) = -1.937 x 10-18 J = hc/E = ((6.626 x 10-34 Js) x (3 x 10 8 m/s))/(1.937 x 10-18 J) = 1.026 x 10-7 m 1.026 x 10-7 m x (1x10 9 nm/m) = 102.6 nm A HILL & PETRUCCI CHAPTER 7 ATOMIC STRUCTURE HYDROGEN ATOM AND THE BOHR MODEL 13. A hydrogen atom electron in an excited state with n = 7 drops to a lower energy state of n = 3. What is the wavelength of the light emitted in this transition?...
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CH969E~1 - CHEM 161-2007 CHAPTER 7 LIGHT AND ATOMIC...

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