260_Exam_2_Sample - CHEM 260 Second hourly Exam Monday,...

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Unformatted text preview: CHEM 260 Second hourly Exam Monday, June 4, 2007 PRINT NAME first last STUDENT ID # “There are therefore Agents in Nature able to make the Particles of Bodies stick together by very strong Attractions. And it is the Business of experimental Philosophy to find them out.” Sir Isaac Newton (1705) “I can’t believe that!” said Alice .... ..one can’t believe impossible things.” “I dare say you haven’t had much practice said the Queen” “When I was your age I always did it for half an hour a day. Why sometimes I believed as many as six impossible things before breakfast” Lewis Carrroll “Through The Looking Glass” “I believe the chemical bond is not so simple as some people seem to think” Robert S. Mulliken (1938) TABLE I USEFUL DATA R = 8.31 J/Kmol = 0.082 litatm/Kmol One atm. = 760 mmHg = 1.01 x 105 Pa Boltzmann constant, k; = 1.38 x 10'23 J/K h = Planck's constant = 6.6 x 10'34'Jsec C = velocity of light = 3 x 108 m/sec me = the mass of the electron = 9.1 x 10'31kg mp = the mass of the proton = 1.67 x 10'27 kg e' = 1.60 x 10'19 coulombs 1amu = 1.67 x 10'27 kg Bohr radius =53 pm (1pm =1 x 10'12m) Question I multiple choices (4%) Circle the letter corresponding to the best answer to each of the multiple choice questions. *1.. The scientist who invented molecular orbital theory and received an unshared Nobel Prize for his work was: a. Max Born b. Niels Bohr c. Robert Mullikan d. Linus Pauling e. G.N. Lewis *2. The scientist who first discovered "the nature of the chemical bond", figured out the concepts of electronegativity and resonance, and is the only person ever to receive two unshared Nobel Prizes was: a. Albert Einstein b. Niels Bohr 0. Robert Mullikan d. Linus Pauling e. G.N. Lewis *3. One of the many triumphs of quantum mechanics is that it quantitatively accounted for the spectra of many different molecules. This is especially true when it came to selection rules that tell us which transitions are allowed and which transitions are forbidden. Of the molecules below, the series that exhibit an IR spectrum is: a. H2 and HCl b. N2, CH3CH3,CH3C1 C. H20, CH3Cl, C02 (1. CH4, H2, N2 *4. Spectral lines always have a finite width. That is, they cannot be arbitrarily narrow depending on the cost of your instrument. The reason for this is: a. The Heisenberg uncertainty principle. b. Doppler broadening c. Collision Broadening (1. Pressure Broadening e. All of the above Question II (16%) Write with large clear letters the word “TRUE” or the word “FALSE” next to each of the following statements. *1 .According to the Heisenberg Uncertainty Principle, it is impossible to measure a photon’s energy without some time elapsing. *2 . The vast majority of the scattered light in Raman spectroscopy does not change its frequency at all *3. Both valence bond theory and molecular orbital theory predict that Hez does not exist at room temperature. *4. Based on the magnetic quantum number, the multiplicity of the ground state of a single oxygen atom is 3 *5. Based on the spin quantum number, the multiplicity of the ground state of a single carbon atom is 2 *6. Nuclear vibrations in a molecule take place very much quicker than electronic transitions *7. The intensity of an electronic absorption is proportional to the Frank-Condon Factor *8. The photons emitted or absorbed during an electronic transition have an energy approximately 100 kJ/mol *9. In order for a population inversion to occur, as in a ruby laser for example, the Boltzmann distribution law requires a negative temperature. s *10. A chlorine molecule would be expected to have a vibrational Raman spectrum *11. A single electon in space has a spin quantum number of 1/2 *12. In most atoms, s 9p transitions are forbidden *13. In Raman spectroscopy, the scattered light whose energy has decreased is called anti-stokes radiation *14. In Raman spectroscopy, the anti-stokes lines are more intense than the stokes lines *15. In most atoms and molecules, S 9D or 2 9 A transitions are allowed *16. In hydrogen atoms, a ls to 2s transition is allowed Question III(24°A)) Fill in the blank 1. The word LASER is an acronym for 2. The spectral line of Ti8+ in a distant star was found to have shifted from 654.2 nm to 740 nm . Is the distant star receeding from the earth or approaching the earth? 3. In photochemistry, when spontaneous emission continues on, sometimes for many hours, after the exciting radiation is turned off, the process is called 4. In the equation ,uij = IMFLL Wd’t, LL17 is called the 5. In photochemistry, when spontaneous emission ceases immediately after the exciting radiation stops, the process is called 6. The change in frequency of electromagnetic radiation due to the source of the radiation moving toward or away from the observer is called the 7. The reason why a homonuclear diatomic molecule such as Nag is Raman active is that its Raman selection rule depends upon a change in of the molecule 8. Which of the following molecules may show a pure rotational microwave absorption spectrum? H2, HCl, CH4, CH3C1, CH2C12 *9. According to the United Atom theory, 02 has many properties similar to the element *10. The principle piece of information obtainable from the IR spectrum of a diatomic molecule is the *11. The principle piece of information obtainable from the microwave spectrum of a diatomic molecule is the *12. The penetration of a quantum particle such as an electron or a proton through classically forbidden barriers is called Question IV (9%) The molar absorption coefficient of seawater in the visible range is 6.2 x 10‘5 Lit/molcm. Calculate the depth to which a diver must dive to experience half the surface light ([I/IO] = 0.5). Hints: Drawing a picture of the diver below the ocean’s surface would help. Also, the molar concentration of seawater is approximately 5.5 M. Express your answer in meters. *Question V(9%) The rotational energy, Em = J (J+1)h2/8n21, where J is the rotational quantum number (J =0,1,2,3 . . .) and I is the moment of inertia, is the solution (eigen value) of the Schrodinger wave equation for the rigid diatomic rotor. The microwave spectrum of NO gave a series of lines, AEoel = 1.02 x 1011sec'1. From these data calculate the bond length of the NO molecule and express your answer in nanometers. Hint: B = h/8n21 *Question VI (16%) Using the energy level diagram shown below, draw the electronic configuration of the homonuclear diatomic molecule, 02. 2p0'* 2p1c* 2p1c* 3r W 2pc 286* 2so 186* ISO Based on your diagram, what is the bond order of 02? Based on your diagram, is 02 paramagnetic or diamagnetic? Based on your diagram, what is the spin multiplicity 02 in its ground state ? Is 02+ more, or less, stable thermally than 02? Question VII (8%)Show all work Calculate the mean or “average” value of the radius of the ls orbital in a He+ atom using the following values of the component wave functions. Express your answer in meters. R(r) = 2(z/ao)3/2 6"”, Where p = 2r/a0 and a0 is the Bohr radius. 8(9) = (1/2)“2. (13(0) = (1/211)1/2.z = charge on the He+ Hint: the mean radius is nothing more than the value of the radius given by the equation; <r> = him/2512 Where 512 = 41t1’2d1‘ and All/2 is the square of the composite wavefunction, \|l = R(r) @(9)CI)(°) -ax The integral l x“e dx = n!/(a"+1) will be of use and n! is “n factorial” In the space below, sketch the graph of the Ilium vs. I for the Is orbital of He+ Question VIII(9°/o) A. In the space below, using Lewis structures, draw ethylene, C2H4 B. Using Valence Bond theory, including hybridization, draw the structure of ethylene in the space below. Label ’11: bonds and 6 bonds and approximate bond angles. C. List three major tenets, or assumptions, of VB theory. D. The first people to think about chemical bonding, from a quantum mechanical point of View, were two German physicists, Heitler and London who, in 1927, immediately after Heisenberg published his uncertainty principle, tried to solve the R- = 00 problem (what happens when atoms are infinitely far apart, but still “know enough”to form a chemical bond). In fact, Pauling was collaborating with these guys when he figured out VB theory. As we all know, the R=0 problem was solved by AC. Wahl who thought of the united atom concept, but the R = 00 problem has still not been solved!!!!!! In the space below, briefly indicate why this is such a difficult problem to solve. (Do not try to solve this problem —even U of M kids would have trouble with this) Do not write outside the box. Question IX (5%) In the box drawn below, explain why the analogy “Electrons settle in excited states for essentially the same reasons Norwegians settled in Minnesota” is essentially true. Do not write outside the box. 10 ...
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This note was uploaded on 06/01/2008 for the course CHEM 260/261 taught by Professor Davids.newman during the Spring '06 term at University of Michigan.

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260_Exam_2_Sample - CHEM 260 Second hourly Exam Monday,...

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