Sp06Exam2-Key+simp - CHEM 260 Second hot?xam June 5, 2006...

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Unformatted text preview: CHEM 260 Second hot?xam June 5, 2006 PRINT NAME / é? \ 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 111., = the mass of the proton = 1.67 x 10'27 kg e' = 1.60 x 10'” coulombs lama = 1.67 x 10"” kg Question I multiple choices (10%) Circle the letter corresponding to the best answer to each of the multiple choice questions. 1. Of the following, the electromagnetic radiation with the least energy is: @radio waves b. gamma rays c. X—rays d. ultra violet light 6. visible light 2. An atomic orbital whose azimuthal or orbital quantum number is 3 is: a. an s orbital b. a p orbital c. a d orbital an f orbital e. a g orbital 3. The Pauli exclusion principle states that: a. It is impossible to simultaneously measure a particle's position and momentum to arbitrary precision b. the probability of finding an electron in an atom is proportional to ‘41de In an atom, no two electrons can have the same four quantum numbers . light is absorbed or emitted discontinuously e. electrons will always enter orbitals in such a way that the atom's spin quantum number is maximized 5. The set of quantum numbers for an electron in an orbital that is not allowed is: a.n=2,f=1,m=0,s= U2 b.n=3,I=2,m=1,s=1f2 @n=2,l=2,m=0,s=lf2 . =2,i=o,m=0,s:-u2 41 2 m 6. According to the "aufbau" principle, the number of unpaired electrons in an atom of carbon, at. no. 6, is; a. 0 b. 1 ©2 d. 3 e. 4 7.. The scientist who invented molecular orbital theory and received an unshared Nobel Prize for his work was: a. Max Born b. Niels Bohr @a Robert Mullikan d. Linus Pauling e. G.N. Lewis 8. 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 c. Robert Mullikan Linus Pauling e. (1N. Lewis 9. 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. H; and HCl b. N2, CH3CH3,CH3C1 Q) H20, CH3Cl, co2 (1. CH4, H2, N2 10. 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 d. Pressure Broadening All of the above m Question II (20%) Write with large clear letters the word “TRUE” or the word “FALSE” next to each of the following statements. 1. The ls ele on in both sodium and uranium occasionally tunnels through its respective nucleus. Vt 2.The granddaughter of Max Born is Olivia Newton John 773 U K 3A natural phenomenon that does not obey the Boltzmann distribution lavv is the distribution of cations around a negatively charged electrode. F A L b (1; 4.A fundamental difference between classical mechanics and quantum mechanics is that in quantum mechanics a particle has a trajectory, but in classical mechanics it does not haveatrajectory. F/q L SE 5.According to the Heisenberg Uncertainty Principle, it is impossible to measure a photon’s energy without some time elapsing. 72E U 1" 6 . Combining atomic orbitals such as a 23 and three 2p orbitals to form 45p3 hybrid orbitals is a tenet of valence bond theory. 77? (J E 7. Both valence bond theory and molecular orbital theory predict that H62 does not exist at room temperature—IE U E 8. Based on the magnetic quantum number, the multiplicity of the ground state of a single nitrogen atom is 3 F9 L 6 E 9. Based on the spin uantum number, the multiplicity of the ground state of a single carbonatomis3 fUE ,2 ) z 3 10. Nuclear vibrations in a molecule take place very much quicker than electronic transitions L 55 11. The intensi of an electronic absorption is proportional to the Frank-Condon Factor 7— C) if 12. The photons emitted or absorbed during an electronic transition have an energy around 100 kJr'mol 773 a g ( z 5 I, 1.2 [0 a A (7/;er / 3 13. In order for a population inversion to occur, as in a ruby lasherjor example, the Boltzmann distribution law requires a negative temperature. g 16 U E 14. A chlorine molecule would be expected to have a vibrational Raman spectrum ZZ§ 05 15. All Fermions have half-integral spins Tflu/g 16. In most atoms, 5 -)p transitions are forbidden FA 4 5/3 17. In naturally occurring HCl gas, the system’s P branch of the IR spectrum consists of a series of two closely spaced lines. 2/2 U f 18. In most atoms and molecules, S -)D transitions are allowed FA Z ‘55 K 5—H?) 13' 4 x.) j 19. In most atoms, a 15 to 23 transition is allowed 1"? C5 (E 20. In naturally occurring HCl gas, the system’s Q branch of the IR spectrum is the most intense peak. F4 L S E Question III(22%) Fill in the blan k . 1. The word LASER is an acronym or GMQA é : c 4'14 Off J74'MUA 745/ Gin/551‘”? 9 I‘d ’4 man 2. The spectral line of T in a distant star was found to have shifted from 654.2 nm to 740 nm . Is he distant star receding from the earth or approaching the earth? (pm! 554/ f'ec: 11:7 3. In photochemistry, when spontaneous emission continues on, sometimes for many hour , after the exciting radiation is turned off, the process is called We: 4. In the equation flg‘ = [will wd‘t, llg is called the %M”,SI 74M IMch/- 5. In photochemistry, when spontaneous emission ceases immediately after the exciting radiation stops, the process is called 3&200/ggmcc 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 00/)? /c, I" 7. The reason why a homonuclear diatomic molecule such as N32 is Rgn active is that its Raman selection rule depends upon a change in WA e molecule 8. Which of the following molecules may show a are rotational inicrowave absorption spectrum? H2,HC1,CH4,CH3CI,CH2C12 i I I c 55 (L l C All c/L 9. N; has many properties similar to the element , ( a r .5; /: 60’? ) 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 *Question IV (9%) A quartz cell 2.0-mm wide was filled with a solution of benzene dissolved in a non- absorbing solvent and placed in a UV-vis Spectrophotometer. The concentration of benzene was 0.010 M and the wavelength of the radiation at the absorption maximum was 256 nm. Calculate the molar absorption coefficient of benzene at this wavelength given that the transmission was 48 %. ( I 0/0 ) This calculation is based on jgr'é Law. If the solvent did absorb some radiation, albeit with )me at a different wavelength, how would you modify the experiment? . c2. cl ... loam—T T. logm(EI—a)=loj‘o(‘-l?) ) 0114:“— looC 00,5: 1 {DEE—— MO\MM 239C! aura“) *Question V(9%) DM‘ESrZSV‘ ": ’Pk The wave number of the fimdamentizbration frequency [(voévl),AJ =0] of the diatomic molecule 7S'BrslBr is 323.2 cm". Calculate the force constant of the bond and express your answer in newtonsfmeter. Would you expect this spectrum to be very intense or very weak? Why? Q):QW3JJU:|QJ BTW u ;._'.. is. to \J =C§JU :3Xl0cix3236 '4 arr JLL sec Q I .—.-. Cl-equ Sec." 1. l k v z: 2—.—_... HIT'JX ll 12 (Q-é‘l mo sec" .2- Q-qum 5. (Sec); film The SPeC‘l-rum coy“ IR (Selma fife rut-“63 r \J a 5 P rac-l-tcall “AB (5/1 Chaflge be Vef‘ cl: Och <l y ouer \ilCCCLQSf o\c__ Women-j” E meme/)4 .. 1 Pa Question VI (12%) Using the energy level diagram shown below, draw the electronic configuration of the homonuclear diatomic molecule, N2. 2po* Based on your diagram, what is the bond order of N2? [2%)80: ‘0‘"q :: 3 Based on your diagram, is N2 paramagnetic or diamagnetic? Clo/o) cltdm At‘l‘lL N Based on your diagram, what is he spin multiplicity £52 1n its ground state ? 0'70 230 +I 1| San lc‘l' Using the same “aufbau” that you used for N2 on which to base your deci on, is the singlet state of oxygen gas more or less energetic than the triplet state? Why? g‘olo more. cncm‘eht - Hue single-L s—lcri: VlOleJ Huncl's rule. 8 0 5 S ’ ‘9 GEL-{\FF J Question VII (8%) Calculate the mean or “average” value of the radius of the ls orbital in a hydrogen atom using the following values of the component wave functions. Express your answer in meters. R(r) = 2(1/a0)3’2 e'pm, where p = 2r/a0 and a0 is the Bohr radius. @(9) = (1/2)”? (m ) = um)”. Hint: the mean radius is nothing more than the value of the radius given by the equation; <r> = ir/lp/ZST where 5’: = 47tr2dr and All/2 is the square of the composite wavefunction The integral ,ix“e'“dx = n!!(a"+') will be of use and n! is “n factorial” R(P)e(e)¢(CP) = WOUQ'WP) x . '5‘ a : c MW] [ii/WI “+2: [1+ (24‘: Question VIII (5%) In the box below, explain whatis meant by the Frank-Condom Principle. If possible, use a small diagram. Do not write outside the box \ "he. ‘“Clark! 3 C1 .'. OM €233.93; as \lq’unp)mawe. {‘unc’flom seleryme. uv—«r-s ( crud-m rm: 5 CA'PC" zm-gf‘qfl'se- ‘l‘e has +5 md a. st Air "'3" Mn 'Hfle e‘XCI S—la-l-c (or .sunaJcm'le ) 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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Sp06Exam2-Key+simp - CHEM 260 Second hot?xam June 5, 2006...

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