chem04 - W (a) Construct the molecular orbital energy level...

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Unformatted text preview: W (a) Construct the molecular orbital energy level diagram (correlation diagram) for F2. That is, draw energy levels for the atomic orbitals and show how they combine to form the molecular orbitals of F2. Show electron occupations for the F atoms and the molecule, F2. Label all A.O.'s and M.O.‘s (975 Problem #1 (worth 25 % of the grade on this exam) (b) Write out the resulting electron configuration for F2. I (fig) 2 QL(]7;;) 5" (c) What is the bond order for F2 as indicated by your MO scheme? Show your work. 50W 0/068 : szf-() = / 7 (d) Construct the MOS of Srz and show their electron occupations. (9%,... . .5? fr \\\ _@_ J8— . 9?”; (e) Give a molecualr orbital explanation as to why 02 is paramagnetic and N2 is not. 0; #49 ' ant/421w 83". N2 flog? A647? 0/3. V car-9L ,9 jars: /—6» ,, 96a \@ U: V c) é / 5’2”. 53» E _ (a) In VSEPR theory, what molecular geometries are, expected if the steric number, SN, of the central atom 18 2, 3, 4, 5, and 6? Here, assume that all bonds are equivalent and that lone pairs play no role. _;_9_/_1{ 7 W 3 ‘7" WM 6 0W Problem #2 (worth 20 %) mw/‘w amen/ear /‘J’ #47 Necerrfll)’ if Ml” flemfl/ffiow A? CAM/C _.—————-——-—‘I‘ (b) Predict the geometry of the following molecules and ions: (a) Clo; , (b) C10; , (C) SiH4, E5. (a) The central Cl atom has all of its valence electrons (six, because the ion has a net positive charge) involved in bonds to the surrounding three oxygen atoms and has no lone pairs. Its steric number, is 3. In the molecular ion the central Cl should be surrounded by the three 0 atoms in a trigonal planar structure. (b) The central Cl atom in this ion also has a steric number of 3, composed of two bonded atoms and a single lone pair. The predicted molecular geometry is a bent molecule with an angle somewhat less than 120°. (c) The central Si has a steric number of 4 and no lone pairs. The molecular geometry should consist of the Si atom surrounded by a regular tetrahedron of H atoms. (d) Iodine has seven valence electrons of which five are shared in bonding pairs with F atoms. This leaves two electrons to form a lone pair, and so the steric number is 5 (bonded atoms) + 1 (lone pair) = 6. The structure will be based on the octahedron of electron pairs from Figure 14—6, with five F atoms and one lone pair. The lone pair can be placed on any one of the six eduivalent sites and will cause the four F atoms to bend away from it toward the fifth F atom, giving the distorted structure shown in Figure 14-9. KE Consider the quantum mechanical, rigid rotor model for the rotation of a diatomic molecule. Problem #3 (worth 15 %) (a) As energy increases, what happens to the spacings between the J levels? ,_ \ 1/ mc/chJ’eJ (b) In order for a molecule to absorb energy that causes a rotational transition to occur, what condition must that molecule meet? I7 Week? 72’ fire /} WWW/7’ fl/yale flU/l/e/U— (c) What kind of electromagnetic radiation is typically required to induce rotational transitions? mam Va? ass; (d) If you make the assumption that their bond lengths are the same, for which of the following 7 two molecules is the energy of their 1:2 --> J :3 rotational transitions the larger, LiBr or HBr? Show your reasoning in detail. 115,19 6257 5! C532 "29:313.. /‘/v ['77/ W Z 3%, ware 4’: “m < AMI x 7% r" M” 3 11% < 1mm % M/ Consider the problem of molecular vibrations using the quantum mechanical, one-dimensional harmonic oscillator as a model. Problem #4 (worth 25 %) I (1’ (a) As energy increases, what happens to the energy 5 acings between the v levels? r , may 3 A)’ We Jame. (b) In order for a molecule to absorb infrared radiation that causes a vibrational transition to occur, what condition must that molecule meet? :7 M037 flare M are/ZMT/Wfl Wade 3 m A CAI/twfle M l . ‘ _ ‘ ' _ . _ , p/yage Maqe/W‘fl 9 ~ ~‘ ’ fifk‘ (c) What IS the selection rule for transmons in a harmomc oscfllator. I // [Ag/Wag: Av=¢/ (d) If you make the reasonable assumption that their bond strengths are the same, for which of the Eli};- following two molecules is the energy of the v=5 level the higher, H1 or DI? Show your reasoning indétail. E: (Vf//2>/5.2F 2’”: Z” V? ' (Va: A0 Micki/4N7) A” < A” I/vfiwfidv WI > 9’91 A E ops”) 1L9 Mm 52K #1, a 3 W, (e) How man normal modes do each of the following molecules have, C02, 02, H28? _ , C02 “’3 '. 7"" 02 "W #23 " m‘m 372-5? 715’s? 892*5-"5-“5‘V fire-"$19 3 (f) Consider vibration—rotational spectra for a heteronuclear diatomic molecule. Stretch the 5% : expectedspectrum for all transitions between v=0 and v=l including J levels from 1:0 through :3 for each. Label the R branch and the P branch. A 75/ . mt! ATE”) fifit (g) What condition must arrfiflecule meet in order to have Raman—active modes?' h , 77m Ma Q W e W a“) 13% W )5 W C kiwi-97%) M m Meme, ' KEY Draw electronic band structure energy diagrams to explain the defining characteristics of (5%. conductors (metals), insulators, and semiconductors. Be sure to label the vacuum level, the conduction band, the band gap (where appropriate), and the valence band. /\ WWW/1 flat/£1 \\ Problem #5 (worth 15 %) end of exam Problem # 1 (worth ID % credit) (a) What is the difference between galvanic and electrolytic cells? (b) Two electrolytic cells were placed in series. One contained a solution of AgN03 and the other a solution of CuSO4. Electricity was passed through the cells until 1.273 gm. of Ag had been deposited. How much copper was deposited at the same time? The amounts of the two elements deposited would be in direct proportion to their gram-equivalent weights. T herefore:, 51-" 1.273 g. Ag = 107.88 g. Ag :c g. Cu 31.77 g. Cu or x = 0.3749 g. of Cu deposited. (c) How many grams each of Ag+ and Cu+2 ions would be deposited by 0.040 Faraday? eposits one gram-equivalent weight 01 an Since one faraday d I I gram-equlvalent weight element, then 0.040 faraday would deposit 0.040 of an element. Therefore: . . 107.88 X 0.040 = 4.3 g. of Ag deposited and I 31.77 X 0.040 = 1.3 g. of Cu deposited. Problem # 2 (worth % credit) (a) Con51de1 the overal‘lereacnon ZNOZ + F2 > ZNOzF, With the proposed mechanism ' 4 ( [00,; N '> 1) N02 + F27: N02F + F Cr” Exrn give/ll, 2) F + N02 —’-'s N021: 1—2 What is the relationship between the eq ' , , rate constants in the mechanistic steps? Show your work. What is the basis what :Law") for l ' l > he finding this realtionship? 1} Wain, I 7, small-'53 = £./C’V”>f3e[FJe g Ki : Ova/79’ : 1,1; M lac/11 0/in “ML K We 17;, (b) Use the Rate Limiting Step Approximation to get the Differential Rate Law for this reaction. 1 CM)»: W rm 5‘ - /2 4’3???" Qt. Du“? > fly A: I) .. cm“? s Laval/5.7 at g 1) id: __ 1/2 MNM- /, mang ,4‘ (c) Use the Steady State Approximation to get the Differential rate Law for this reaction. 0M 1143 “ ’ 92 W 0mm _ la [,6 [EA/02102 J + A [MflEFJj f. ,3» 72‘? fiTQAC/IM7E l we] "" » [N92] 44, CN023C53 : I; [F] I— 4:6ng r MAC/vomnzgn KW {Milt} = A, [WHEEL We 3/4/98! 1a Consider the potential energy curves for the diatomic molecule, AB, and its cation, AB+ shown below. This question deals with dissociation energies, Do; equilibrium bond lengths, Re; and ionization energies, IP. Your answers must be in terms of these quantities. Problem # 3 (worth [5% of the grade on this exam) \tw ~r~ - — ..’,5=- , ox, ,9. ,P-,..,.- e I‘ -’ , On the diagram above, indicate, like so f , answers to the following. 1703) l (a) the energy difference between the atomic asymptotes, (b) the energy difference between v=0 of AB and v=0 of AB+, (c) the dissociation energy of AB, i.e., DO(AB), and (d) the dissociation energy of AB“, i.e., D0(AB+). (e) Write an equation indicating the energetic relationship between D0(AB) and D0(AB+). IP04!) + 900%”) = M!) r .276?) 0k I], 641?) —~ Dom") = How —— I/M) (0 Which has the greater Re, AB«01(circle one)? Indicate the location 'of both Re(AB) and Re(AB+) on the above diagram. (g) Which has the greater bond strength,r AB+(circle one)? How do you know? am) > Ms") [(5 / Look at the periodic table attached to the back of this exam. Consider the first row of transition metal atoms, i.e., Sc through Zn. Using your knowledge of the electronic structure of atoms (their electronic configurations) and the organization of the periodic table, which of these 10 atoms should you expect to be paramagnetic and which should you expect to be diamagnetic? MMMWWi/b M Problem # 4 (worth [0 %) Problem # 5 “(worth 5 %) (a) What should you expect the geometric structure of phosphine, PH3, to be? If there are distortions from high symmetry geometries involved, be careful describe them fully via a picture and/or words. r . Laue fflzfi O\> [07° N N [(713 L‘e I) P fl [7; I f (b) What should you expect the geometric structure of silane, SiH4, to be? 1% 6/7?! /e. ,4 T672A/i/eflf0/w ( la (a) Given your knowledge ctronegativities and chemical bonding, which should have a Problem #6 (worth %) bigger dipole moment, HF o circle one). Explain why. AM o raw/cg xvi/‘2” 2.7 MM ,9 twat; CA‘AMe &e/A,PA774A/ 724M flag? #4 (b) Draw the structure of a water molecule and show the partial charge distribution that gives water its dipole moment. Indicate the axis of its dipole moment vector by drawing a line through the molecule. (You don't need to indicate the direction of its dipole moment.) 6‘. / \ 51* H + W 6‘ 7" (c) What is the dipole moment of benzene? m 262,80 ((1) The molecular ion, N 0+, is isoelectronic with what molecule? (e) The noble gases are inert to chemical reaction except under rather extreme conditions. So, for example, argon is almost always inert to reaction. Should you therefore expect Art to be inert or chemically reactive? Why? _\ RAW 11/ e. m” swarm/z» rmcmee [a dire 775547 {1;— (3L (W442) wfi’z‘cfil I'J’ flacfiye fifwwt )3 AN 0 Meg 4724, (f) Cs+ should be expected to act chemically like which e ement? Xe (g) The second column (Group) of elements from the left side on the eriodic ta 1e be ins with ' Be. What is this family of elements called? AAMLM: flfifl (202 AM/ [(53 What is characteristic about the valence electronic configuration of this Group? 3’— What is the electronic configuration of Ba? (You can use inert gas/closed shell short—hand as part of your answer.) [J 9. Which atom has the larger radius, Sr ocircle one)? Why? [713’ A» Peg/we 72w) 77/47 Mar? Arm fler Mm A? fin de , Pawn: A ‘CoAq/W _ _ E (h) What IS the most electroneganve atom 1n the penodic table? . Problem # 7 (worth 5 %) / Sizes of things (multiple choice) Circle one (a) Typical chemical bond lengths are nearest to (1) 0.1 A) 10 A, (4) 100 A, or (S) 1 nm (where A 2: Angstroms and nm =nanometers)? - ngths of visibl light are nearest to (1) 30 times, (2) 0.01 times, (3) the same as, (5) 2,000 times or (6) 11,000 times larger than the physical size of a typical small (c) The bond strength of H2 is nearest to l) 100 kcal/mol (2) 2,000 kJ/mole, (3)200 kcal/mole, (4) 2 eV, (5) 200 kJ/mole, or (6) 10 kcal/mo - (d) The bond order of carbon—carbon bonds in benzene is (1) 0, (2) l, 4) 2, (5) 5/2, or (6) 3? (e) The energy of e - ~ transitions in molecules are typically nearest to (1) 12 eV, (2) 1 eV, (3) 100 kcal/mole, t 5) 80 eV, or (6) 50 eV? (f) The energy of nuclear transitions are typically nearest to (2) 103 eV, (3) 10'1 eV, (4) 20,000 kcal/mole, or (5) 100 MeV? v Problem # 8 (worth 5 % credit) Complete. the following nuclear reactions: l (a) 7N14+2He4 --> 3017 + 1H ? ftofi/V 0 (b) 1H3 —-> 2He3+ :19? eLecfloN HI (C) IINEI23 +2He4 ~> 12Mg26 + _l___? [2070” l (d) 21H2 —-> 2H63 + on 7 New/TIN y (e) Reaction ((1) above is an example of what kind of nuclear process? ’0 ’r Problem # 9 (worth % credit) (a) Draw the molecular orbital correlation diagram for the molecular anion, Molecular orbitals g N 05p: > 0 Atomic orbitals Atomic orbitals (Atom A) l/ M \ I W —\\\ (Atom B) moot \\ . \\\ ‘Qly—2p \‘ I” /II \\ Jr II L-w'N N lr—Kly—K / 02‘ \ (b) Write out its electronic configuration. (025)2(o;)2(mafiazpfwrp)’ (c) Is NO paramagnetic? Is NO' diamagnetic? Why? fl LE; a9 Jfi/ (a) Consider a particle in a one—dimensional box. If its width, L, is such that its n=2 --> n=1 transition emits radiation having a frequency of 1015 see1 (that's visible light), how much bigger (that is, wider) will this box (with the same particle in it) have to be expanded in order for the same transition to emit radiation at the frequency of an AM radio (106 secrl)? Problem # 10 (worth % credit) 2 L 31" 3 m z _ E / #5 Aéa—wr/ W 5M5 9’ 45: Ar 4? 3442 I: 2. 9 W '12:.- % Iotlowg '7‘ M106 - Li {L 7;]?— 3.3x10 L; I I!) '/ (b) Draw an energy level diagram for the hydrogen atom Ishowing the energies (not the wavefunctions) of all allowed orbitals (states) from n=l through n=3. Label all of them with their quantum numbers (n, 1, m1, but not ms). as well as their orbital ( ., 23) designations. a we! or: EQuMLeNT r. [0 *l '2 1w 1,19,24,44) .eaz. (ma 2, , ; J 59"} 71:3 ,t= IO 33 3 . 3d ,4 3 3d a” M ’50 L" < 2 ugh/my] a -/) I, 2 (c) If V represents a normalized wavefunction, evaluate the integral, SWHWd’t, where dt is a volume element and the integration is carried out over all space. . i by (A M r :W «Wm WM WE?" , 3 I 3»; fir/m = 5‘ PE/W : 15W: E ...
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chem04 - W (a) Construct the molecular orbital energy level...

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