2011 Exam 2 Crib

2011 Exam 2 Crib - Chemistry 24101 Spring 201 1 Exam 2 Name...

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Unformatted text preview: Chemistry 24101 Spring 201 1 Exam 2 Name \ TA Section 1. You are responsible for all information on this page. 2. Show all work on the exam, and write answers in ink. Cleariy indicate your answer and mark through any writing that should be ignored in grading. 3. There are four questions and a bonus. You should also have a Periodic Table. Potentially Useful Information cubic closest packing Radius Ratio Rules r+/r' (minimum) Lattice Nam 1 g = 6.022 x 1023 amu 1A=10'3cm 1 pm = 10'12 m 1. (20 points) The Figure below depicts a partial MO scheme for the diatomic molecule TiO. For simplicity it includes only the 3d atomic orbitals of titanium and the 2p atomic orbitals of oxygen. The scheme incorporates all valence electrons of titanium, but it omits the 23 valence orbital and electrons of oxygen. Di 2kg?— . 2 ’,,.——G 16‘ '- é S *fii'hl‘bz' Jig)?“ Tr ~53 I (9% . \ . . .\ l \ \ \ \ h . . \ , L 1’ . “the A. Find and label any (all) missing MO('s) generated by the AO’s used. Explain your reasoning, and indicate where it (they) fits (fit) in the diagram. Then fill the occupied MO’s with electrons as appropriate, and predict the net bond order, i. e., single, double, or 2.5, etc. 2,2 gikxe, E (inks \ OW. Sn $2153 a Cfimi'h 9314.13 ggdhims 8‘ 21.3% Zf’thl B. Define a convenient axis system with the z-direction as the internuclear axis. Then sketch a contour of the 10 MO indicated in the diagram, and shade the lobe(s) as appropriate. Indicate the constituent AO('s). Does oxygen or titanium play a bigger role in the mixture? Explain your reasoning. . f 2. 9 f a I): l ; 30L} 01(01ng Ms ct luau, WEE-YET» . l i . ‘ bk 3 41‘ [SW 14 T? O T; 3J5 C. Keep the same axis convention as in B, and sketch a contour of the non-bonding MO('s). (View down the axis of your choosing.) Identifl the constituent AO('s). “S ++++ Energy 2. (20 points) Assume that the diamond structure of C(s) amounts to a variation of the zinc-blende lattice with carbon atoms residing in the Zn2+ and 82' positions. (If you cannot visualize the diamond structure, answer the following questions for a lattice containing NaCl(s) and use the same edge length in C for partial credit.) A. Sketch the unit cell of C(s) diamond based on the closest packing diagram found in Useful Information. CL» afloltfi’v-likfilfilga] ‘ MA 4‘ batten ‘0‘ )ZCLJQ “I L.) singi.tifituiitfimfi V014. B. Pick a carbon atom in your diagram and show the number of nearest neighbors. (N14 C. Show your work. (Atomic mass: C 12.01g/m01e.) m-t €0in gc swim (Exitol _, 3. ‘ Quinn”) (3?! X10“ If the unit cell in A has an edge length of a = 357 pm, estimate the density of C(s) diamond. D. Finally, estimate the covalent bond radius (1/2 C-C distance) in pm. Note: The face and body diagonals of a cube have lengths 2”2 length. C4: 1: Ed a and W .— 8 ‘- l‘czé’g‘o‘ ' 3 W a, respectively, where a is the edge (zsfl : pm 3. (20 points) Assume that a simple MO diagram describes the valence orbitals of boron monoxide BO for which the energy ordering is 16<2G<11t<36<21t<46. A. Write the electronic configuration of B0 (i. e., 1626“. ..), and determine how many unpaired electrons there are in the ground state. q I 3 3ran 6" a: timid-- In?“th m 36’ imwie” B. The following are contours of the 3G MO’s from B0, B2, and 02 in random order. Associate each MO with the correct molecule. Specify all participating AO’s in each MO, and briefly WWI” reasoning. U. I lbttme cad-Ix Bil—Rt 4. (20 Points A and B total) A. The standard heat of formation of barium peroxide (Ba02(s)) can be broken down into a series of steps as a Born-Haber cycle. The cycle of interest contains 6 terms in all and accounts for ionization, electron affinity, atomization, and calculated lattice energy (-U) effects. Only two of the steps are exothermic. In the Figure the blocks on the right designate the exothermic terms, including a dark block on the top right representing a weakly exothermic step. m chemical equations for the two exothermic steps in the process, and identify the process associated with the single most endothermic step (unshaded block). Cum _ a a“ to 0115] is usLASWWL) \ V) M B. Complete ad balance the following reactions. i. CH4(g) + 1.120%) % COu-fi 'l' 3 H2 ’3! . Lf- g i NOR L t- BNQCX ii.. Na 3 3 “h” _ é a H( ) + I BC] fl_—> iii. Hag) + Sts) -“—> Hi2, SUM Bonus (3 points) If one is designing a molecule is to engage in hydrogen bond formation to a polar X-H species, the molecule should contain at least one from a set of what three atoms? 0, U/F SM&)NM{LJWMKSM% ...
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2011 Exam 2 Crib - Chemistry 24101 Spring 201 1 Exam 2 Name...

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