exam 3 chem 141 fall 2015

Chemistry 141 Name Martin Larter Exam 3A November 7. 2015 Multiple Choice (30 points) Page 5 (14 points) Page 6 (21 points) Page 7 (22 points) Page 8 (15 points) Page 9 (12 points) Total (114 points) Chemistry Formulas and Constants Kinetic energy = ½ mv 2 w = -P  V E = hν Δ x Δmv≥ h 4 π Rate 1 Rate 2 = √ MW 2 MW 1  G o = -nFE o  G = - RTlnK w=dxF E = mc 2 P total = P 1 +P 2 +P 3 +… u = (3RT/MW) ½ H  =E  M 1 V 1 = M 2 V 2 u = (3RT/MW) ½  G =  H - T  S P total = P 1 + P 2 + P 3 + … PV = nRT Rate  (MW) -½ ( P + n 2 a V 2 ) ( V − nb ) = nRT c = λν λ deBroglie = h mv  = iMRT P total = P 1 + P 2 + P 3 + … ln ( [ A ] [ A ] o ) =− kt ln ( k 2 k 1 ) = ( E a R ) [ ( 1 T 1 ) − ( 1 T 2 ) ] E = E o − ( 0.0592 n ) log Q ln ( P 2 P 1 ) = ( ΔH vap R ) [ ( 1 T 1 ) − ( 1 T 2 ) ] ν = c λ 1 λ =− R ( 1 n i 2 − 1 n f 2 ) λ deBroglie = h mv ΔxΔ mv ≥ h 4 π Constants F = 9.65 x 10 4 C h = 6.626 x 10 -34 J sec c= 2.9979 x 10 8 m/sec mass electron = 9.109 x 10 -31 kg R E = 2.18 x 10 -18 J e = 1.602 x 10 -19 C R = 0.0821 L atm/mol K = 62.4 L torr/mol K = 8.31 kJ/mol K 1

Grossmont College Periodic Table IA VIIA NOBLE GASES 1 H 1.008 IIA IIIA IVA VA VIA 1 H 1.008 2 He 4.002 3 Li 6.941 4 Be 9.012 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 9 F 19.00 10 Ne 20.18 11 Na 23.00 12 Mg 24.30 IIIB IVB VB VIB VIIB VIII VIII VIII IB IIB 13 Al 27.00 14 Si 28.09 15 P 30.97 16 S 32.06 17 Cl 35.45 18 Ar 39.95 19 K 39.10 20 Ca 40.08 21 Sc 44.96 22 Ti 47.90 23 V 50.94 24 Cr 52.00 25 Mn 54.94 26 Fe 55.85 27 Co 58.93 28 Ni 58.70 29 Cu 63.55 30 Zn 65.38 31 Ga 69.72 32 Ge 72.59 33 As 74.92 34 Se 78.96 35 Br 79.90 36 Kr 83.80 37 Rb 85.47 38 Sr 87.62 39 Y 88.91 40 Zr 91.22 41 Nb 92.91 42 Mo 95.94 43 Tc (99) 44 Ru 101.1 45 Rh 102.9 46 Pd 106.4 47 Ag 107.9 48 Cd 112.4 49 In 114.8 50 Sn 118.7 51 Sb 121.8 52 Te 127.6 53 I 126.9 54 Xe 131.3 55 Cs 132.9 56 Ba 137.3 57 La 138.9 72 Hf 178.5 73 Ta 180.9 74 W 183.9 75 Re 186.2 76 Os 190.2 77 Ir 192.2 78 Pt 195.1 79 Au 197.0 80 Hg 200.6 81 Tl 204.4 82 Pb 207.2 83 Bi 209.0 84 Po (209) 85 At (210) 86 Rn (222) 87 Fr (223) 88 Ra 226.0 89 Ac 227.0 104 Rf (261) 105 Db (262) 106 Sg (263) 107 Bh (262) 108 Hs (265) 109 Mt (266) 110 ?? (269) 58 Ce 140.1 59 Pr 140.9 60 Nd 144.2 61 Pm (147) 62 Sm 150.4 63 Eu 152.0 64 Gd 157.3 65 Tb 158.9 66 Dy 162.5 67 Ho 164.9 68 Er 167.3 69 Tm 168.9 70 Yb 173.0 71 Lu 175.0 90 Th 232.0 91 Pa 231.0 92 U 238.0 93 Np (237) 94 Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (260) Lanthanide series 2

Multiple Choice (30 points) 1. Which statement is always true according to VSEPR theory? a. The shape of a molecule is determined by the polarity of its bonds. b. The shape of a molecule is determined by the repulsions among all electron groups on the central atom (or interior atoms if there is more than one). c. The shape of a molecule is determined only by repulsions among nonbonding electron groups. d. The shape of a molecule is determined only be repulsions among bonding electron groups. e. none of the above 2. Arrange the ions P 3- , S 2- , Ca 2+ , K + , and Cl - in order of increasing ionic radius, starting with the smallest first. a. Ca 2+ , K + , Cl - , S 2- , P 3- b. P 3- , S 2- , Ca 2+ , Cl - , K + c. P 3- , Ca 2+ , S 2- , K + , Cl - d. K + , Ca 2+ , Cl - , S 2- , P 3- e. P 3- , S 2- , Cl - , K + , Ca 2+ 3. Which one of the following ground-state orbital diagrams only violates Hund's rule ? a. b. c. d. e. 4. Which bond should have the longest length? a. N=N b. N-N c. N≡N d. All three bond lengths should be about the same. e. Impossible to determine from the data given 5. Which of these statements correctly describes the use of formal charge in choosing between possible Lewis structures to describe a molecule? I. Formal charge on all the atoms should be zero, or at least the smallest possible value. II. The sum of the formal charges on all the atoms should equal the charge on the molecule or ion. III. The formal charge on an atom is not affected by the electronegativity of the atom. IV. In an anion containing nitrogen and oxygen, the Lewis structures with a negative charge on the nitrogen will contribute the most to the description of the bonding. a. III and IV only b. I and III only c. II and III only d. II and IV only e. I and II only 6. In general, resonance ________ electrons and ________ molecules. a. delocalizes; destabilizes b. delocalizes; stabilizes c. destabilizes; destabilizes d. localizes; stabilizes e. localizes; destabilizes 7. Which type of molecular orbital is used to describe electron density building up above and below the internuclear axis to form a bond? a. π b.  * c.  * d.  e. s 4

8. The reason Fe 3+ has a smaller ionic radius than Fe 2+ is because a. Fe 2+ has a low electron affinity b. n is smaller for Fe 2+ c. Fe 3+ contains more protons d. Fe 3+ has a higher Z eff e. Fe 3+ has a higher ionization energy 9. List the elements Cs, Ca, Ne, Na, Ar in order of increasing first ionization energy. a. Ne > Na > Cs > Ca > Ar b. Ne > Ar > Na > Cs > Ca c. Ar > Ca > Cs > Na > Ne d. Ne > Ar > Ca > Na > Cs e. None of the above 10. Which of the following atoms is diamagnetic? a. B b. Mg c. C d. Na e. O 11. The greater the electronegativity difference between two bonded atoms, the a. Greater the bond order. b. Greater the ionic character of the bond. c. More unstable the bond. d. Greater the covalent character of the bond. e. None of the above 12. Which reaction below represents the second electron affinity of S? a. S 2 ⁻ (g) → S ⁻ (g) + e ⁻ b. S(g) + e ⁻ → S ⁻ (g) c. S ⁻ (g) + e ⁻ → S 2 ⁻ (g) d. S(g) → S ⁺ (g) + e ⁻ e. S ⁻ (g) → S(g) + e ⁻ 13. Based on the indicated electronegativity’s, arrange the following in order of increasing ionic character: CsBr, LaBr 3 , PBr 3 , MgBr 2 . a. CsBr, LaBr 3 , MgBr 2 , PBr 3 b. CsBr, MgBr 2 , PBr 3 , LaBr 3 c. PBr 3 , MgBr 2 , LaBr 3 , CsBr d. PBr 3 , LaBr 3 , MgBr 2 , CsBr e. Not enough information provided 14. Which of the following is not true? a. A sp 3 hybrid orbital may form a sigma bond by overlap with an orbital on another atom. b. A sp 3 hybrid orbital may hold a lone pair of electrons. c. A sp 3 hybrid orbital may form a pi bond by overlap with an orbital on another atom. d. The sp 3 hybrid orbitals are degenerate. e. All of the above are true. 15. A molecule containing a central atom with sp 3 d 2 hybridization has a(n) ________ electron geometry. a. tetrahedral b. bent c. trigonal bipyramidal d. square planar e. octahedral Problems and short answer 5 element electronegativity Br 2.8 P 2.1 Mg 1.2 La 1.0 Cs 0.7

5. (18 points) Write the best Lewis Electron Dot Structures for the following molecules or ions (Central atom is listed first). Tell the orbital and molecular geometry for each molecule/ion. Show formal charges for all non-zero charges. If resonance structures exist, show them. NS 2 Cl orbital geometry_________________ molecular geometry_______________ Bond angle________________ Hybridization ______________ Polar or Nonpolar_______________ SeOF 2 orbital geometry_________________ molecular geometry_______________ Bond angle________________ Hybridization ______________ Polar or Nonpolar_______________ XeF 2 orbital geometry_________________ molecular geometry_______________ Bond angle________________ Hybridization ______________ Polar or Nonpolar_______________ 6. (4 points) Compare and contrast valence bond theory and molecular orbital theory. 7

7. (15 points) Some species with two oxygen atoms only are the oxygen molecule, O 2 , the peroxide ion, O 2 -2 , the superoxide ion, O 2 -1 , and the dioxgenyl ion, O 2 +1 . Draw an MO diagram for each, on the following page and answer the questions. Note that each box is labeled with a particular species. a. Rank these species in order of decreasing bond length b. Rank these species in order of decreasing bond strength c. Give the bond order in all species O 2 _______________________ O 2 -2 _______________________ O 2 -1 _______________________ O 2 +1 _______________________ d. Identify each species as diamagnetic or paramagnetic O 2 _______________________ O 2 -2 _______________________ O 2 -1 _______________________ O 2 +1 _______________________ e. In terms of the molecular orbital model, which species would be the most likely to gain an electron if any: O 2, O 2 -2 , O 2 -1 , O 2 +1 . Rationalize your answer. 8

10 Molecule/ion_________________________ _____ Molecule/ion______________________ _______ Molecule/ion________________________ ______ Molecule/ion_______________________ _______