CHM2045 S13: Exam # MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

Transcription

1 CHM2045 S13: Exam # MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) How would replacing one of benzene's C atoms and the H atom attached to it with an N atom (C5H5N) affect the delocalized electrons? A) There would be no delocalized electrons but a double bond between the N and a C. B) Only the five C atoms would be included in the delocalized electrons. C) The N can have delocalized electrons like C. D) The molecule would not be stable. E) There would be no delocalized electrons but a double bond between the N and the C on each side of the N. 2) Electrostatic potential maps use color to portray the calculated electron distribution in a molecule. Atoms that are electron poor and carry a!+ charge are shown in blue. Atoms that are electron rich and carry a!- charge are shown in red. Atoms with little or no charge are shown in green. The electrostatic potential map of CH 3 Cl below should show A) C red and Cl blue. B) C blue and Cl red. C) C green and Cl blue. D) C blue and Cl green. 3) What is the correct formula for the product of the reaction of strontium metal and nitrogen? A) Sr2N3 B) SrN3 C) Sr3N2 D) SrN2 E) SrN 4) Which combination of hybrid orbital descriptions and electronic geometry descriptions is INCORRECT? A) sp2/trigonal planar B) sp3d/square planar C) sp3d2/octahedral D) sp/linear E) sp3/tetrahedral 5) The sp 3 d 2 atomic hybrid orbital set accommodates electron domains. A) 2 B) 3 C) 4 D) 5 E) 6 6) The hybridizations of nitrogen in NF3 and NH3 are and, respectively. A) sp 2, sp 2 B) sp 3, sp 3 C) sp, sp 3 D) sp 2, sp 3 E) sp 3, sp A-3

2 7) Which atom can accommodate an octet of electrons, but doesn't necessarily have to accommodate an octet? A) N B) C C) O D) B E) H 8) Of the atoms below, is the most electronegative. A) Cl B) Ca C) Si D) Rb E) S 9) Why don't we draw double bonds between the Be atom and the Cl atoms in BeCl2? A) That would result in more than eight electrons around each chlorine atom. B) That would result in the formal charges not adding up to zero. C) There aren't enough electrons. D) That would result in more than eight electrons around beryllium. E) That would give positive formal charges to the chlorine atoms and a negative formal charge to the beryllium atom. 10) The carbon-carbon " bond in ethylene, H 2 C CH2, results from the overlap of. A) sp hybrid orbitals B) s atomic orbitals C) sp 2 hybrid orbitals D) sp 3 hybrid orbitals E) p atomic orbitals 11) Assuming molecular orbital diagrams similar to that of O2, use MO theory to predict the proper ordering of bond energies of the following pairs. A) B) C) D) 12) The electron domain and molecular geometry of BrO 2 - is. A) trigonal planar, trigonal planar B) tetrahedral, trigonal planar C) trigonal pyramidal, linear D) tetrahedral, bent E) trigonal pyramidal, seesaw A-4

3 13) Draw the Lewis structure for NO 2 including any valid resonance structures. Which of the following statements is TRUE? A) The nitrite ion contains two N O bonds that are equivalent to bonds. B) The nitrite ion contains two N O double bonds. C) The nitrite ion contains one N O single bond and one N O double bond. D) The nitrite ion contains two N O single bonds. E) None of the above are true. 14) The electron-domain geometry and the molecular geometry of a molecule of the general formula ABn will always be the same if. A) n is less than four B) there is more than one central atom C) n is than four D) there are no lone pairs on the central atom E) the octet rule is obeyed 15) Arrange the following bond in order of bond polarity.: Cs-F, H-Cl, F-F, H-F, and C-H. A) Cs-F < F-F < H-F < H-Cl < C-H B) F-F < H-Cl < Cs-F < C-H < H-F C) C-H < F-F < H-F < H-Cl < Cs-F D) F-F < C-H < H-Cl < H-F < Cs-F E) H-F < Cs-F < F-F < C-H < H-Cl 16) Based on molecular orbital theory, the only molecule in the list below that has unpaired electrons is... A) N2 B) Li2 C) C2 D) F2 E) O2 17) How many of the following molecules would be expected to have # > 0 (i.e., have a nonzero permanent dipole moment)? CH 4 H 2 O CHCl 3 Benzene (C 6 H 6 ) CH 3 F A) 0 B) 1 C) 2 D) 3 E) 4 18) Which of the following compounds would be impossible according to the Lewis model? A) CF 4 B) H 2 F C) SF 6 D) BF 3 E) H 3 O + 19) What is the formal charge on the chlorine atom in the best Lewis structure of perchlorate, ClO 4 -? A) +3 B) +2 C) +1 D) 0 E) -1 20) Of the bonds C-N, C N, and C N, the C-N bond is. A) intermediate in both strength and length B) strongest/shortest C) strongest/longest D) weakest/shortest E) weakest/longest A-5

4 The diagram below is the Born-Haber cycle for the formation of crystalline potassium fluoride. 21) Which energy change corresponds to the lattice energy? A) 6 B) 4 C) 3 D) 2 E) 5 22) The bond length in an HI molecule is 161 pm and the measured dipole moment is 0.44 D. What is the percent ionic character of the H-I bond in HI? (Hint: # = 4.80D for two univalent ions separated by 100 pm.) A) 27% B) 54% C) 9.2% D) 73% E) 100% 23) Acetylene combines with hydrogen to form ethane (C 2 H 2 + 2H 2 C 2 H 6 ). Given the following bond energies (in kj/mol), calculate the energy change for this reaction. H-H (436) C-H (414) C-C (347) C=C (611) C C (837) A) -520 kj B) +122 kj C) -294 kj D) +520 kj E) -122 kj 24) In comparing the same two atoms bonded together, the the bond order, the the bond length, and the the bond energy. A) smaller,, B), shorter, C),, smaller D),, E), longer, 25) The Lewis structure of N2H2 shows. A) each nitrogen has two nonbonding electron pairs B) a nitrogen-nitrogen single bond C) each nitrogen has one nonbonding electron pair D) a nitrogen-nitrogen triple bond E) each hydrogen has one nonbonding electron pair 26) The central Xe atom in the XeF 4 molecule has unbonded electron pairs and bonded electron pairs in its valence shell. A) 4, 0 B) 4, 2 C) 1, 4 D) 2, 4 E) 4, 1 A-6

5 27) The structure of aspirin is given below. What is the O-C-C bond angle, "x", in aspirin? A) ~180 B) ~109 C) ~90 D) ~120 A-7

6 Answer Key Testname: CHM2045 S13 EXAM 2-3 1) C 2) B 3) C 4) B 5) E 6) B 7) D 8) A 9) E 10) C 11) A 12) D 13) A 14) D 15) D 16) E 17) D 18) B 19) C 20) E 21) E 22) A 23) C 24) B 25) C 26) D 27) D A-8