SOME TOUGH COLLEGE PROBLEMS! .. : 4. How many electrons should be shown in the Lewis dot structure for carbon monoxide? N O O

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1 SME TUGH CLLEGE PRBLEMS! LEWIS DT STRUCTURES 1. An acceptable Lewis dot structure for 2 is (A) (B) (C) 2. Which molecule contains one unshared pair of valence electrons? (A) H 2 (B) H 3 (C) CH 4 acl 3. The most reasonable Lewis structure for Cl is Cl Cl (E) Cl (A) Cl (B) Cl (C) 4. How many electrons should be shown in the Lewis dot structure for carbon monoxide? (A) 8 (B) 14 (C) The Lewis structure of 2 + is best drawn as + (E) + (A) (B) (C) (E) Which has a Lewis dot structure with the greatest number of unshared pairs on the central atom? (A) H 3 (B) IF 3 (C) SeCl 2 ICl 2 7. Which molecule contains only two unshared pairs of electrons? (A) H 2 (B) H 3 (C) BeCl 2 Mg 1

2 8. Which of the following molecules would have a trigonal planar molecular arrangement? (A) CBr 4 (B) BF 3 (C) F 2 PCl 3 (E) AsF 5 9. In the Lewis structure of SF 2, there are single bonds and total lone pairs? (A) 2,8 (B) 3,8 (C) 2,2 2,6 (E) 3,6 10. Which of the following species is ICRRECTLY matched with the number of lone pairs found on the central atom? (A) S (B) 3 1 (C) XeF 2 3 S 2 1 (E) IF Which of the following molecules violates the octet rule? (A) CBr 4 (B) F 3 (C) F 2 PCl 3 (E) AsF Which of these contains at least one multiple bond? (A) 3 (B) PH 3 (C) 2 H 4 SiCl 4 (E) BH Sulfur dioxide can be described by the structures below. This implies that S S (A) The two bonds in S 2 are of equal length, and the electronic distribution in the two S bonds is identical. (B) The single bond is longer than the double bond and the electronic distribution in the two S bonds is different. (C) An electron pair in the S 2 molecule alternates back and forth between the two sulfur oxygen electron pairs so that the two different bonds seem to exchange positions. The S 2 molecule revolves so that the two different bonds seem to exchange positions. 14. How many different resonance forms are possible for the oxalate anion, C 2 2 4? (A) 3 (B) 7 (C) 6 1 (E) Which molecule exhibits resonance? (A) 3 (B) BeCl 2 (C) C 2 H 2 Se (E) F What are the formal charges on the boron and nitrogen in the compound BF 3 H 3? (A) 2 and +2 (B) +2 and 2 (C) 0 and 0 +1 and 1 (E) 1 and +1 2

3 17. The structure of the C 3 2 ion can be described by these Lewis structures which means that (A) (B) (C) C C two C bonds are single bonds, the third C bond is a double bond. three independent forms of the C 2 3 ion coexist in equilibrium. the electrons must be rapidly exchanging among the three forms. the C 2 3 ion exists in only one form which is a composite or average of the three principal structures shown. C 18. Which is the least significant contributing structure to the resonance hybrid of the nitrate ion? (A) (B) (C) 19. What are the formal charges on each of the atoms in the PH + 4 ion? (A) P = 0; H = ¼+ (B) P = 0, H = 0 (C) P = 4+; H = 1 P=1+; H=0 (E)P=0; H= What is the formal charge on the sulfur atom in the sulfate anion (S 2 4 )? (A) 2 (B) 0 (C) 2 4 (E) 6 3

4 21. What is the formal charge on the nitrogen atom in the nitrate anion? (A) 2 (B) 1 (C) 0 +1 (E) +2 EERGY I VS. EERGY UT 22. Given the bond energies (in kj/mol) below, calculate the energy change (in kj) for C(g) + H 2 (g) + F 2 (g) CH 2 F 2 (g). Is this a spontaneous process meaning, is it going to occur easily without much effort? C H 414 C F 486 H H 435 F F 159 H F 569 (A) ΔH = +900 (C) ΔH = 900 (B) ΔH = 465 ΔH = Calculate energy change for H 3 (g) + Cl 2 (g) H 2 Cl(g) + HCl(g) using the bond energies H 389 Cl Cl 243 H Cl 431 Cl 201. Is this a spontaneous process meaning, is it going to occur easily without much effort? (A) 337 kj (B) +337 kj (C) 84 kj 0 kj 24. Calculate the energy change for the reaction, C 2 H 4 + H 2 C 2 H 5 H using the following bond energies (in kj/mol). Is this a spontaneous process meaning, is it going to occur easily without much effort? CH 413 C 358 CC 347 H 467 HH 432 C=C 614 C= 799 (A) 37 (B) +179 (C) (E) Using the bond energies given, estimate the energy change for making carbonic acid (H 2 C 3 ) from C 2 and H 2. Is this a spontaneous process meaning, is it going to occur easily without much effort? CH 413 C 358 CC 347 H 467 C= 799 C 1070 (A) +493 kj/mol (B) 493 kj/mol (C) +83 kj/mol +799 kj/mol (E) 467 kj/mol ELECTREGATIVITY AD BD PLARITY 26. Which would be expected to be the most electronegative? (A) P (B) As (C) Si Al 27. The element with the greatest tendency to gain electrons is (A) F (B) At (C) (E) Bi 28. Which atom has the highest electronegativity? (A) Br (B) Mg (C) C 4

5 29. Which of these elements should be the most active as a nonmetal, given that their electronegativity values are Q 0.9 R 1.0 T 2.8 X 3.0 Z 4.0 (A) Q (B) R (C) T X (E) Z 30. Which of the following statements about electronegativity (E) is FALSE? (A) (B) (C) onmetals usually have higher E than metals Electronegativities can be directly measured experimentally HCl has a higher partial ionic character than HI because the E of Cl > E of I In general, an atom s E is inversely related to its radius 31. In which bond are the partial charges on the atoms correct? (A) δ+ Si δ (B) δ+ ClBr δ (C) δ+ B δ δ+ ClCl δ 32. Which of the following compounds contains the LEAST polar bonds? Atoms H S P As Cl Si Sb Electronegativity (A) PH 3 (B) AsCl 3 (C) SiH 4 SbCl 3 (E) H 2 S 33. Which set of bonds is arranged in order of increasing polarity? (A) SiS < Si < SiP < SiF (B) Si < SiF < SiS < SiP (C) SiF < SiS < Si < SiP SiP < SiS < Si < SiF 34. The BrCl molecule may be represented by the formula BrCl. The polarity is best represented as (A) Br δ+ Cl δ+ (B) Br δ Cl δ+ (C) Br δ Cl δ Br δ+ Cl δ IIC BDIG 35. The lattice energy for ionic crystals increases as the charge on the ions and the size of the ions? (A) increases, increases (B) increases, decreases (C) decreases, increases decreases, decreases 36. Select the compound with the highest (most negative) lattice energy? (A) CaS (B) Mg (C) ai LiBr 37. Select the compound with the lowest (least negative) lattice energy? (A) CsBr (B) acl (C) Sr Ca 5

6 38. Calculate the lattice energy for LiBr(s) given the following information Li(s) Li(g), ΔH = +166 kj/mol ΔH f (LiBr) = 351 kj/mol Br 2 (l) 2 Br(g), ΔH = +194 kj/mol EA of Br(g) = 325 kj/mol IE of Li(g) = kj/mol (A) 906 (B) 1575 (C) (E) Use a BornHaber cycle based on the formation of Mg to determine heat released for the process, (g) + 2e 2 (g) in kj/mol Mg(s) Mg(g) ΔH = +150 kj/mol ΔH f (Mg) = 602 kj/mol Lattice energy of Mg(s) = 3920 kj/mol IE1 + IE2 Mg = kj/mol Bond energy of = = 498 kj/mol (A) 1314 (B) +739 (C) (E) Calculate the lattice energy of magnesium sulfide given that (in kj/mol) Mg(s) Mg(g) ΔH = 153 IE(1) Mg, IE(2) Mg ΔH = 700, 1480 ΔH f (MgS) ΔH = 343 S 8 (s) 8S(g) ΔH = 4460 EA(1) S, EA(2) S ΔH = 100, 203 (A) 6833 kj/mol (B) 2930 kj/mol (C) 2244 kj/mol 6147 kj/mol 41. Calculate the electron affinity of chlorine from the following data (in kj/mol) Rb(s) Rb(g) ΔH = 85.8 IE (Rb) ΔH = diss E. (Cl 2 ) ΔH =226 ΔH(latt)(RbCl) ΔH = 695 ΔH f (RbCl) ΔH = 431 (A) 530 kj/mol (B) 445 kj/mol (C) 417 kj/mol 332 kj/mol VSEPR 42. Which pair is geometrically similar? (A) S 2 and C 2 (B) C 2 and F 2 (C) PH 3 and BF 3 S 2 and The structure for SeF 3+ is (A) trigonal pyramidal. (B) square planar. (C) tetrahedral. rectangular planar. 44. The molecular structure of BrF 5 is (A) square pyramidal. (B) trigonal pyramidal. (C) trigonal bipyramidal. octahedral. 45. Which is planar? (A) H 3 (B) S 2 3 (C) C 2 3 H 3 + 6

7 46. Which molecule is linear? (A) H 2 (B) H 3 (C) 2 C 2 (E) H 2 S 47. A molecule consists of four bonding pairs of electrons and no lone pairs. What is its structure? (A) square planar (B) tetrahedral (C) linear square pyramidal 48. Which statement is true of methane? (A) It is a tetrahedral molecule. (B) It contains single and double bonds. (C) It has extremely strong chemical bonds It does not occur in nature. 49. H 3 (pyramidal geometry) reacts with BF 3 (planar geometry) to form the addition compound, H 3 BF 3. What is the geometry around the nitrogen and boron centers in the addition compound? (A) Both centers are tetrahedral. (B) itrogen tetrahedral and boron linear. (C) itrogen pyramidal and boron planar. itrogen planar and boron pyramidal. 50. Which of the following molecules does T possess a trigonal pyramidal molecular shape? (A) H 3 (B) CCl 2 (C) H 3 + Cl 3 (E) PFCl Which of these molecules or ions has a square planar structure? (A) SiBr 4 (B) H 4 + (C) Cl 4 XeF According to VSEPR theory, the III bond in I 3 is expected to be (A) 180 (B) 270 (C) (E) Predict the real bond angles in BrF 3 using the VSEPR theory (A) more than 120 (B) between 109 and 120 (C) between 90 and 109 less than Predict the real bond angles in SeCl 2 using the VSEPR theory (A) more than 120 (B) between 109 and 120 (C) between 90 and Which is the largest bond angle? (A) angle S in S 2 4 (B) angle Cl C Cl in HCCl 3 (C) angle F Be F in BeF 2 angle H H in H Which compound would be expected to have the largest dipole moment? (A) C 2 (B) BF 3 (C) S 2 CF 4 7

8 57. Which molecule is polar? (A) BF 3 (B) C 2 (C) CF 4 H 2 S 58. The bond type and molecular polarity of SiCl 4 are Bond Type Polarity of Molecule Bond Type Polarity of Molecule (A) polar nonpolar (B) polar polar (C) nonpolar polar nonpolar nonpolar 59. Which molecule is nonpolar? (A) CCl 4 (B) HCl (C) CF 3 Cl CHCl 3 (E) H Experiment shows that the molecule H 2 Se has a dipole moment. Which statement MUST therefore be incorrect? (A) The H 2 Se molecule is linear. (B) The H 2 Se molecule is covalent. (C) The H 2 Se molecule is electrically neutral. There must be a difference in electronegativity between hydrogen and selenium. 61. Which of the following possesses polar bonds but has no molecular charge? (A) BF 3 (B) 2 (C) CHCl 3 PF 3 (E) Cl f the molecules C 2, H 3, H 2 and CH 4, which are polar? (A) C 2, H 3 and H 2 (B) H 3, H 2 and CH 4 (C) C 2 and CH 4 (B) C 2 and H 3 (E) H 3 and H Which of the following has a net dipole moment? (A) BeCl 2 (B) SF 2 (C) KrF 2 C Which of the following has no molecular charge? (A) CS 2 (B) H 2 S (C) CH 2 Cl 2 PH 3 (E) CH 2 GEERAL STUFF 65. Which one of the following properties is least characteristic of substances composed of small, covalentlybonded molecules? (A) low melting point (B) low boiling point (C) weak bonds poor electrical conductor when solid (E) poor electrical conductor when molten 8

9 66. Which of the following properties is least characteristic of metals? (A) high melting point (B) high boiling point (C) brittleness good electrical conductor when solid (E) good electrical conductor when molten 67. Which of the following properties is least characteristic of ionic compounds? (A) high melting point (B) high boiling point (C) brittleness poor electrical conductor when solid (E) poor electrical conductor when molten ASWERS D B C C C D A B A B E A A E A E D A D C D D D A C A A D E B A A D D B B A D B B D D A A C D B A A B D A D C C C D A A A A E B A C C E 9