CHEM Lab Section Number: Name (printed): Signature: This exam consists of 36 questions all of equal value for a total of 225 points. Make sure that your test has all of the pages. Please read each problem carefully. There are no intentionally misleading questions; each problem should be taken at its face value. Please mark your answers on the Scantron sheet provided to you and on the actual exam. You will be given a periodic table and an exam information sheet to use during the exam. You may remove it from the exam make it more accessible. You may also use the designated Casio fx-300ms-plus calculator or equivalent non-programmable non-graphing scientific calculator during the exam. Use the back pages of the test as scratch paper. You are not allowed to use any devices capable of accessing the internet, textbooks, notes, or homemade reference sheets during the exam. You may leave if you finish the exam early. Give the exam and the information sheet to your TA and leave quietly without disturbing other students. Before leaving, check that all your answers have been properly entered on the Scantron sheet and the exam and that your name is written on every page of the exam and on the Scantron sheet. All cell phones and electronic devices must be turned off and put away. Please remove all hats and caps. Place your books and all papers out of sight under your seat. If the TA believes that you might be looking at your neighbor s paper, you will be asked to move to a new location. Exam scores will be posted on Blackboard as soon as the grading is complete. Your test will be returned to you in the first lab meeting of next week. If you have any questions regarding the grading of your exam, please notify your TA. The time available for the exam is 120 minutes. Good luck! 1 of 10
Name: Lab Section #: Please mark your answers on the scantron sheet using a #2 pencil and also mark your answers on the exam itself. Mark Test From B on your scantron. 1. When a double bond is formed in between two carbon atoms in a ethylene structure, the sigma and pi bond are created by the overlap of and orbitals, separately? (a) sp 3, p (b) sp 2, p (c) sp, p (d) sp, sp (e) sp 2, sp 2 2. What is the hybridization of the central atom in a molecule of H2O? (a) sp (b) sp 2 (c) sp 3 (d) sp 3 d (e) sp 3 d 2 To the right is a molecule of Guanine, one of the main four Nucleobases found in the nucleic acid DNA and RNA. The lone pairs of electrons have been omitted for clarity. Use the structure in answering the following 4 questions. 3. How many lone pairs of electrons are there on a molecule of Guanine? (a) 2 (b) 4 (c) 5 (d) 6 (e) 7 4. How many of the nitrogen atoms in a Guanine molecule have sp 2 hybridization? (a) 0 (b) 1 (c) 2 (d) 3 (e) 4 2 of 10
5. How many pi (π) bonds are there on the molecule of Guanine? (a) 2 (b) 4 (c) 12 (d) 25 (e) 18 6. The carbon on the different molecules can adopt various hybridizations, what is the most common (frequent) hybridization of carbon atoms on Guanine? (a) sp (b) sp 2 (c) sp 3 (d) sp 3 d (e) sp 3 d 2 Use the molecular orbital diagrams below to answer the following 4 questions. 7. Which of the following is the correct electron configuration for C2? (a) σ 1s 2 σ 2s 2 π 2py 2 σ *1s 2 σ *2s 2 π *2py 2 (b) σ 1s 2 σ *1s 2 σ 2s 2 σ *2s 2 π 2py 2 π *2px 1 σ 2p 1 (c) σ 1s 2 σ *1s 2 σ 2s 2 σ *2s 2 π 2py 2 π 2px 2 (d) σ 1s 2 σ *1s 2 σ 2s 2 σ *2s 2 π 2py 1 π 2px 1 (e) σ 1s 2 σ *1s 2 σ 2s 2 σ *2s 2 π 2py 1 π *2py 1 π 2px 1 π *2px 1 3 of 10
8. Which of the molecules below (there is more than one) are diamagnetic? Mark each one on the scantron. (a) N2 - (b) O2 (c) F2 (d) B2 (e) Ne2 9. What is the bond order for a molecule of BN -? (a) 0 (b) 0.5 (c) 1.5 (d) 2 (e) 2.5 10. Which of the following molecules would you expect to have the lowest bond strength? Hint: determine their bond order. (a) CO (b) BN (c) F2 (d) N2 (e) O2 11. According to the valence bond theory, which is the best definition of an anti-bonding orbital? (a) A removal and transfer of electrons from one atom to another. (b) A side-by-side overlap of two p orbitals. (c) The out-of-phase overlap of atomic orbitals, resulting in a node along the internuclear axis. (d) The presence of two orbitals with the same energy near their respective nuclei. (e) A covalent bond formed by the overlap of atomic orbitals along the internuclear axis. 12. Which bonding theory best explains the geometry of individual molecules from the number of electron groups surrounding the center atom? (a) Molecular orbital theory (b) Valence shell electron pair repulsion (c) Valence bond theory (d) Quantum theory of atoms in molecules (e) Brannigan s law 4 of 10
13. From the following possible responses, select those that give the combination of bonds that makes up a triple covalent bond. (a) Two sigma bonds, one pi bond (b) one sigma bond, two pi bonds (c) Three sigma bonds (d) Three pi bonds (e) None of the above is right 14. Which of the following is the least electronegative? (a) F (b) Fr (c) O (d) S (e) N 15. Which of the following contains covalent bonds? (a) LiBr (b) MgF2 (c) NaCl (d) BrCl (e) Li 16. Select the compound with the lowest lattice energy (a) BaO (b) KCl (c) CaCl2 (d) MgO (e) CaS 17. Which of the following is an ionic compound (a) H2S (b) Kl (c) NH3 (d) I2 (e) CCl4 5 of 10
18. Select the element whose Lewis dot symbol is correct. (a) (b) (c) (d) (e) 19. The diameter of a chloride ion is 362 pm, and the diameter of a potassium ion is 276 pm. What is the distance between the nuclei of adjacent chloride and potassium ions in solid potassium chloride? (a) 1276 pm (b) 638 pm (c) 181 pm (d) 138 pm (e) 319 pm 20. Analysis of an unknown substance showed that it has a high boiling point and is brittle. It is an insulator as a solid but conducts electricity when melted. Which of the following substances would have those characteristics? (a) Al (b) HCl (c) SiF4 (d) I2 (e) KBr 21. Which one of the following properties is least characteristic of typical ionic compounds? (a) high melting point (b) high boiling point (c) poor electrical conductor when melted (d) poor electrical conductor when solid (e) brittleness 22. Select the strongest bond in the following group. (a) C C (b) C O (c) C N (d) C=C (e) C F 6 of 10
23. Arrange calcium, rubidium, sulfur, and arsenic in order of decreasing electronegativity. (a) S > As > Rb > Ca (b) S > As > Ca > Rb (c) As > S > Rb > Ca (d) As > S > Ca > Rb (e) None of the above orders is correct. 24. Select the most polar bonds amongst the following. (a) Si F (b) C O (c) Cl F (d) C F (e) C I 25. Select the best Lewis structure for NF3. (a) (b) (c) (d) (e) None of the above structures is suitable for NF3 26. Which of the following structures has resonance structures? (a) CO3 2 (b) O2 (c) SF6 (d) CO2 (e) NH3 7 of 10
27. The best Lewis structure for sulfuric acid (H2SO4) has zero formal charges, sulfur as the central atom, and no bonds between S and H. How many single and double bonds, respectively, are there in this Lewis structure? (a) 4 single, no double (b) 6 single, no double (c) 5 single, 1 double (d) 2 single, 4 double (e) 4 single, 2 double 28. The formal charge on Cl in the structure shown for the perchlorate ion is (a) +1 (b) +2 (c) 0 (d) -1 (e) -2 29. A sample of the inert gas krypton has its pressure tripled while its temperature remained constant. If the original volume is 12 L, what is the final volume? (a) 48 L (b) 36 L (c) 9 L (d) 6.0 L (e) 4.0 L 30. A sample container of carbon monoxide occupies a volume of 435 ml at a pressure of 785 torr and a temperature of 298 K. What would its temperature be if the volume were changed to 265 ml at a pressure of 785 torr? (a) 298 K (b) 182 K (c) 387 K (d) 489 K (e) 538 K 8 of 10
31. A sample of nitrogen gas is confined to a 14.0 L container at 375 torr and 37.0 C. How many moles of nitrogen are in the container? (a) 227 mol (b) 206 mol (c) 3.69 mol (d) 2.27 mol (e) 0.271 mol 32. Appropriate hybridization schemes for the C atoms in molecular CH3CO2H are: (a) sp 3 and sp (b) sp 3 and sp 2 (c) sp 2 and sp (d) sp 2 and sp 2 (e) sp 3 and sp 3 33. The F-S-F bond angles in SF6 are. (a) 109.5 o (b) 120 o only (c) 90 o and 120 o (d) 45 o and 90 o (e) 90 o and 180 o 34. Choose the species that is incorrectly matched with the electronic geometry about the central atom. (a) NO2 - - trigonal planar (b) ClO4 - - tetrahedral (c) SO3 2- - trigonal pyramidal (d) ClO3 - - tetrahedral (e) BrO4 - - tetrahedral 35. What kind of hybrid orbitals are utilized by the carbon atom in CF4 molecules? (a) sp (b) sp 2 (c) sp 3 (d) sp 3 d (e) sp 3 d 2 9 of 10
36. A neutral molecule having the general formula AX3E2 has two unshared pair of electrons on A. What is the hybridization of A? (a) sp (b) sp 2 (c) sp 3 (d) sp 3 d (e) sp 3 d 2 10 of 10