General Chemistry 1140 - A April 22, 2004 (6 Pages, 35 Parts) Name ______________________________________ Each of the 31 multiple choice questions counts 1.5 points. Give the letter of the correct answer. ____1. What is the term for the ability of an atom in a chemical bond to attract a shared electron pair? (a) bond moment (d) surface tension (b) dipole moment (e) viscosity (c) electronegativity ____ 2. Which species violates the octet rule? (a) NO (d) two of the above (b) PF3 (e) all of the above 1- (c) NO2 (f) none of the above ____3. How many pairs of nonbonding electrons are shown in the Lewis electron dot formula of the cyanide ion, CN1-? (a) 0 (d) 3 (b) 1 (e) 5 (c) 2 (f) none of the above ____ 4. What is the Formal Charge on the nitrogen atom in the nitrate ion? (a) 0 (d) -1 (b) +1 (e) -2 (c) +2 (f) -3 ____ 5. Which of the following is held together by ionic bonds? (a) CO2 (d) SO2 (b) Fe2O3 (e) XeO4 (c) P2O5 ____ 6. How many valence electrons are in a sulfur atom and a sulfide ion? (a) 6 and 6, respectively (d) 8 and 8, respectively (b) 6 and 8, respectively (e) none of the above (c) 8 and 6, respectively ____ 7. Which of the following bonds is very polar, but not ionic? (a) Na-Cl. (d) Cu-O. (b) N-O. (e) none of the above (c) I-Cl. ____ 8. List the molecules BeH2, BH3, NH3, and OH2 in order of increasing bond angle: (a) OH2 < NH3 < BH3 < BeH2 (b) NH3 < OH2 < BeH2 < BH3 (c) OH2 < BeH2 < BH3 < NH3 (d) OH2 < BeH2 < NH3 < BH3 (e) BH3 < NH3 < OH2 < BeH2 ____ 9. Molecular orbitals can be considered to be formed by the “overlap” of atomic orbitals. Which one of the overlap sketches below best describes H-Br bond in HBr? (a) A H Br Br H H Br (b) B A (c) C B C (d) D (e) E Br H Br H D E ____ 10. According to the general trends in the periodic table, which of the following is the most electronegative element? (a) B (d) O (b) Be (e) S (c) Na A ____ 11. A graph representing the relationship between energy and the distance between a hydrogen and bromine atom is shown at the right. Which statement is true about the HBr molecule? B (a) bond energy is B and bond length is A. (b) bond energy is A and bond length is B. (c) bond energy is B and bond length is D. 0 (d) bond energy is C and bond length is A. C (e) bond energy is C and bond length is D. D ____ 12. What is the molecular shape of an ammonia, NH3, molecule? (a) bent (angular) (d) trigonal planar (b) linear (e) T shape (c) trigonal pyramidal (f) none of the above ____ 13. What is the molecular shape of a methane, CH4, molecule? (a) bent (angular) (d) trigonal pyramidal (b) linear (e) square planar (c) tetrahedral (f) none of the above ____ 14. What is the molecular shape of a xenon tetrafluoride, XeF4, molecule? (a) bent (angular) (d) trigonal pyramidal (b) linear (e) square planar (c) tetrahedral (f) none of the above ____ 15. The best description of the CO bond in formaldehyde H2C=O, is: (a) two sigma bonds (d) a sigma and two pi bonds (b) two pi bonds (e) a delta bond and a pi bond (c) a sigma and a pi bond ____ 16. The best description of the CN bond in HCN is: (a) a sigma bond (d) a sigma bond and two pi bonds (b) a pi bond (e) three pi bonds (c) a sigma bond and a pi bond ____ 17. At the right are four “molecular orbital diagrams” for very large molecules with filled orbitals in black. The correct statement is: (a) A is an insulator and D is a conductor (b) A is an insulator and C is an p-type semiconductor (c) D is an insulator and B is an p-type semiconductor (d) D is an insulator and C is an p-type semiconductor (e) None of the above ____ 18. Which substances whose MO diagrams are above would be colorless? (a) only A (d) only C (b) only B (e) only D (c) only B and C ____ 19. Which element should be added in a very small amount to silicon to give MO diagram C? (a) arsenic (d) all of the above would work (b) carbon (e) none of the above would work (c) gallium ____20. The molecular orbitals in the sketch below with the same symmetry as MO C are (+ indicates location of the nuclei): (a) A and B (d) B and E (b) A and D (e) D and E (c) B and D A BC D E ____ 21. The bonding molecular orbitals in the sketch above are: (a) A and B (d) B, C, and E (b) A, B, and D (e) C, D, and E (c) A and D ____ 22. Which of the following molecules are polar? BeH2, BH3, and NH3 (a) BeH2 only (d) none are polar (a) BH3 only (e) all are polar (c) NH3 only ____ 23. The orbital geometry at the right is called: (a) octahedral (d) trigonal bipyramidal (b) pentaganal (e) trigonal planar (c) tetrahedral ____ 24. Which molecule(s), XeF2, ClF3, XeF4, and ClF5, have the same orbital geometries as that shown in Question 23? (a) only XeF2 (d) XeF4 and ClF5 (b) XeF2 and ClF3 (e) only ClF5 (c) ClF3 and XeF4 ____ 25. Which of the following molecules are polar? CF4, SF4, and XeF4 (a) CF4 only (d) CF4 and SF4 (b) SF4 only (e) CF4 and XeF4 (c) XeF4 only ____ 26. Which of the following molecules are polar? CO2, NO2, and SO2 (a) CO2 only (d) CO2 and NO2 (b) NO2 only (e) NO2 and SO2 (c) SO2 only ____ 27. Which of the following molecules are polar? ClF3, SF4, BrF5, (a) ClF3 only (d) none are polar (b) SF4 only (e) all are polar (c) BrF5 only ____ 28. Which of the following alkenes is polar? F Cl F (a) first F (b) second CC CC (c) both (d) neither Cl Cl F Cl ____ 29. Which of the following benzenes is polar? F (a) first F F (b) second F (c) both (d) neither ____ 30. Two allotropes of carbon are graphite and diamond. Bonding in graphite is delocalized while the bonding in diamond is not. The correct statement is: (a) Graphite conducts electricity and pure diamond is colored. (b) Pure graphite is colorless but impure graphite is colored. (c) Both graphite and diamond are good electrical conductors. (d) Both graphite and diamond are poor electrical conductors. (e) None of the statements are correct. ____ 31. List the bond lengths in N2, CO2, and H2O in increasing length: (a) N2 < CO2 < H2O. (d) CO2 < H2O < N2. (b) N2 < H2O < CO2.(e) H2O < CO2 < N2. (c) CO2 < N2 < H2O. (f) H2O < N2 < CO2. 32. (9%) Complete AND Balance the following as Net Ionic Equations: a. A solution of acetic acid was added to a solution of sodium carbonate and a gas was evolved. b. A solution of ammonium hydroxide was added to a solution of ferric sulfate and a rusty solid formed. 33. (5%) Estimate the reaction energy for the reaction: 2 H2 + O2 —> 2 H2O using the following bond energies: H-H = 435; O=O = 495; O-H = 460 kJ/mole. 34. (11%) Sometimes simple Lewis structures can answer our bonding questions and sometimes it cannot. When it fails, a more comprehensive bonding theory, such as Molecular Orbital Theory must be used.. The energies of the molecular orbitals of simple diatomic molecules is show below for both the small number of electrons and for large number of electrons. To answer the following, use: the letters of specific orbital(s); or formulas of the following “molecules” H2, He2, Li2, Be2, B2, C2, N2, O2, F2, Ne2; or the words TRUE or FALSE. _______ a. Orbital C is a sigma bonding orbital. A I _______ b. Orbitals K are pi antibonding orbitals. B J _______ c. Orbital L is a sigma orbital formed from two “s” orbitals. C K D _______ d. Three molecule with a bond order of 0. L E M _______ e. Three molecules with a bond order of 1. F N _______ f. Two molecules with a bond order of two. G O _______ g. Two molecules which are paramagnetic. H P _______ h. Two orbitals which are sigma bonding orbitals. _______ i. Two orbitals which are pi antibonding orbitals. _______ j. The maximum number of electrons that can be in orbital E is 4. _______ k. The first excited state of Li2 has one electron in orbital O and one in orbital N. 35. (25%) NOTE: There are five questions to be answered for each compound. For each of the following: 1) give the Lewis electron dot structures; 2) give a three dimensional sketch; 3) give the hybridization of the central atom; 4) give the approximate values of all bond angles; AND 5) state if the species has a dipole moment or not a. H2O b. CO2 c. SO2 d. BrF5 e. PF5 36. (5%) Calculate the Formal Charge on chlorine in each of the following: ________a. Cl2 ________b. HCl ________c. ClF3 ________d. HClO3 1- ________e. ClO4.