课程名称︰普通化学一 课程性质︰必修 课程教师︰郑原忠 开课学院：理学院 开课系所︰化学系 考试日期（年月日）︰100年11月30日 考试时限（分钟）：120分钟 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : General Chemistry (I) Mid-term Exam #2 Date: 11/30/2011 (110 points) 1.(5%) Write the chemical formulas for the following compounds: (a) Silver cyanide (b) Calcium hypochlorite (c) Lithium hydride (d) Sodium peroxide (e) Ammonium dichromate 2.(10%) For each of the following molecules, give the Lewis structure and or nonpolar) for each molecule. (a) CBr4 (b) ClO2(-) (c) ICl3 (d) PF3 (e) SO3 3.(25%) (a)(5%) The Born-Oppenheimer approximation is the foundation of quantum chemistry. State the approximation and explain how it is applied in the MO theory of the hydrogen molecule. (b)(5%) Explain what "LCAO-MO" is. Specify the two basis fundations used in this model (denote the nature of the functions; there is no need to give the exact mathematical formulas) and give the expression for the two molecular orbitals. You should give symmetry arguments to justify your results and label the two molecular orbitals based on their symmetries. (c)(5%) Give the normalization constant for each of the two molecular orbi- tals in terms of the overlap integral of the two basis functions. Draw a qualitative MO correlation diagram to denote the energy le- vels of atomic and molecular orbitals (d)(5%) Fill the MOs with two electrons and give the approximate electronic wave function of the H2 molecule. Note that you need to consider electron spin and indistinguishability of electrons. (e)(5%) Use the MO correlation diagram to predict the bond orders of H2(+), H2, He2(+), and He2. Sort the four molecules from low to high bond energies. 4.(10%) Consider nitric oxide (NO), which is a major pollutant produced during combustion. (a)(5%) Draw a MO correlation diagram for the molecule, and denote its electron configuration in the electronic groud state. What is the bond order of NO? (b)(5%) Predict whether the nitrosyl (NO(+)) will have a shorter or longer bond than the NO molecule. Will NO(+) be paramagnetic like NO or diamagnetic? 5.(10%) Compare the bonding in formic acid (HCOOH) with that in its conjugate base formate ion (HCOO(-)). Draw Lewis diagrams, determine the hybri- dization of the carbon atom, and give the molecular geometries. How do the π orbitals differ in the two molecules? Give the bond orders to the four C-O bonds in the two molecules and sort the four C-O bonds from short to long bond lengths. 6.(10%) The molecular structure of cortisone is given on the right. (请自行用 wiki找"cortisone"英文版页面, 出现的结构图同考卷上的附图) This steroid is a drug that reduces inflammation and moderates allergic responses. Name all the functional groups in the molecule. How many chiral centers exist in the molecule? How many stereoisomers can be derived from this molecule (ignore conformers)? 7.(10%) Use Hückel MO theory to construct π molecular orbitals for cyclobuta- diene and predict molecular properties. (a)(5%) Draw the MO correlation diagram and sketch the π MOs. Indicate the degeneracies of these orbitals. The lowest energy MO is located at the energy α+2β. Use this information to correctly assign the energy lecels of all other MOs. (b)(2%) Show the number of electrons occupying each π MO in the ground state. Is cyclobutadiene paramagnetic in its ground state? (c)(3%) Calculate the delocalization energy of cyclobutadiene. Is cyclobu- tadiene aromatic? 8.(15%) The octahedral complex ion [MnCl6]^(3-) has more unpaired spins than the octahedral complex ion [Mn(CN)6]^(3-). (a)(5%) Give the splitting of the Mn d orbitals in the octahedral field. Explain your results. (b)(2%) How many unpaired electrons are present in the two complex ions? (c)(3%) In each case, calculate the crystal field stabilization energy in terms of Δo. (d)(5%) Why Cl(-) is a weak-field ligand whereas CN(-) is a strong-field ligand? 9.(15%) Answer ture or false for the following statements (3 points each): (a) Order of absorption wavelengths: [Cr(CN)6]^(3-) > [Cr(NH3)6]^(3+) > [Cr(H2O)6]^(3+). (b) Order of the absolute values of hydration enthalpies: Mn(3+) > Cr(2+) > Mn(2+) > Ca(2+). (c) Butyl acetate can be produced from butanol and acetic acid. (d) The bridge between photoelectron spectrum and MO theory is the Koopman's theorem, which states that the orbital energy in the LCAO-MO method is the ionization energy of an electron in the orbital. (e) The LCAO-MO method always predicts a higher ground state energy than the exact result. --

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