PS3 - Assigned reading: 5.4-5.7, 15 Ch 102 Problem Set 3...

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Assigned reading: 5.4-5.7, 15 Ch 102 Problem Set 3 Due: Tuesday, April 19, before class Problem 1 (40 points) Part 1 Phosphorus pentachloride (PCl 5 ) is an important chemical that is often used as a chlorinating agent. To gain some insight into this molecule’s σ -bonding framework, we can apply molecular orbital theory to the simpler molecule PH 5 . Note: Do not run calculations with the provided software until you have built your MO diagram. a) Draw the structure of PH 5 using VSEPR, define a coordinate system (remember that by convention the principal axis of rotation is along the z axis), and assign its point group. b) Derive the reducible representation of the 5 H 1 s orbitals (the orbital basis set for the hydrogen atoms), Г 5H . Then reduce Г 5H to its irreducible representations. c) Draw all the SALCs that correspond to these irreducible representations. Label them clearly with their Mulliken symbols. d) Draw the valence orbitals of phosphorus (the orbital basis set for the central atom) and assign their irreducible representations. e) Construct an MO diagram by interacting the hydrogen SALCs with the phosphorus valence orbitals. Label each MO with the appropriate Mulliken symbol, also indicating the relative energy (e.g. 1e g , 2e g , etc.). Draw the MOs. Fill in the electrons. Label the HOMO and LUMO. What is the total bond order in PH 5 ? Do you predict this molecule to be paramagnetic or diamagnetic? f) Using the provided software, build PH 5 , run an optimization, and visualize the MOs MOs based on the selected atomic orbital basis set (do not analyze the core orbitals). Print out a small picture of each MO and assign its Mulliken symbol based on your MO diagram. g) Predict the relative P–H bond lengths in PH 5 and justify your reasoning. h) Draw the Lewis dot structure of PH 5 , including a resonance form that obeys the octet rule and one that is hypervalent. What is the total bond order predicted in each one? Based on the MO diagram you derived, which Lewis structure is more consistent with the bonding in PH 5 ? Do the MOs you calculated using the software support your answer? Explain.
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PS3 - Assigned reading: 5.4-5.7, 15 Ch 102 Problem Set 3...

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