CHEM+1311+Exam+1 - CHEM 1311 Dr. Charlie Cox Summer 2009...

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Unformatted text preview: CHEM 1311 Dr. Charlie Cox Summer 2009 Guidelines: Exam #1, 100 points 16 June 2009 Name_______________________________ Closed NOTE/Closed BOOK 1. Write your name at the top of every page. 2. Turn off cell phones and other electronic devices other than a calculator. 3. Do not begin until instructed to do so. 4. No communication is permitted. 5. All materials must be put away. 6. One hour and 45 minutes is allotted for the exam. You may take a break as needed. 7. Please submit the exams when time is called. Instructions for submission will be provided. 8. SHOW all work for partial credit. 9. Regrade requests must be submitted one week after the exam is permitted. 10. GOOD LUCK! Useful Formulas and Constants: me = 9.11 x 10‐31 kg h = 6.626 x 10‐34 Js ao = 52.9 pm c = speed of light = 3.0 x 108 m/s Zeff = Z‐S RH = 2.18 x 10‐18 J 1. What are the quantum numbers for an electron in the f shell of Np. [4 points] n = __________, l = _________, ml = ___________ 2. How many radial and angular nodes are present in an 8f orbital? [4 points] Radial Nodes = _______________, Angular Nodes = ____________ 3. Rank the following in order of increasing radius: He+, Li2+, Be3+ [4 points] ________________ < _________________ < ______________ Smallest Largest 4. How many angular nodes are present in an s orbital? _________________ [1 point] 5. Heisenberg uncertainty principle states that we cannot know both the __________________ and _____________________ of an electron simultaneously. [2 points] 6. For the following trends, use >, <, or !"#$"%&'()*+&"#,&")&-.#*$/',*0"$+'&)1&%2 a. Ionization Energy [3 points] Sr ___________ Mg Cl ___________ S b. Atomic Radius [3 points] Np ___________ U Fe3+ __________ Fe2+ 7. a. Draw the Lewis structure for NO2‐. [3 points] b. c. What is the geometry and shape of NO2‐ around the central atom? [4 points] Geometry __________________________ Shape___________________________ Draw possible resonance forms if any. If no resonance exists explain why. [3 points] 8. a. Build an MO diagram for F2 complete with the appropriate number of electrons. Provide a brief sketch of the molecular orbitals formed. [9 points] b. Calculate the bond order for F2 based upon the MO diagram. [3 points] c. Is F2 paramagnetic or diamagnetic? Explain. [2 points] 9. (i.) (ii.) Identify the sign of the overlap integral, S, for the following combinations. [3 points] Identify the MO formed if any based upon the description. [4 points] i. ii. 10. Given the following structure, identify the hybridization of the identify orbitals. Circle the location of the pi bond and explain how the pi bond is formed based. _________ _________ __________ __________ ___________ ___________ (a.) (b.) (c.) (d.) Hybridization of sulfur (S) _____________________ [2 points] Hybridization of phosphorus (P) ________________ [2 points] Hybridization of Oxygen (O) ___________________ [2 points] Circle the system containing the pi bond. Explain how the pi bond is formed. [2 points] 11. Given HF, identify the atomic orbitals that are mixed and identify how many molecular orbitals will form andidentify how many nonbonding orbitals will be observed. [6 points] Sketch the MO diagram briefly illustrating the effect of electronegativity difference on the energy of the atomic orbitals. 12. 13. 14. Increase or decrease: a. b. c. d. e. f. As effective nuclear charge increases, ionization energy ______________. [1 point] As effective nuclear charge increases, atomic radii __________________. [1 point] As shielding increases, effective nuclear charge ____________________. [1 point] As nuclear charge increases, the energy ___________________________. [1 point] As bond order increases, bond length _____________________________. [1 point] As bond order increases, bond energy _____________________________. [1 point] As n ! 34"#,& energy of the system approaches ___________________. [1 point] Circle all of the polar molecules below [5 points]: NH3 SF4 XeF2 XeF4 BF3 15. Given the Zinc Blend structure, calculate each of the following: a. b. c. d. 16. How many sulfide atoms occupy the “face” site in the unit cell? ____________ [2 points] How many sulfide atoms occupy the “corner” site in the unit cell? __________ [2 points] How many zinc atoms are present in the unit cell? _______________________ [2 points] What is the coordination number of zinc? ______________________________ [1 point] If nickel metal crystallizes in an “fcc” lattice and has a radius of 149 nm. Calculate the density. Show all work and conclusions during this calculation. [7 points] 17. Calculate the enthalpy of formation of MgF2 using a Born‐Haber Cycle given the following parameters. [6 points] Mg (s) + F2 (g)! MgF2 (s) Lattice Energy ‐3916 kJ/mol 735 kJ/mol 1445 kJ/mol ‐328 kJ/mol 154 kJ/mol 150 kJ/mol First Ionization Energy of Mg Second Ionization Energy of Mg Electron Affinity of F Bond Energy of F2 Enthalpy of Sublimation of Mg 18. Draw a HOMO‐LUMO band for a conductor and semiconductor, and explain the significance of each. [4 points] EXTRA CREDIT 19. 20. What is the only country to be named after an element? Identify both the element and the country. [1 point] What is one application of selenium compounds? [1 point] ...
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