Lab 6 PostLab - Solid State Modeling - Sulaiman Aldhuhouri...

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Unformatted text preview: Sulaiman Aldhuhouri CH102, section 039, Spring 2012 Instructor: Trisha Lindenmuth TA WebAssign Lab 6 PostLab - Solid State Modeling (Postlab) Current Score : 25 / 25 Due : Monday, March 12 2012 11:00 PM EDT The due date for this assignment is past. Your work can be viewed below, but no changes can be made. Important! Before you view the answer key, decide whether or not you plan to request an extension. Your Instructor may not grant you an extension if you have viewed the answer key. Automatic extensions are not granted if you have viewed the answer key. Request Extension 1. 5/5 points | Previous Answers NCSUGenChem102LabV1 6.POST.01. Green checks and red X's are not displayed for this question. Match the picture to the type of cubic unit cell and rank the unit cells in their relative packing efficiency. Figure 1 Figure 2 Figure 3 Figure 1 Cell name Packing Body-centered cubic Face-centered cubic Body-centered cubic Face-centered cubic Medium efficiency Figure 2 Best Medium Best Figure 3 Simple cubic Simple cubic Lowest Lowest Lab 6 - Solid State Modeling 2. 5/5 points | Previous Answers NCSUGenChem102LabV1 6.POST.02. In modeling solid-state structures, atoms and ions are most often modeled as spheres. A structure built using spheres will have some empty, or void, space in it. A measure of void space in a particular structure is the packing efficiency, defined as the volume occupied by the spheres divided by the total volume of the structure. Given that a solid crystallizes in a face centered cubic structure that is 4.27 Å on each side, answer questions (a)-(e). (1 Å = 1. 10-10 m.) (a) How many total atoms are there in each unit cell? 4 4 atom(s) 3 (b) What is the volume of one unit cell in Å ? 77.9 77.9 Å 3 (c) Assuming that the atoms are spheres and the radius of each sphere is 1.51 Å, what is the volume of one atom in Å3? (Vsphere = 4/3πr3.) 14.4 14.4 Å3 (d) Therefore, what volume of atoms are in one unit cell? 57.6 57.6 Å3 (e) Based on your results from parts (b) and (d), what is the packing efficiency of the solid expressed as a percentage? 73.9 73.9 % Lab 6 - Solid State Modeling 3. 5/5 points | Previous Answers NCSUGenChem102LabV1 6.POST.03. Many metals pack in cubic unit cells. The density of a metal and length of the unit cell can be used to determine the type for 3 packing. For example, polonium has a density of 9.19 g/cm and a unit cell side length a of 3.37 Å. (1 Å = 1. 10 -8 cm.) (a) How many polonium atoms are in exactly 1 cm3? 2.66e22 2.66e+22 atoms (b) How many unit cells are in exactly 1 cm3? 2.61e22 2.61e+22 unit cells (c) How many polonium atoms are there per unit cell? 1 1 atom(s) (d) The atoms/unit cell suggests that polonium packs as a simple simple unit cell. Knowledge of the type of packing and side length a of the unit cell will allow calculation of the atomic radius, using one of the equations below. You may need to draw the unit cell to determine which formula to use to calculate the atomic radius. (e) What is the atomic radius of polonium? 1.69 1.69 Å Lab 6 - Solid State Modeling 4. 5/5 points | Previous Answers NCSUGenChem102LabV1 6.POST.04. Green checks and red X's are not displayed for this question. Use what you learned in lab about atoms in cubic structures to answer the following questions about a solid whose crystal structure was found to have atoms "A" in face sites and "B" in the corner and center sites of a cubic unit cell. How many "A"s are there in a unit cell? 3 3 "A"(s) How many "B"s are there in a unit cell? 2 2 "B"(s) What is the correct chemical formula for this solid? A2B3 A 3 B2 A3B4 AB3 A3B A4B3 A2B2 Use what you learned in lab about atoms in cubic structures to answer the following questions about a solid whose crystal structure was found to have atoms "C" in edge and center sites and "D" in the face sites of a cubic unit cell. How many "C"s are there in a unit cell? 4 4 "C"(s) How many "D"s are there in a unit cell? 3 3 "D"(s) What is the correct chemical formula for this solid? CD3 C3D C 4 D3 C2D3 C3D2 C3D4 C2D2 Lab 6 - Solid State Modeling 5. 5/5 points | Previous Answers NCSUGenChem102LabV1 6.POST.05. Green checks and red X's are not displayed for this question. Some ionic compounds crystallize in cubic cells. (a) The structure below has thallium atoms in corner and face sites and fluorine in edge and center sites of a cubic unit cell. How many thallium atoms are there in a unit cell? 4 4 atom(s) How many fluorine atoms are there in a unit cell? 4 4 atom(s) What is the correct chemical formula for this solid? Tl7F6 Tl4F3 Tl3F4 TlF Tl14F13 (b) If an ionic compound were composed of A 4+ and B‾, which unit cell structure would give a neutral compound? Lab 6 - Solid State Modeling ...
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