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CHEM 110 Atomic Radius

Write down your own detailed procedure before

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Unformatted text preview: detailed procedure before entering the lab. The material listed under APPARATUS AND CHEMICALS should also help. Make sure to have all Data Tables ready. Every reading or measurement must be recorded with the right units and number of significant figures (refer to the Theory section of Experiment 1 for further details and definitions). CALCULATIONS The whole strategy is based on the microscopic structure of the solid metal. We will consider each atom as a sphere, and a piece of solid metal as an assembly of spheres. There are several ways to assemble (or stack) spheres. Figure 1, below, shows one of them called Simple cubic. 2 You will note that having the spheres stacked directly over one another, leaves a lot of empty space between them. Most metals have their atoms packed in a much closer way. The different types of packing are called crystal structures. Table 1, below, gives the crystal structure of each candidate metals and the percentage of empty space in each structure. See if you can calculate the percentage of empty space for the structure displayed in Figure 1? The cube has 64 spheres, each side, therefore measuring 8r (r = radius of one sphere). Data and equations you will need volume V of a sphere: V = 4 r3/3 1 nanometer = 1nm = 10 9m 1 mol = 6.022 1023 1 mL = 1 cm3 Figure 1 – Simple cubic crystal structure of a solid metal, each sphere representing an atom. Table 1 Data for candidate metals Metal Molar Mass (g/mol) Al * Density (g/mL) Crystal structure Percentage of empty space (%) 26.9815 2.70 Face centered cubic 26 Ni 58.693 8.91 Face centered cubic 26 Cu 63.546 8.96 Face centered cubic 26 Mo 95.94 10.22 Face centered cubic 26 Sn 118.710 7.31 Tetragonal 40 Pb 207.2 11.35 Face centered cubic 26 Zn 65.39 7.13 Hexagonal 30 * at 25 C 3 The Crystal Structure sections of your textbook can help to complete the theoretical background if you find it necessary. Depending on the method you use, you may require the density of water. The chart from Experiment 1 is therefore provided below. Density of Water 1 Density (g/mL) 0.99 0.98 0.97 0.96 0.95 0 10 20 30 40 50 60 Temperature (Celsius) 4 70 80 90 100 Lab report, hand in before leaving the lab ATOMIC RADIUS Experiment 2 – Lab report Student first name last name student number Demonstrator Section (day + AM or PM) Date Include here: a short description of the procedure, the data tables you need(according to your procedure), write on the back if necessary 5 Lab report, hand in before leaving the lab Table X Identities and atomic radii of the unknowns Unknown code # Density Metal (experimental identity ) (g/mL) Density Atomic radius from Table 1 rel. accuracy (calculated) (g/mL) (%) (nm) Include here all the calculations done to complete ONE row of Table X. Questions 1. Calculate the percentage of empty space for the Simple cubic crystal structure. (Show all work) 6 Lab report, hand in before leaving the lab 2. Suppose there is a mistake in Table 1, and that the true crystal structure of all candidate metals is simple cubic. Recalculate the atomic radius for one of your unknowns. Also calculate the percent difference between this new radius and the one you have in Table X. (Show all work) 7...
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