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Leader: Grant DeRocher Course: Chem 167 Supplemental Instruction Instructor: Houk Iowa State University Date: 03/05/13 Do a problem from end of ch 7 first as review. Then 8.10, 8.13, 8.17, 8.19, Next Exam is Wed March 13 2 hour Exam Review on Sunday March 10, Room TBD Ch 8 4. Polonium is the only metal that forms a simple cubic crystal structure. Use the fact that the density of polonium is 9.32g/cm3 to calculate its atomic radius. In the simple cubic crystal structure there are four Po atoms at the corners of each unit cell. The lengths of a unit cell, a, equals two times its radius, a=2r. The number of Po atoms resent in the simple cubic unit cell is 8*(1/8)=1 Po atom. The mass of one Po atoms is 1 πππ ππ 209 π ππ :1 ππ ππ‘ππ π 6.022π₯1023 ππ‘πππ ππ π 1 πππ ππ = 3.47π₯10−22 π. The volume of a unit cell is Vcell=(a)3 Using density we can solve for the volume in terms of the cell edge length, a, and then finally find a. π= d=m/v; π π = 3.47π₯10−22 π 9.32 π/ππ3 = 3.72π₯10−23 ππ3 . 3 So π = √3.72π₯10−23 = 3.34π₯10−8 cm. Now the cell edge a=2r so r=a/2 = 3.34x10-8/2= 1.67x10-8 cm 5. Europium forms a body-centered cubic unit cell and has density of 4.68g/cm3. From this information, determine the length of the edge of a cubic cell. The body centered cubic unit cell contains 8*(1/8) +1= 2 Eu atoms. 1 πππ πΈπ’ 152.97 π πΈπ’ The mass of these two atoms is: 2 πΈπ’ ππ‘πππ π 6.022π₯1023 ππ‘πππ πΈπ’ π 1 πππ πΈπ’ = 5.080π₯10−22 π The volume of this unit cell is Vcell= (a)3 Using density, we can solve for volume in terms of the cell edge length, a, and then finally find a. d= m/V π = So π = π = 5.080π₯10−22 π = 1.09π₯10−22 ππ3 4.68 π/ππ3 3 √1.09π₯10−22 ππ3 = 4.78π₯10−8 ππ π