Chem 101 Book Answers (Ch.8)

Chem 101 Book Answers (Ch.8) - Chapter 8 Solid Materials 1....

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Chapter 8 Solid Materials 8-1 1. What is a unit cell? A unit cell is the smallest repeat unit of the crystal. 3. How many unit cells are shown in Figure 8.17b? Figure 8.17b is eight unit cells. A yellow sphere is at the center of each unit cell. 5. What is the Fermi level? The Fermi level is the energy of the occupied orbital that has the greatest energy. 7. What is a band gap? The band gap is the energy separation between the valence and conduction bands. 9. The band structures of a conductor, a semiconductor and an insulator are shown to the right. Identify each. A has the largest band gap, so it is the insulator. B has a partially filled band and is a metallic conductor. C is the semiconductor because its band gap is less than that of A. 11. Gold crystallizes in a face-centered cubic geometry that is 4.08 Å on each side. a, Draw a picure showing the face of the unit cell. See Figure 8.4b in the text. What atomic radus of gold is required for this geometry? Use Equation 8.1b for fcc unit cells and the given value of a, o 2a 2 4.08 r = = = 1.44 A 44 × b. How many gold atoms are present in the unit cell? fcc unit cells have 4 atoms. c. What is the volume of the unit cell in Å 3 ? V cell = a 3 = 4.08 3 = 67.9 Å 3 d. What is the volume occupied by the atoms in the unit cell? Volume of one atom = 4 3 π r 3 = 4 3 (1.44 3 ) = 12.5 Å; Volume of four atoms = V atoms = 4 x 12.5 = 50.0 Å e. Based on your results to c and d. what is the packing efficiency of the unit cell? How does this compare with the packing efficiency expected for a fcc unit cell?
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This note was uploaded on 10/30/2009 for the course CH Ch101 taught by Professor Bigham during the Fall '08 term at N.C. State.

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Chem 101 Book Answers (Ch.8) - Chapter 8 Solid Materials 1....

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