Chemistry 1C - Chapter 16 part 2 – CLAS

1. Assume the following is a two-dimensional structure of an ionic compound MxAy; where the radius of the cation is smaller than the anion. What is the empirical formula of this ionic compound?

2. Consider the following two-dimensional lattice: In this lattice, the darker smaller circles represent atom A, and the larger circles represent atom B. What is the formula of this compound?

a. AB b. A2B c. AB2 d. A2B3 e. A2B8

3. Consider the following three-dimensional unit cell: In this unit cell, the black spheres represent atom A, and the white spheres represent atom B. What is the formula of this compound?

a. A2B8 b. AB c. AB2 d. A2B e. A2B2

4. If the all of the following unit cells composed of the same atom had the same volume, which would produce the densest material?

a. hexagonal

b. face-centered cubic

c. body-centered cubic

d. simple cubic

e. face-centered cubic & hexagonal

5. Which of the following statements is/arefalse?

I. The hexagonal closest-packed structure is ABAB....

II. A body-centered cubic unit cell has four atoms per unit cell.

III. For unit cells having the same edge length, a simple cubic structure would have a smaller density than a body- centered cube.

IV. Atoms in a solid consisting of only one element would have six nearest neighbors if the crystal structure was a simple cubic array.

a. II, III only b. II, III, IV c. I only d. I, IV e. II only

6. Lead forms an FCC crystal lattice. If the molar volume of lead is 18 cm3/mol, then what will be the volume of a single unit cell?

a. 7.65x107 pm3 b. 7.65x109 pm3 c. 1.20x106 pm3 d. 1.20x108 pm3 e. None of these

7. Zinc crystallizes in a cubic closest packed structure. The radius of a zinc atom is 135 pm. Calculate the density in g/mL for solid zinc.

8. Titanium metal has a body-centered cubic unit cell. The density is 4.50 g/cm3. Calculate the atomic radius in angstroms of titanium. (1010Å= 1m)

9. X-rays with wavelength of 163 pm were used to analyze a pure element crystal with a density of 7.21 g/cm3. The angle of first-order diffraction was 33°. Determine the identity of the element if the unit cell was FCC.

10. If all of the octahedral holes in a FCC lattice of anions (Y) are filled by cations (M), what is the stoichiometry of the resulting compound?

a. M2Y b. M3Y4 c. MY2 d. MY

11. If an ionic compound with the formula MX2 forms a face-centered cubic unit cell with the cations (M2+) at the lattice points, the anions (X–) will occupy…

a. the center of each face in each unit cell.

b. half of the tetrahedral holes in each unit cell.

c. the cubic hole in the center of the each unit cell.

d. all of the tetrahedral holes in each unit cell.

e. all of the octahedral holes in each unit cell.

12. The ionic solid AB contains A+ ions and B–ions. The B– ions form an FCC array. The ionic radius of A+ is 60 pm, and the ionic radius of B– is 181 pm. Based solely on the radius ratio, Predict how many of which type of holes the A+ ions will occupy.

a. All of the tetrahedral holes

b. Half of the tetrahedral holes

c. All of the octahedral holes

d. Half of the octahedral holes

e. None of these is correct

13.In general, how can one increase the conductivity in pure semiconductors?

a. Increase the temperature

b. Decrease the temperature

c. Dope the semiconductor to produce a p-type semiconductor

d. Both A and C are correct

e. Both B and C are correct

14. Identify the type of solid for each of the following:

a. LiF

b. Ar

c. C

d. Br2

e. Pb

f. SiO2

g. CO2

Location in an
unit cell / Fraction of atom
in 3D unit cell / Fraction of atom
in 2D unit cell
corner / 1/8 / 1/4
edge / 1/4 / 1/2
face / 1/2 / 1
center / 1 / N/A