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Problem 61a,c
A particular form of cinnabar (HgS) adopts the zinc blende structure. The length of the unit cell edge is 5.852 Γ . (a) Calculate the density of HgS in this form. (c) Which of the two substances has the higher density? How do you account for the difference in densities?
Problem 61b
A particular form of cinnabar (HgS) adopts the zinc blende structure. The length of the unit cell edge is 5.852 Γ . (b) The mineral tiemannite (HgSe) also forms a solid phase with the zinc blende structure. The length of the unit cell edge in this mineral is 6.085 Γ . What accounts for the larger unit cell length in tiemmanite?
- At room temperature and pressure, RbI crystallizes with the NaCl-type structure. (a) Use ionic radii to predict the length of the cubic unit cell edge. (b) Use this value to estimate the density. (c) At high pressure, the structure transforms to one with a CsCl-type structure. Use ionic radii to predict the length of the cubic unit cell edge for the high-pressure form of RbI. (d) Use this value to estimate the density. How does this density compare with the density you calculated in part (b)?
Problem 62
Problem 63a
CuI, CsI, and NaI each adopt a different type of structure. The three different structures to consider are those shown in Figure 12.25 for CsCl, NaCl, and ZnS. a. Use ionic radii, Cs+(π=1.81 β«), Na+(π=1.16 β«), Cu+(π=0.74 β«), and, Iβ(π=2.06 β«), to predict which compound will crystallize with which structure.
- The coordination number for Mg2+ ion is usually six. Assuming this holds, determine the anion coordination number in the following compounds: (a) MgS, (b) MgF2, (c) MgO.
Problem 65
Problem 66a
The coordination number for the Al3+ ion is typically between four and six. Use the anion coordination number to determine the Al3 + coordination number in the following compounds: (a) AlF3 where the fluoride ions are two coordinate.
Problem 66b
The coordination number for the Al3+ ion is typically between four and six. Use the anion coordination number to determine the Al3 + coordination number in the following compounds: (b) Al2O3 where the oxygen ions are six coordinate.
Problem 66c
The coordination number for the Al3+ ion is typically between four and six. Use the anion coordination number to determine the Al3 + coordination number in the following compounds: (c) AlN where the nitride ions are four coordinate.
- Classify each of the following statements as true or false: (a) Although both molecular solids and covalent-network solids have covalent bonds, the melting points of molecular solids are much lower because their covalent bonds are much weaker. (b) Other factors being equal, highly symmetric molecules tend to form solids with higher melting points than asymmetrically shaped molecules.
Problem 67
- Classify each of the following statements as true or false: (a) For molecular solids, the melting point generally increases as the strengths of the covalent bonds increase. (b) For molecular solids, the melting point generally increases as the strengths of the intermolecular forces increase.
Problem 68
Problem 69a
Both covalent-network solids and ionic solids can have melting points well in excess of room temperature, and both can be poor conductors of electricity in their pure form. However, in other ways their properties are quite different. (a) Which type of solid is more likely to dissolve in water?
Problem 71
For each of the following pairs of semiconductors, which one will have the larger band gap: (a) CdS or CdTe? (b) GaN or InP? (c) GaAs or InAs?
Problem 73
If you want to dope GaAs to make an n-type semiconductor with an element to replace Ga, which element would you pick? a. Zn b. Al c. In or d. Si
- If you want to dope GaAs to make a p-type semiconductor with an element to replace As, which element(s) would you pick?
Problem 74
Problem 76b
Cadmium telluride is an important material for solar cells. (b) What wavelength of light would a photon of this energy correspond to?
Problem 76d
Cadmium telluride is an important material for solar cells. (d) With respect to silicon, does CdTe absorb a larger or smaller portion of the solar spectrum?
- The first LEDs were made from GaAs, which has a band gap of 1.43 eV. What wavelength of light would be emitted from an LED made from GaAs? What region of the electromagnetic spectrum does this light correspond to: ultraviolet, visible, or infrared?
Problem 78
- GaAs and GaP make solid solutions that have the same crystal structure as the parent materials, with As and P randomly distributed throughout the crystal. GaPxAs1 - x exists for any value of x. If we assume that the band gap varies linearly with composition between x = 0 and x = 1, estimate the band gap for GaP0.5As0.5. (GaAs and GaP band gaps are 1.43 eV and 2.26 eV, respectively.) What wavelength of light does this correspond to?
Problem 79
Problem 81
(a) What is a monomer? (b) Which of these molecules can be used as a monomer: ethanol, ethene (also called ethylene), methane?
- State whether each of these numbers is a reasonable value for a polymerβs molecular weight: 100 amu, 10,000 amu, 100,000 amu, 1,000,000 amu.
Problem 83
- Indicate whether the following statement is true or false: For an addition polymerization, there are no by-products of the reaction (assuming 100% yield).
Problem 84
Problem 86
Write a balanced chemical equation for the formation of a polymer via a condensation reaction from the monomers succinic acid 1HOOCCH2CH2COOH2 and ethylenediamine 1H2NCH2CH2NH22.
- An addition polymerization forms the polymer originally used as Saranβ’ wrap. It has the following structure β[CCl2βCH2]βn. Draw the structure of the monomer.
Problem 87
Problem 88b
Write the chemical equation that represents the formation of (b) polyacrylonitrile from acrylonitrile (polyacrylonitrile is used in home furnishings, craft yarns, clothing, and many other items).
Problem 92
What molecular structural features cause high-density polyethylene to be denser than low-density polyethylene?
- If you want to make a polymer for plastic wrap, should you strive to make a polymer that has a high or low degree of crystallinity?
Problem 93
Problem 94
Indicate whether each statement is true or false: (a) Elastomers are rubbery solids. (b) Thermosets cannot be reshaped. (c) Thermoplastic polymers can be recycled.
Problem 96a
CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (a) What color is the emitted light?
Problem 96b
CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (b) Would appropriately sized CdS quantum dots be able to emit blue light?
Problem 96c
CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (c) What about red light?