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- Silicon carbide, SiC, is a covalent network solid with a structure similar to that of diamond. Sketch a small portion of the SiC structure.
Problem 54
- Carbon and oxygen combine to form the molecular compound CO2, while silicon and oxygen combine to form a covalent network solid with the formula unit SiO2. Explain the difference in bonding between the two group 4A elements and oxygen.
Problem 57
- Potassium metal crystallizes in a body-centered cubic structure. Draw one unit cell, and try to draw an electron-dot structure for bonding of the central K atom to its nearestneighbor K atoms. What is the problem?
Problem 58
- The melting point of sodium metal is 97.8 °C, and the melting point of sodium chloride is 801 °C. What can you infer about the relative strength of metallic and ionic bonding from these melting points?
Problem 62
- Sodium melts at 98 °C, and magnesium melts at 650 °C. Account for the higher melting point of magnesium using the electron-sea model.
Problem 65
- Draw an MO energy-level diagram that shows the population of the 4s band for potassium metal.
Problem 67
- State whether each of the following compounds is likely to have a liquid crystalline phase. Explain your reasoning. (a)
Problem 68
- Draw an MO energy-level diagram for beryllium metal, and show the population of the MOs for the following two cases. (a) The 2s and 2p bands are well separated in energy. (b) The 2s and 2p bands overlap in energy. Which diagram agrees with the fact that beryllium has a high electrical conductivity? Explain.
Problem 70
- The melting points for the second-series transition elements increase from 1522 °C for yttrium to 2623 °C for molybdenum and then decrease to 321 °C for cadmium. Account for the trend using band theory.
Problem 72
- Tungsten is hard and has a very high melting point (3422 °C), and gold is soft and has a relatively low melting point (1064 °C). Are these facts in better agreement with the electron-sea model or the MO model (band theory)? Explain.
Problem 74
- Explain why the enthalpy of vaporization of vanadium (460 kJ/mol) is much larger than that of zinc (114 kJ/mol).
Problem 75
- Tell what is meant by each of the following terms. (c) Band gap
Problem 77
- Draw the bands of MO energy levels and the electron population for: (a) A semiconductor (b) An electrical insulator Explain why a semiconductor has the higher electrical conductivity.
Problem 78
- Classify the following semiconductors as n-type or p-type. (a) Si doped with In (b) Ge doped with Sb (c) Gray Sn doped with As
Problem 86
Problem 89
Write a balanced equation for the synthesis of the 2–6 semiconductor ZnTe by chemical vapor deposition from dimethylzinc, Zn(CH3)2, and diethyltellurium, Te(CH2CH3)2, assuming that the other product is gaseous propane (CH3CH2CH3).
- Arrange the following materials in order of increasing electrical conductivity. (a) Cu (b) Al2O3 (c) Fe (d) Pure Ge (e) Ge doped with In
Problem 90
- What are the main differences between an LED and a photovoltaic cell?
Problem 94
- Considering only electronegativity, rank the LED semiconductors made of solid solutions in order of increasing bandgap energy. Al0.40Ga0.60As, Al0.25Ga0.75As, Al0.05Ga0.95As
Problem 101
Problem 102a
A photovoltaic cell contains a p–n junction that converts solar light to electricity. (a) Silicon semiconductors with a band-gap energy of 107 kJ/mol are commonly used to make photovoltaic cells. Calculate the wavelength that corresponds to the band-gap energy in silicon.
Problem 103a
A photovoltaic cell contains a p–n junction that that converts solar light to electricity. An optimum semiconductor would have its band-gap energy matched to the wavelength of maximum solar intensity at the Earth's surface. (a) What is the color and approximate wavelength of maximum solar intensity at the Earth's surface? Refer to the figure for Problem 12.102.
Problem 103b
A photovoltaic cell contains a p–n junction that that converts solar light to electricity. An optimum semiconductor would have its band-gap energy matched to the wavelength of maximum solar intensity at the Earth's surface. (b) Which of the following semiconductors absorb at a wavelength matched with maximum solar intensity? CdTe with a band-gap energy of 145 kJ/mol or ZnSe with a band-gap energy of 248 kJ/mol.
- Gallium arsenide, a material used to manufacture laser printers and compact disc players, has a band gap of 130 kJ/mol. Is GaAs a metallic conductor, a semiconductor, or an electrical insulator? With what group 4A element is GaAs isoelectronic? (Isoelectronic substances have the same number of electrons.)
Problem 104
Problem 105b
Wide band-gap semiconductors have a band gap between 2 and 7 electron volts (eV), where 1 eV = 96.485 kJ/mol. The wide band-gap semiconductor GaN, used to construct the laser in Blu-ray DVD players, has a band gap of 3.44 eV. The material in the laser, GaxIn1-xN, has some indium substituted for gallium. (b) If the light from the device is blue, does partial substitution of indium for gallium increase or decrease the band gap of GaxIn1-xN compared to GaN?
- What is the coordination environment of the K+ ions in the fullerene-based superconductor K3C60?
Problem 112
- Looking at Figure 12.27 identify the coordination numbers of the Cu, Y, and Ba atoms.
Problem 113
Problem 115
The YBa2Cu3O7 superconductor can be synthesized by the solgel method from a stoichiometric mixture of metal ethoxides followed by heating in oxygen. How many grams of Y(OCH2CH3)3 and how many grams of Ba(OCH2CH3)2 are required to react with 75.4 g of Cu(OCH2CH3)2 and an excess of water? Assuming a 100% yield, how many grams of YBa2Cu3O7 are obtained?
- What is a ceramic, and what properties distinguish a ceramic from a metal?
Problem 116
- Why are oxide ceramics more corrosion-resistant than metals?
Problem 119
- Silicon nitride 1Si3N42, a high-temperature ceramic useful for making engine components, is a covalent network solid in which each Si atom is bonded to four N atoms and each N atom is bonded to three Si atoms. Explain why silicon nitride is more brittle than a metal like copper.
Problem 120
- Describe the reactions that occur when an Si1OH24 sol becomes a gel. What is the formula of the ceramic obtained when the gel is dried and sintered?
Problem 126