Which statement correctly describes a difference between graphene and graphite? (a) Graphene is a molecule but graphite is not. (b) Graphene is a single sheet of carbon atoms and graphite contains many, and larger, sheets of carbon atoms. (c) Graphene is an insulator but graphite is a metal. (d) Graphite is pure carbon but graphene is not. (e) The carbons are sp2 hybridized in graphene but sp3 hybridized in graphite.

Selected chlorides have the following melting points: NaCl (801 °C), MgCl₂ (714 °C), PCl₃ (-94 °C), SCl₂ (-121 °C) (a) For each compound, indicate what type its solid form is (molecular, metallic, ionic, or covalent-network).

Imagine the primitive cubic lattice. Now imagine pushing on top of it, straight down. Next, stretch another face by pulling it to the right. All angles remain 90°. What kind of primitive lattice have you made?

Pure iron crystallizes in a body-centered cubic structure, shown in the figure. but small amounts of impurities can stabilize a facecentered cubic structure. Which form of iron has a higher density?

What type of lattice—primitive cubic, body-centered cubic, or face-centered cubic—does each of the following structure types possess: (e) ZnS?

Silicon carbide, SiC, has the three-dimensional structure shown in the figure.

(b) Would you expect the bonding in SiC to be predominantly ionic, metallic, or covalent?

Energy bands are considered continuous due to the large number of closely spaced energy levels. The range of energy levels in a crystal of copper is approximately 1×10−19 J. Assuming equal spacing between levels, one can approximate the spacing between energy levels by dividing the range of energies by the number of atoms in the crystal. b. Determine the average spacing in J between energy levels in the copper metal in part (a).

Sodium oxide (Na2O) adopts a cubic structure with Na atoms represented by green spheres and O atoms by red spheres.

(c) The unit cell edge length is 5.550 Å. Determine the density of Na2O.

In their study of X-ray diffraction, William and Lawrence Bragg determined that the relationship among the wavelength of the radiation 1l2, the angle at which the radiation is diffracted 1u2, and the distance between planes of atoms in the crystal that cause the diffraction (d) is given by nl = 2d sin u. X rays from a copper X-ray tube that have a wavelength of 1.54 Å are diffracted at an angle of 14.22 degrees by crystalline silicon. Using the Bragg equation, calculate the distance between the planes of atoms responsible for diffraction in this crystal, assuming n = 1 (first-order diffraction).

Germanium has the same structure as silicon, but the unit cell size is different because Ge and Si atoms are not the same size. If you were to repeat the experiment described in Additional Exercise 12.117, but replace the Si crystal with a Ge crystal, would you expect the X rays to be diffracted at a larger or smaller angle 𝜃?

(a) The density of diamond is 3.5 g/cm³, and that of graphite is 2.3 g/cm³. Based on the structure of buckminsterfullerene, what would you expect its density to be relative to these other forms of carbon?

(b) X-ray diffraction studies of buckminsterfullerene show that it has a face-centered cubic lattice of C₆₀ molecules. The length of an edge of the unit cell is 14.2 Å. Calculate the density of buckminsterfullerene.

(a) What are the C—C—C bond angles in diamond?

(c) What atomic orbitals are involved in the stacking of graphite sheets with each other?

Employing the bond enthalpy values listed in Table 8.4, estimate the molar enthalpy change occurring upon (a) polymerization of ethylene. (b) formation of nylon 6,6. (c) formation of polyethylene terephthalate (PET).

Employing the bond enthalpy values listed in Table 8.3 estimate the molar enthalpy change occurring upon c. formation of polyethylene terephthalate (PET).

Although polyethylene can twist and turn in random ways, the most stable form is a linear one with the carbon backbone oriented as shown in the following figure:

The solid wedges in the figure indicate bonds from carbon that come out of the plane of the page; the dashed wedges indicate bonds that lie behind the plane of the page. (a) What is the hybridization of orbitals at each carbon atom? What angles do you expect between the bonds?

(a) In polyvinyl chloride shown in Table 12.6, which bonds have the lowest average bond enthalpy?

(b) When subjected to high pressure and heated, polyvinyl chloride converts to diamond. During this transformation which bonds are most likely to break first?

(c) Employing the values of average bond enthalpy in Table 8.3, estimate the overall enthalpy change for converting PVC to diamond.

Silicon has the diamond structure with a unit cell edge length of 5.43 Å and eight atoms per unit cell. (b) Suppose you dope that 1 cm3 sample of silicon with 1 ppm of phosphorus that will increase the conductivity by a factor of a million. How many milligrams of phosphorus are required?

One method to synthesize ionic solids is by the heating of two reactants at high temperatures. Consider the reaction of FeO with TiO₂ to form FeTiO₃. Determine the amount of each of the two reactants to prepare 2.500 g FeTiO₃, assuming the reaction goes to completion. (b) Calculate the formula weight of FeTiO₃.