Chapter 12

Hydrogen bonding between polyamide chains plays an important role in determining the properties of a nylon such as nylon 6,6 (Table 12.5 ). Draw the structural formulas for two adjacent chains of nylon 6,6 and show where hydrogenbonding interactions could occur between them.

Explain why X-rays can be used to measure atomic distances in crystals but visible light cannot be used for this purpose.

In their study of X-ray diffraction, William and Lawrence Bragg determined that the relationship among the wavelength of the radiation $(\lambda ),$ the angle at which the radiation is diffracted $(\theta ),$ and the distance between planes of atoms in the crystal that cause the diffraction $(d)$ is given by $n\lambda =2d\sin \theta .$ X-rays from a copper X-ray tube that have a wavelength of $1.54\text{AA}$ 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).

The valence band of a semiconductor is made up of bonding molecular orbitals and the conduction band of antibonding molecular orbitals. (a) Given this fact would you expect n-type doping to strengthen or weaken the bonds in a semiconductor? (b) Would you expect p-type doping to strengthen or weaken the bonds in a semiconductor?

Spinel is a mineral that contains $37.9\mathrm{\%}$ Al, $17.1\mathrm{\%}\mathrm{Mg}$, and $45.0\mathrm{\%}\mathrm{O},$ by mass, and has a density of $3.57\mathrm{g}/{\mathrm{cm}}^3.$ The unit cell is cubic with an edge length of $8.09\text{AA}$. How many atoms of each type are in the unit cell?

(a) What are the $\mathrm{C}-\mathrm{C}-\mathrm{C}$ bond angles in diamond? (b) What are they in graphite?