Samuel J. Ling; Jeff Sanny; William Moebs

Conceptual Questions

9.1 Types of Molecular Bonds

1.

What is the main difference between an ionic bond, a covalent bond, and a van der Waals bond?

2.

For the following cases, what type of bonding is expected? (a) KCl molecule; (b) $N_{2}$ molecule.

3.

Describe three steps to ionic bonding.

4.

What prevents a positive and negative ion from having a zero separation?

5.

For the $H_{2}$ molecule, why must the spins the electron spins be antiparallel?

9.2 Molecular Spectra

6.

Does the absorption spectrum of the diatomic molecule HCl depend on the isotope of chlorine contained in the molecule? Explain your reasoning.

7.

Rank the energy spacing $(Δ E)$ of the following transitions from least to greatest: an electron energy transition in an atom (atomic energy), the rotational energy of a molecule, or the vibrational energy of a molecule?

8.

Explain key features of a vibrational-rotation energy spectrum of the diatomic molecule.

9.3 Bonding in Crystalline Solids

9.

Why is the equilibrium separation distance between $K^{+} and {Cl}^{−}$ different for a diatomic molecule than for solid KCl?

10.

Describe the difference between a face-centered cubic structure (FCC) and a body-centered cubic structure (BCC).

11.

In sodium chloride, how many ${Cl}^{–}$ atoms are “nearest neighbors” of ${Na}^{+}$ ? How many ${Na}^{+}$ atoms are “nearest neighbors” of ${Cl}^{−}$ ?

12.

In cesium iodide, how many ${Cl}^{−}$ atoms are “nearest neighbors” of ${Cs}^{+}$ ? How many ${Cs}^{+}$ atoms are “nearest neighbors” of ${Cl}^{−}$ ?

13.

The NaCl crystal structure is FCC. The equilibrium spacing is $r_{0} = 0.282 nm$ . If each ion occupies a cubic volume of $r_{0}^{3}$ , estimate the distance between “nearest neighbor” ${Na}^{+}$ ions (center-to-center)?

9.4 Free Electron Model of Metals

14.

Why does the Fermi energy $(E_{F})$ increase with the number of electrons in a metal?

15.

If the electron number density (N/V) of a metal increases by a factor 8, what happens to the Fermi energy $(E_{F}) ?$

16.

Why does the horizontal line in the graph in Figure 9.12 suddenly stop at the Fermi energy?

17.

Why does the graph in Figure 9.12 increase gradually from the origin?

18.

Why are the sharp transitions at the Fermi energy “smoothed out” by increasing the temperature?

9.5 Band Theory of Solids

19.

What are the two main approaches used to determine the energy levels of electrons in a crystal?

20.

Describe two features of energy levels for an electron in a crystal.

21.

How does the number of energy levels in a band correspond to the number, N, of atoms.

22.

Why are some materials very good conductors and others very poor conductors?

23.

Why are some materials semiconductors?

24.

Why does the resistance of a semiconductor decrease as the temperature increases?

9.6 Semiconductors and Doping

25.

What kind of semiconductor is produced if germanium is doped with (a) arsenic, and (b) gallium?

26.

What kind of semiconductor is produced if silicon is doped with (a) phosphorus, and (b) indium?

27.

What is the Hall effect and what is it used for?

28.

For an n-type semiconductor, how do impurity atoms alter the energy structure of the solid?

29.

For a p-type semiconductor, how do impurity atoms alter the energy structure of the solid?

9.7 Semiconductor Devices

30.

When p- and n-type materials are joined, why is a uniform electric field generated near the junction?

31.

When p- and n-type materials are joined, why does the depletion layer not grow indefinitely?

32.

How do you know if a diode is in the forward biased configuration?

33.

Why does the reverse bias configuration lead to a very small current?

34.

What happens in the extreme case that where the n- and p-type materials are heavily doped?

35.

Explain how an audio amplifier works, using the transistor concept.

9.8 Superconductivity

36.

Describe two main features of a superconductor.

37.

How does BCS theory explain superconductivity?

38.

What is the Meissner effect?

39.

What impact does an increasing magnetic field have on the critical temperature of a semiconductor?