Molecules and Solids
Energy States and Spectra of
Bonding in Solids
Free-Electron Theory of Metals
Band Theory of Solids
Electrical Conduction in Metals,
Insulators, and Semiconductors
ANSWERS TO QUESTIONS
Ionic bonds are ones between oppositely charged ions.
A simple model of an ionic bond is the electrostatic
attraction of a negatively charged latex balloon to a
positively charged Mylar balloon.
Covalent bonds are ones in which atoms share
electrons. Classically, two children playing a short-range
game of catch with a ball models a covalent bond. On
a quantum scale, the two atoms are sharing a wave
function, so perhaps a better model would be two
children using a single hula hoop.
Van der Waals bonds are weak electrostatic forces:
the dipole-dipole force is analogous to the attraction
between the opposite poles of two bar magnets, the
dipole-induced dipole force is similar to a bar magnet
attracting an iron nail or paper clip, and the dispersion
force is analogous to an alternating-current electro-
magnet attracting a paper clip.
A hydrogen atom in a molecule is not ionized, but its
electron can spend more time elsewhere than it does in
the hydrogen atom. The hydrogen atom can be a location
of net positive charge, and can weakly attract a zone of
negative charge in another molecule.
Rotational, vibrational, and electronic (as discussed in Chapter 42) are the three major forms
of excitation. Rotational energy for a diatomic molecule is on the order of
the moment of inertia of the molecule. A typical value for a small molecule is on the order of
Vibrational energy is on the order of
is the vibration frequency
of the molecule. A typical value is on the order of 0.1 eV. Electronic energy depends on the
state of an electron in the molecule and is on the order of a few eV. The rotational energy can
be zero, but neither the vibrational nor the electronic energy can be zero.
If you start with a solid sample and raise its temperature, it will typically melt F
rst, then start
emitting lots of far infrared light, then emit light with a spectrum peaking in the near infrared,
and later have its molecules dissociate into atoms. Rotation of a diatomic molecule involves less
energy than vibration. Absorption and emission of microwave photons, of frequency
accompany excitation and de-excitation of rotational motion, while infrared photons, of
accompany changes in the vibration state of typical simple molecules.
The ranking is then b > d > c > a.