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Intermolecular Forces, Solids and Liquids 163
Don’t Forget!
Particles not in the center of a cell are shared by more then one cell. The contribution
from these particles will be only a fraction of the complete particle.
There are five types of crystalline solids:
1. Atomic solids have individual atoms held in place by London forces. The
noble gases are the only atomic solids known.
2. Molecular solids have their lattices composed of molecules held in place by
London forces, dipole-dipole forces, and hydrogen bonding. Solid methane
and water are example of molecular solids.
3. Ionic solids have their lattices composed of ions held together by the attraction
of opposite charges of the ions. These crystalline solids tend to be
strong with high melting points due to the strength of the intermolecular
forces. NaCl and other salts are example of ionic solids.
4. Metallic solids have metal atoms occupying the crystal lattice held together
by metallic bonding. In metallic bonding, the electrons of the atoms are
delocalized and free to move throughout the entire solid. This explains the
electrical and thermal conductivity as well as many of the other properties
of metals.
5. Network covalent solids have covalent bonds joining the atoms together in
the crystal lattice, which is quite large. Graphite, diamond, and silicon dioxide
(SiO2) are examples of network solids.
11-4 Phase Changes
An equilibrium exists between a liquid and its vapor. This is just one of several
equilibria that exist between the states of matter. A phase diagram is a graph
representing the relationship of all the states of matter of a substance. One type
of phase diagram relates the states to temperature and pressure. This type
allows us to predict which state of matter will exist at a certain temperature and
pressure combination. Figure 11-1 shows a general form of a phase diagram.
Note that the diagram has three general areas corresponding to the three states
of matter: solid, liquid, and gas. The line from A to C represents the change in
vapor pressure of the solid with temperature for the sublimation (going directly
from a solid to a gas without first becoming a liquid) equilibrium. The A to