States of Matter for Ionic Compounds
- So far we have only discussed molecular compounds. These are the
only kind that can have "intermolecular forces". When these compounds
melt or boil Van der Waals bonds are being broken.
- Because ionic compounds don't have intermolecular forces, melting and boiling
involve the breaking of ionic bonds. That is why all ionic substances have
such high melting and boiling points. Sodium chloride for example melts at
801°C (1474°F) and boils at 1413°C (2575°F).
- The process of melting and boiling the same as molecular compounds in every
way except one: ionic bonds take the place of Van der Waals bonds. The image
below are of sodium chloride in several stages. (This could be used to illustrate
the solid, liquid, and gas phases of molecular compounds if you imagine that
each atom is a molecule and the bonds represented are weak intermolecular
bonds.)
(This image, used with permission, was created by C.H. Mak
at Virginia Tech. University)
Notice how the liquid model shows the atoms still close enough that the bonds
are still formed. However, bonds can break and reform with neighboring atoms.
In the gas model the atoms have enough energy to overcome even the strong attraction
of the ionic bond.