Liquids and solids are condensed
states of matter that have intermolecular forces.
Intermolecular forces
Physical attractions between separate molecules are intermolecular
forces. The weakest of these forces is present in all molecules,
London Dispersion Forces. It�s due to the
temporary ganging up of electrons on one side of the molecule. This
creates a temporary dipole that can be attracted to other dipoles,
temporary or permanent. Molecules with a permanent dipole can also
display Dipole-Dipole attractions, or
Ion-Dipole attractions with an ion. Since the ability to
form these attractions isn�t temporary, as with London Dispersion
Forces, dipole attractions are stronger. When a hydrogen atom is
bonded to a very electronegative atom, N, O or F, it forms a very
strong dipole. This extra strong dipole can form strong attractions
with an N, O or F on another molecule, called Hydrogen
Bonding, which is the strongest IMF.
Properties of liquids and solids
Liquids have definite volumes, but not definite shapes, the
particles are free to move past each other and they are not very
compressible. Solids have definite volumes and shapes, the
particles are not able to move past each other and they are not
compressible at all.
Vapor Pressure
Vapor pressure is created when molecules on the surface of a solid
or liquid have enough energy to escape the intermolecular forces and
become a gas. Once it is a gas, it can create pressure. As
temperature increases, more molecules have the minimum energy to
evaporate, and vapor pressure increases. At first, many molecules
escape and the volume of the solid or liquid decreases. But after a
while, some begin to collide with the surface of the liquid and
rejoin the liquid again. Eventually equilibrium is established.
Solids Structures
Amorphous solids have no repeating structure. Crystalline solids do
have a pattern of repeating units. Atomic solids have atoms as the
repeating unit and can be metallic (electrons are shared in a large
pool throughout the metal) or network (where each atom is covalently
bonded to each other atom) solids. Molecular solids have molecules
that are all covalently bonded to one another. Ionic solids have a
network of ions arranged to maximize electrostatic attractions and
minimize repulsions.
Phase Changes
During melting or boiling, intermolecular forces are broken. During
freezing or condensing, intermolecular forces are formed. The
melting/freezing point is when the vapor pressure of the solid and
liquid are equal and the two states of matter are at equilibrium.
The boiling/condensing point is when the vapor pressure of the
liquid is equal to the atmospheric pressure and is the temperature
when the two states of matter are at equilibrium.
