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.
