In contrast to gases, solids and liquids have microscopic structures in which the constituent particles are very close together. The volume occupied by a given amount of a solid or liquid is much less than that of the corresponding gas. Consequently solids and liquids collectively are called condensed phases. The properties of solids and liquids are much more dependent on intermolecular forces and on atomic, molecular, or ionic sizes and shapes than are the properties of gases.
Solids on a submicroscopic level are arranged in repeating patterns. In the following page you will learn about two ways of thinking of these patterns: space lattices and unit cells.
Crystals are made up of many unit cells arranged in a repeating pattern. Here you can learn about the different forms the unit cell of a crystal can have.
An important class of crystal structures is found in many metals and also in the solidified noble gases where the atoms (which are all the same) are packed together as closely as possible.
Some materials are liquid on the microscopic scale (random arrangement) but appear to be solids microscopically (hard, highly rigid). Welcome to the world of amorphous materials.
The heat energy which a solid absorbs when it melts is called the enthalpy of fusion or heat of fusion and is usually quoted on a molar basis. (The word fusion means the same thing as “melting.”)
Vapor pressure is the result of the dynamic equilibrium that exists in every liquid. Read on to learn about what goes on at a microscopic level when you look a seemingly stable glass of water.
It is well known that boiling point depends on temperature. Most know that water boils at 100 degrees Celsius. However, in this section we learn that the boiling point of a liquid depends on pressure as well as temperature.
What happens when a gas becomes so dense it can no longer be called a gas? Here we learn about a special instance where the line between liquid and gas are blurred: critical temperature and pressure.
We often think of solutions as a combination of a liquid and a solid. Miscibility describes the behavior of solutions that are mixtures of 2 or more liquids.
Solubility is measured in many different ways, depending on the application. In this article, you will learn about how solubility is measured in a variety of scientific contexts.
Just as many of us sift through a trail mix for the chocolate, sometimes chemists need to "sift" through a mixture to isolate a certain substance. This section gives a broad intro into the tools chemists use to separate mixtures.
The colligative properties of a solution are those which depend on the number of particles (and hence the amount) of solute dissolved in a given quantity of solvent, irrespective of the chemical nature of those particles. We have already seen from Raoult’s law that the vapor pressure of a solution depends on the mole fraction of solute (amount of solute), and now we are in a position to see how this affects several other properties of solutions.
Osmosis occurs when two solutions of different concentrations are separated by a membrane which will selectively allow some species through it but not others. Then, material flows from the less concentrated to the more concentrated side of the membrane. A membrane which is selective in the way just described is said to be semipermeable. Osmosis is of particular importance in living organisms, since most living tissue is semipermeable in one way or another.
Solutions are homogeneous. Dissolved molecules as large as 1000 pm never separate as a result of gravitational forces, even in an ultracentrifuge. When suspended particles reach µm size, they separate readily under gravity, and we classify the mixture as definitely heterogeneous. Suspensions of particles between these sizes (5k - 200k pm) never settle under gravity or centrifugation, yet the mixtures are definitely heterogeneous because beams of light passing though them are visible.
