States of Matter and Intermolecular Forces

Refer to the "States of Matter and Intermolecular Forces" chapter for a discussion of intermolecular forces. 

Chapter 7, Physical Properties, provides examples of intermolecular forces and how they affect the state of matter and the physical properties of familiar compounds. 

This chapter is the first of two devoted to specific states of matter, and in it you will focus your attention on the gaseous state of matter. However, all of the states will be described within a larger framework that looks at the state of matter as a series of interrelated factors, including kinetic energy (or temperature), pressure, and intermolecular forces. Gases are usually described by a series of postulates known as kinetic molecular theory, which constitute the ideal gas law. To begin the chapter, you will look at a historical development of the ideal gas law, during which you will review some of the equations used to create the ideal gas law. 

Skill 1.3d-Relate intermolecular electrostatic forces, including Van derWaals, polar and induced polar, and ionic, to their expected states of matter and their characteristic physical properties... 

Although the notion of monomolecular surface layers is of fundamental importance to all phases of surface science, surfactant monolayers at the aqueous surface are so unique as virtually to constitute a special state of matter. For the many types of amphipathic molecules that meet the simple requirements for monolayer formation it is possible, using quite simple but elegant techniques over a century old, to obtain quantitative information on intermolecular forces and, furthermore, to manipulate them at will. The special driving force for self-assembly of surfactant molecules as monolayers, micelles, vesicles, or cell membranes (Fendler, 1982) when brought into contact with water is the hydrophobic effect. 

The state of matter in which a substance exists depends on the competition between the kinetic energy of the particles (proportional to temperature) and the strength of the intermolecular forces between the particles. 

The macroscopic properties of the three states of matter can be modeled as ensembles of molecules, and their interactions are described by intermolecular potentials or force fields. These theories lead to the understanding of properties such as the thermodynamic and transport properties, vapor pressure, and critical constants. The ideal gas is characterized by a group of molecules that are hard spheres far apart, and they exert forces on each other only during brief periods of collisions. The real gases experience intermolecular forces, such as the van der Waals forces, so that molecules exert forces on each other even when they are not in collision. The liquids and solids are characterized by molecules that are constantly in contact and exerting forces on each other. 

The previous chapter dealt with chemical bonding and the forces present between the atoms in molecules. Forces between atoms within a molecule are termed intramolecular forces and are responsible for chemical bonding. The interaction of valence electrons between atoms creates intramolecular forces, and this interaction dictates the chemical behavior of substances. Forces also exist between the molecules themselves, and these are collectively referred to as intermolecular forces. Intermolecular forces are mainly responsible for the physical characteristics of substances. One of the most obvious physical characteristics related to intermolecular force is the phase or physical state of matter. Solid, liquid, and gas are the three common states of matter. In addition to these three, two other states of matter exist—plasma and Bose-Einstein condensate. 

Intermolecular forces are responsible for the condensed states of matter. The particles making up solids and liquids are held together by intermolecular forces, and these forces affect a number of the physical properties of matter in these two states. Intermolecular forces are quite a bit weaker than the covalent and ionic bonds discussed in Chapter 7. The latter requires several hundred to several thousand kilojoules per mole to break. The strength of intermolecular forces are a few to tens of kilojoules per... 

This chapter continues to explore states of matter by focusing on the gas state. Table 8.1 summarized the main features of gases. In the gaseous state, molecules are much farther apart than in either solid or liquids. Because of this distance molecules in the gaseous state have virtually no influence on each other. The independent nature of gas molecules means intermolecular forces in this state are minimal. A gas expands to fill the volume of its container. Most of the volume occupied by the gas consists of empty space. This characteristic allows gases to be compressible, and gases have only about 1/1,000 the density of solids and liquids. 

Rationalize the defining characteristics of the states of matter in terms of intermolecular forces and the kinetic molecular theory of matter. 

---