Intermolecular Forces Liquids and Solids

After all the solid has been converted into a liquid, the temperature again starts to rise as energy is added. The particles are still relatively close together, but possess enough kinetic energy to move with respect to each other. Finally, if enough energy is added, the particles start to break free of 

These changes of state, called phase changes, are related to temperature, but sometimes pressure can influence the changes. We will see how these relationships can be diagrammed later in this chapter. 

No specific keywords or equations are listed on the AP exam for this topic. 

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Read and study Chapter 12, Solids, Liquids, and Intermolecular Forces. 

Two or more substances are separated by the differences in their affinity to paper or some other material. This affinity is related to the intermolecular forces between the substances. (See the chapter on Solids, Liquids, and Intermolecular Forces.)... 

The treatment of condensed phases, liquids and solids, has been reorganized into two chapters that contain much new material. Chapter 11 deals with liquids and intermolecular forces, while Chapter 12 deals with solids, starting from the basics of crystal structures and covering a broad range of materials (including metals, semiconductors, polymers, and nanomaterials) in a cohesive manner. 

Intermolecular forces are responsible for the existence of several different phases of matter. A phase is a form of matter that is uniform throughout in both chemical composition and physical state. The phases of matter include the three common physical states, solid, liquid, and gas (or vapor), introduced in Section A. Many substances have more than one solid phase, with different arrangements of their atoms or molecules. For instance, carbon has several solid phases one is the hard, brilliantly transparent diamond we value and treasure and another is the soft, slippery, black graphite we use in common pencil lead. A condensed phase means simply a solid or liquid phase. The temperature at which a gas condenses to a liquid or a solid depends on the strength of the attractive forces between its molecules. 

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. 

There are a few exceptions to the statements of the previous paragraph. The vibrational Raman spectrum of liquid H2 shows rotational fine structure for H2, the rotational levels are widely spaced and intermolecular forces are reasonably small. Certain solids when heated undergo a transition to a solid state in which molecular rotation in the crystal is possible. Solid H2 undergoes such a transition, as shown by the heat-capacity curve see Davidsoriy Section 16-9. 

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