1. A View From A Distant Universe   Previous PageNext Page
    The States of Matter

Gases are not the only form of matter in the universe. Liquids and solids also exist, especially with larger molecules and at lower temperatures. Every atom or molecule has a weak attraction for other atoms and molecules, or a "stickiness" on contact, known as van der Waals attraction. If the temperature is low and the energy of motion of a collection of molecules is small enough, this van der Waals attraction will hold the molecules together in a liquid. The molecules remain in contact but are free to slide past one another. At even lower temperatures and molecular energies, this freedom of motion is reduced further, and the molecules become locked into the frozen geometry of a solid.

Tiny particles such as He and must be cooled to extremely low temperatures before they condense to a liquid or freeze to a solid. Larger molecules with more surface area have greater van der Waals "stickiness," and occur as liquids or solids at room temperature.

Some atoms can gain or lose electrons to become electrically charged ions. These ions are held together in solids known as salts by the electrostatic forces between ions of opposite charge. After the study of bond-making-and-breaking reactions that molecules can undergo, one of the most important areas of chemistry is to explain the behavior and properties of substances in terms of the interactions between the molecules of which they are made.

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