Gas

Article By:

Curtiss, Charles F. Formerly, Department of Chemistry, University of Wisconsin, Madison, Wisconsin.

Hirschfelder, J. O. Formerly, Department of Chemistry, University of Wisconsin, Madison, Wisconsin.

Last reviewed:November 2018

DOI:https://doi.org/10.1036/1097-8542.280300

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• Gas, published April 2014:Download PDF Get Adobe Acrobat Reader

A state of matter characterized by relatively low density, high fluidity, and lack of rigidity. A gas is one of the four fundamental states of matter—along with solid, liquid, and plasma—commonly encountered or observed (Fig. 1). A gas exists in between the states of liquid and plasma; that is, a gas will typically condense into a liquid, or be ionized into a plasma state, though a direct phase transition into a solid, known as deposition, that skips the liquid state can occur. The particles that compose a gas are far more spread out than those composing liquids and especially solids, and thus gas particles experience weaker intermolecular bonding. Gases have lower densities than liquids and solids and display no long-range order, as is found in crystalline solids. A gas expands readily to fill any containing vessel. See also: Amorphous solid; Chemical bonding; Crystal; Density; Intermolecular forces; Ionization; Liquid; Matter (physics); Phase rule; Phase transitions; Plasma (physics)

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