Gases

Gas is one of four classical states of matter.[1] Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into aliquid at its melting point (see phase change), boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which theelectrons are so energized that they leave their parent atoms from within the gas. A pure gas may be made up of individual atoms (e.g. a noble gas or atomic gas likeneon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixturewould contain a variety of pure gases much like the air. What distinguishes a gas from liquids and solids is the vast separation of the individual gasparticles. This separation usually makes a colorless gas invisible to the human observer. The interaction of gas particles in the presence of electric andgravitational fields are considered negligible as indicated by the constant velocity vectors in the image.

The gaseous state of matter is found between theliquid and plasma states,[2] the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale liedegenerative quantum gases[3] which are gaining increased attention these days.[4] High-density atomic gases super cooled to incredibly low temperatures are classifiedby their statistical behavior as either a Bose gas or a Fermi gas. For a comprehensive listing of these exotic states of matter see list of states of matter.