states of matter
Forms (solid, liquid, or gas) in which material can exist. Whether a material is solid, liquid, or gaseous depends on its temperature and pressure. The transition between states takes place at definite temperatures, called the melting point and boiling point.
Kinetic theory describes how the state of a material depends on the movement and arrangement of its atoms or molecules. The atoms or molecules of gases move randomly in otherwise empty space, filling any size or shape of container. Gases can be liquefied by cooling as this lowers the speed of the molecules and enables attractive forces between them to bind them together. A liquid forms a level surface and assumes the shape of its container; its atoms or molecules do not occupy fixed positions, nor do they have total freedom of movement. Solids hold their own shape as their atoms or molecules are not free to move about but merely vibrate about fixed positions, such as those in crystal lattices.
| A hot ionized gas or plasma is often called the fourth state of matter, but liquid crystals, colloids, and glass also have a claim to this title. |
Change of state This occurs when a gas condenses to a liquid or a liquid freezes to a solid. Similar changes take place when a solid melts to form a liquid or a liquid vaporizes (evaporates) to form a gas. The first set of changes are brought about by cooling, the second set by heating. In the unusual change of state called sublimation, a solid changes directly to a gas without passing through the liquid state. For example, solid carbon dioxide (dry ice) sublimes to carbon dioxide gas. |
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