states of matter


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states of matter,

forms of mattermatter,
anything that has mass and occupies space. Matter is sometimes called koinomatter (Gr. koinos=common) to distinguish it from antimatter, or matter composed of antiparticles.
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 differing in several properties because of differences in the motions and forces of the molecules (or atoms, ions, or elementary particles) of which they are composed. The states of matter are also known as phases of matter or states of aggregation. There are three commonly recognized states of matter: solidsolid,
one of the three commonly recognized states in which matter occurs, i.e., that state, as distinguished from liquid and gas, in which a substance has both a definite shape and a definite volume.
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, liquidliquid,
one of the three commonly recognized states in which matter occurs, i.e., that state, as distinguished from solid and gas, in which a substance has a definite volume but no definite shape.
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, and gasgas,
in physics, one of the three commonly recognized states of matter, the other two being solid and liquid. A substance in the gaseous state has neither definite shape nor definite volume. Like liquids, gases are fluids and assume the shape of their containers.
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. The molecules of a solid are limited to vibration about a fixed position. This restriction gives a solid both a definite volume and a definite shape. As energy in the form of heatheat,
nonmechanical energy in transit, associated with differences in temperature between a system and its surroundings or between parts of the same system. Measures of Heat
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 is added to a solid, its molecules begin to vibrate more rapidly until they break out of their fixed positions and the solid becomes a liquid. The change from solid to liquid is called melting and occurs at a definite temperature, the melting pointmelting point,
temperature at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific temperature; thus melting point is a characteristic of a substance and can be used
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. The molecules of a liquid are free to move throughout the liquid but are held from escaping from the liquid by intermolecular forces (see adhesion and cohesionadhesion and cohesion,
attractive forces between material bodies. A distinction is usually made between an adhesive force, which acts to hold two separate bodies together (or to stick one body to another) and a cohesive force, which acts to hold together the like or unlike
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). This gives a liquid a definite volume but no definite shape. As more heat is added to the liquid, some molecules gain enough energy to break away completely from the liquid and escape into the surrounding space (see evaporationevaporation,
change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity of the air,
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). Finally a temperature is reached at which molecules throughout the liquid are becoming energetic enough to escape and bubbles of vapor form and rise to the surface. The change of the liquid to a vapor, or gas, in this manner is called boiling and occurs at the boiling pointboiling point,
temperature at which a substance changes its state from liquid to gas. A stricter definition of boiling point is the temperature at which the liquid and vapor (gas) phases of a substance can exist in equilibrium.
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. The molecules of a gas are free to move in every possible way; a gas has neither a definite shape nor a definite volume but expands to fill any container in which it is placed. In addition to these three states of matter, scientists also distinguish three additional states—plasmaplasma,
in physics, fully ionized gas of low density, containing approximately equal numbers of positive and negative ions (see electron and ion). It is electrically conductive and is affected by magnetic fields.
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 and the Bose-Einstein and the fermionic condensatescondensate,
matter in the form of a gas of atoms, molecules, or elementary particles that have been so chilled that their motion is virtually halted and as a consequence they lose their separate identities and merge into a single entity.
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. A plasma is formed by adding still more heat to the molecules of a gas. Eventually a point is reached where the molecules are moving so rapidly that the molecules become torn apart into their component atoms and individual electrons are pulled away from the atoms. This very hot mixture of negatively charged electrons and positively charged ions has properties distinct from those of the other states of matter. Bose-Einstein condensate and fermionic condensates are formed by chilling the molecules of a gas. As temperatures approach absolute zero (−273.15°C), the motion of the individual atoms slows to the point where they combine to form a single "super atom" with properties distinct from those of other states of matter.

Bibliography

W. H. Bragg, Concerning the Nature of Things (2004).

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