State of matter
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In the physical sciences, a state of matter is one of the many ways that matter can interact with itself to form a macroscopic, homogenous phase. The most familiar examples of states of matter are solids, liquids, and gases; the most common state of matter in the universe is plasma. Less familiar phases include: quark-gluon plasma; Bose-Einstein condensates and fermionic condensates; strange matter; superfluids and supersolids, and possibly string-net liquids.
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[edit] Major differences between the common states of matter
It is useful for physicists to classify the different states of matter because there are common physical attributes that each state of matter shares.
For example, whereas both liquids and gases both have no long range order, they are distinguished from each other in that two gas phases must always be miscible in each other, whereas two liquid phases can be either immiscible (oil and water) or completely miscible (water and ethanol) or both, depending on temperature (methanol and hexane).
Neither liquids nor gases can sustain a stress without continually deforming, whereas solids can be resistant to deformation.
Unlike gases or liquids, solids can have anisotropic physical properties. That is, a physical property like strength or electrical conductivity can depend on the macroscopic direction in a solid, but not in a liquid or gas.
In general, the type of chemical bonds which hold matter together differ between the states of matter. For a gas, the chemical bonds are not strong enough to hold atoms or molecules together, and thus a gas is a collection of independent, unbonded molecules which interact mainly by collision. In a liquid, Van der Waals' forces or ionic interactions between molecules are strong enough to keep molecules in contact, but not strong enough to fix a particular structure, and the molecules can continually move with respect to each other. In a solid, metallic, covalent or ionic bonds provide cohesion between molecules, and the positions of atoms are fixed relative to each other over long time ranges. This being said, however, there is a great variety in the types of intermolecular bonds in the different materials classes: ceramics, metals, semiconductors or polymers, and each material or compound may be different.
[edit] The difference between phases and states of matter
States of matter are sometimes confused with phases. This is likely due to the fact that in many example systems, the familiar phase transitions are also transformations of the state of matter. In the example of water, the phases of ice, liquid water, and water vapor are commonly recognized. The common phase transitions observed in a one component system containing only water are melting/solidification (liquid/solid), evaporation/condensation (liquid/gas) and sublimation/deposition (solid/gas)
Transitions between different states of matter of the same chemical component are necessarily a phase transformation, but not all phase transformations involve a change in the state of matter. For example, there are 14 different forms of ice, all of which are the solid state of matter. When one form of ice transforms into another, the crystal structure, density and any number of physical properties changes, but it remains a solid.
Similarly, methanol and hexane are completely miscible liquids above approximately 42°C, but when a solution of the two is cooled below this temperature, the mixture separates into two phases, one rich in methanol, the other in hexane, although both resulting phases are the same state of matter -- liquids
The importance in distinguishing phases from states is especially important in multi-component systems. In these systems, the phase rule governs the equilibrium number of thermodynamically allowed unique phases and the number of degrees of freedom.
[edit] Other examples of states of matter
A plasma is similar in structure to a gas, but whereas in an ordinary gas the electrons are tightly bound to the atomic nuclei, in a plasma the atoms are ionized, i.e. electrons are separated from the atomic nuclei.
Bose-Einstein condensate is a state of matter that occurs at extremely low temperatures, near absolute zero. These temperatures are too low to occur anywhere on Earth except in laboratory experiments. The very slow motion of molecules at these temperatures allow some of the more bizarre aspects of quantum mechanics to manifest themselves in the form of novel macroscopic properties.
Under extremely high pressure, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as degenerate matter. These are of great interest to astrophysics, because these high-pressure conditions are believed to exist inside stars that have used up their nuclear fusion "fuel", such as white dwarves and neutron stars.
When in a normal solid state, the atoms of matter align themselves in a grid pattern, so that the spin of any electron is the opposite of the spin of all electrons touching it. But in a string-net liquid, atoms are arranged in some pattern which would require some electrons to have neighbors with the same spin. This gives rise to some curious properties, as well as supporting some unusual proposals about the fundamental conditions of the universe, itself.
[edit] External links
- 2005-06-22, MIT News: MIT physicists create new form of matter Citat: "... They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity."
- 2003-10-10, Science Daily: Metallic Phase For Bosons Implies New State Of Matter
- 2004-01-15, ScienceDaily: Probable Discovery Of A New, Supersolid, Phase Of Matter Citat: "...We apparently have observed, for the first time, a solid material with the characteristics of a superfluid...but because all its particles are in the identical quantum state, it remains a solid even though its component particles are continually flowing..."
- 2004-01-29, ScienceDaily: NIST/University Of Colorado Scientists Create New Form Of Matter: A Fermionic Condensate
[edit] See also
| States of Matter (list) |
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| Solid | Liquid | Gas | Plasma | Colloid | Supercritical fluid | Superfluid | Supersolid | Degenerate matter | Quark-gluon plasma | Fermionic condensate | Bose–Einstein condensate | Strange matter | Melting point | Boiling point | Triple point | Critical point | Equation of state | Cooling curve |
