These four occur naturally:
Solid: has a fixed shape and volume. The composite particles are very close together and don't move much. Solids can be crystalline or amorphous. Crystalline solids are very ordered. The atoms inside form a repeating structure. Examples are snowflakes and amethyst. There are also amorphous solids. The atoms are very disordered. An example is glass.
Liquid: has a fixed volume, but not a fixed shape. It will fit the container it is in. The composite particles are still close, but they can move around each other more. Examples are water and paint.
Gas: neither a fixed volume nor a fixed shape. It will fill any container you put it in. The particles can be close or very far apart, depending on how much pressure they are under. Examples are water vapor (steam) and oxygen.
Plasma: an ionized gas, full of electrons and ions. Neither a fixed volume nor a fixed shape. Read more about it here. Some examples include lightning and the sun.
However, there are also other things that don't quite fit into any of these categories.
Bose-Einstein Condensate (BEC): actually a 5th state of matter. However, it has never been seen in nature, so it is also called a "man-made" state of matter. It occurs at very low temperatures (only a few billionths of a degree above absolute zero). The atoms are virtually still, meaning they have very energy. Because of this the atoms are impossible to tell apart. And if they are impossible to tell apart, they are the same thing (physics is weird like that). So effectively, a BEC is one big atom.
Liquid Crystal: something between a crystalline solid and a liquid. The molecules tend to point in the same direction like a solid, but have more freedom of movement.
Non-Newtonian fluids: They are fluids, which means they are liquids or gases. However, all fluids have a property called viscosity, which is measures how much resistance there is to flow. For example, honey is more viscous than water. Ever heard the saying "As slow as molasses in January"? Viscosity varies inversely with temperature, so the hotter it is the better it flows (and vice versa). So molasses, which is already rather viscous, flows much more slowly in the cold winter months. In non-Newtonian fluids the viscosity also varies with the pressure applied to it. With shear-thickening (or dilatant) non-Newtonian fluids, the more pressure you add, the more viscous it gets (so it acts "thicker"). An example is Oobleck. With shear-thinning (or pseudoplastics), the more pressure you apply, the less viscous it gets. Examples include ketchup and paint.
Bingham Plastics: A special type of non-Newtonian fluid. It acts shear-thinning in the sense that the more pressure you apply the better it flows. However, the difference is that it starts out as a solid. An example is toothpaste.
Learn more:
http://www.seas.upenn.edu/~chem101/sschem/solidstatechem.html
http://www.sciencehq.com/chemistry/crystalline-and-amorphous-solids.html
http://www.plasmacoalition.org/edu.htm
http://www.chem4kids.com/files/matter_becondensate.html
http://www.nist.gov/public_affairs/releases/bec_background.cfm
http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.htm
http://dept.kent.edu/spie/liquidcrystals/
http://www.youtube.com/watch?v=UAqMDeq5hoA
http://www.teachengineering.org/view_lesson.php?url=collection/cub_/lessons/cub_surg/cub_surg_lesson03.xml
Liquid: has a fixed volume, but not a fixed shape. It will fit the container it is in. The composite particles are still close, but they can move around each other more. Examples are water and paint.
Gas: neither a fixed volume nor a fixed shape. It will fill any container you put it in. The particles can be close or very far apart, depending on how much pressure they are under. Examples are water vapor (steam) and oxygen.
Plasma: an ionized gas, full of electrons and ions. Neither a fixed volume nor a fixed shape. Read more about it here. Some examples include lightning and the sun.
 |
| Clockwise from top left this shows solid, liquid, plasma, and gas. |
However, there are also other things that don't quite fit into any of these categories.
Bose-Einstein Condensate (BEC): actually a 5th state of matter. However, it has never been seen in nature, so it is also called a "man-made" state of matter. It occurs at very low temperatures (only a few billionths of a degree above absolute zero). The atoms are virtually still, meaning they have very energy. Because of this the atoms are impossible to tell apart. And if they are impossible to tell apart, they are the same thing (physics is weird like that). So effectively, a BEC is one big atom.
Liquid Crystal: something between a crystalline solid and a liquid. The molecules tend to point in the same direction like a solid, but have more freedom of movement.
Non-Newtonian fluids: They are fluids, which means they are liquids or gases. However, all fluids have a property called viscosity, which is measures how much resistance there is to flow. For example, honey is more viscous than water. Ever heard the saying "As slow as molasses in January"? Viscosity varies inversely with temperature, so the hotter it is the better it flows (and vice versa). So molasses, which is already rather viscous, flows much more slowly in the cold winter months. In non-Newtonian fluids the viscosity also varies with the pressure applied to it. With shear-thickening (or dilatant) non-Newtonian fluids, the more pressure you add, the more viscous it gets (so it acts "thicker"). An example is Oobleck. With shear-thinning (or pseudoplastics), the more pressure you apply, the less viscous it gets. Examples include ketchup and paint.
Bingham Plastics: A special type of non-Newtonian fluid. It acts shear-thinning in the sense that the more pressure you apply the better it flows. However, the difference is that it starts out as a solid. An example is toothpaste.
Learn more:
http://www.seas.upenn.edu/~chem101/sschem/solidstatechem.html
http://www.sciencehq.com/chemistry/crystalline-and-amorphous-solids.html
http://www.plasmacoalition.org/edu.htm
http://www.chem4kids.com/files/matter_becondensate.html
http://www.nist.gov/public_affairs/releases/bec_background.cfm
http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.htm
http://dept.kent.edu/spie/liquidcrystals/
http://www.youtube.com/watch?v=UAqMDeq5hoA
http://www.teachengineering.org/view_lesson.php?url=collection/cub_/lessons/cub_surg/cub_surg_lesson03.xml
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