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Characterization of solid state of matter. Crystals

Recall, usually the substance is called a solid, if it retains its shape and its volume. However, this is only the outward signs, characterizing the solid state of matter. From a physical point of view the presence of these signs does not allow to clearly distinguish between solid and liquid States of matter. On these grounds, for example, amorphous substances are solid, although the internal structure, they are liquids.

In the study of solids was found, many solids in nature have a smooth flat surface, located at right angles, and sometimes the shape of a regular polyhedra. Such solids are called crystals (from the Greek "mono" — one). Most often single crystals are very small in size, though, for example, the single crystals of rock crystal are sometimes the size of human growth.

The study of the internal structure of crystals using x-rays has allowed to establish, that particles in crystals (molecules, atoms and ions) I have the correct location, t. e. form crystal (spatial) bars. Point in the crystal lattice, corresponding to the most stable position of equilibrium of the particles of a solid, called the nodes of the grid.

The lattice sites are the correct location, which is repeated periodically within the crystal. This means, what if any the straight distance between nearest nodes is equal to α (rice. 11.1), the distance PA from the first node on this line in the crystal lattice will be the same p-th node. The location of the nodes in the crystal lattice repeats along any straight (I—IV in figure. 11.1). The correct location of the particles in the lattice sites of a crystal called long-range order in the arrangement of the particles.

So, in physics of solids under mean only such substances, have a crystalline structure. In other words, in the solid must be long-range order in the arrangement of its particles.

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