# A structure of crystals

Imagine for a moment that your eyes have become so keen that they can see individual atoms or molecules. Wherever you look now, the structure of crystals opens before your eyes, and you notice the movement of particles. Looking at a gas, you will see the random movement of atoms, ions, molecules: individual particles, constantly moving, collide with each other. Particles also move randomly in the liquid, although here they are already placed more closely, each of them, as it were, tends to stay closer to its neighbors. And the particles of crystals move in a completely different way.

The structure of the crystals is correct, strictly regular. And in them, too, atoms, ions, molecules are not at rest, but the particles do not collide with each other, because they are all located in the correct order, and each can only oscillate around a certain position.

If you could get inside the crystal, you would see that even endless rows of particles stretch around you in all directions. In space, these regular rows of particles form the crystalline structure of crystals. And the structure of all crystalline substances is periodic and regular. In all crystals, particles line up in symmetrical regular rows, flat grids, three-dimensional lattices.

What happens when a liquid solidifies into a solid, such as when molten metal solidifies? In this case, the nature of the motion of particles of matter changes. In a solid crystalline substance, each particle moves "freely", oscillates, but only at its place in the system. The structure of the crystals is similar to a honeycomb or scaffolding: right and left, forward and backward, even, regular, endless rows of particles will stretch upwards.

However, particles of a solid can fail only if, for example, the crystal is heated so that it begins to melt. Under the warm rays of the spring sun, the ice heats up and begins to melt: this destroys the structure of particles in the ice crystal, weakens the forces that hold the particles in their places.

Order, regularity, periodicity, symmetry of the arrangement of atoms - this is what is characteristic of the structure of crystals. But, is the order, the structure of atoms in different solids the same? Of course not. Nature is infinitely varied and does not like repetition. The structure of iron atoms is not at all like the construction of an ice crystal. Each substance has its own characteristic pattern and arrangement of atoms. And the properties of the substance depend on what this order is. The same atoms, particles of the same sort, arranged in different ways, form substances with completely different properties.

Let's look at carbon atoms, for example. Soot, or soot, a soft black powder, is carbon. Coal, charcoal or stone, is also carbon. Graphite is a crystal composed of carbon atoms.

There is another form of carbon crystals - diamond, the most expensive and most beautiful of the precious stones. A faceted diamond is called a brilliant. Diamond is very hard, it is harder than all the stones on Earth.

It is hard to believe that diamond and graphite are made up of the same carbon atoms. Graphite is soft, opaque, black. Diamond is hard, transparent, sparkling with all the colors of the rainbow. Graphite is refractory, diamond burns easily. Try after that to doubt that diamond, graphite and soot consist of the same carbon atoms, and the difference is only in what is the structure of the arrangement of these atoms. They are arranged in one formation - and soft black graphite appears. Rebuild in a different way - and you get a solid transparent diamond.

The structure of crystals determines the properties of matter and its shape. And the correct polyhedral shape is a consequence of the atomic structure. Each crystalline substance can be distinguished from other crystalline substances by its atomic structure. In some crystals, the lattices are very simple, in others they are very complex. In different substances, the distances between particles in the lattice are different. But all these distances are very small, they are hundred-millionths of a centimeter (angstroms). To the question of what crystals are, the answer is as follows: crystals are substances in which their constituent particles (atoms, ions, molecules) are arranged strictly periodically, forming a geometrically regular crystalline structure.

A structure like that of crystals is found not only in natural polyhedrons of stones, in crystalline rocks and in metals, but also in very many other bodies. The vast majority of solids on Earth are crystalline. Only these crystals are for the most part not those beautiful polyhedrons that we admire in museums, but tiny grains, sometimes invisible to the eye. However, the internal structure of such nondescript grains is just as beautiful and surprisingly natural!