In nature, there are two types of solids that differ markedly in their properties. These are amorphous and crystalline bodies. And amorphous bodies do not have an exact melting point, they gradually soften during heating, and then pass into a fluid state. An example of such substances is resin or ordinary plasticine. But the situation is different with crystalline substances. They remain in a solid state until a certain temperature, and only when it reaches it, these substances melt.
It is all about the structure of such substances. In crystalline bodies, the particles of which they are composed are located at specific points. And if you connect them with straight lines, you get a kind of imaginary frame, which is called a crystal lattice. And the types of crystal lattices can be very different. And by the type of particles from which they are “built”, the lattices are divided into four types. These are ionic, atomic, molecular and metal lattices.
And in the nodes of the ionic crystal lattices, respectively, ions are located, and between them there is an ionic bond. These ions can be both simple (Cl-, Na +) and complex (OH-, SO2-). And these types of crystal lattices may contain some hydroxides and metal oxides, salts and other similar substances. Take, for example, ordinary sodium chloride. It alternates negative chlorine ions and positive sodium ions, which form a cubic crystal lattice. The ionic bonds in such a lattice are very stable and the substances “built” according to this principle have a sufficiently high strength and hardness.
There are also types of crystal lattices called atomic. Here in the nodes are atoms between which there is a strong covalent bond. Not many substances have an atomic lattice. These include diamond, as well as crystalline germanium, silicon and boron. There are some more complex substances that contain silicon oxide and have, respectively, an atomic crystal lattice. These are sand, quartz, rock crystal and silica. And in most cases, such substances are very durable, solid and refractory. They are also practically insoluble.
And molecular types of crystal lattices have a variety of substances. These include frozen water, that is, ordinary ice, “dry ice” - hardened carbon monoxide, as well as solid hydrogen sulfide and hydrogen chloride. Molecular lattices also have many solid organic compounds. These include sugar, glucose, naphthalene and other similar substances. And the molecules located in the nodes of such a lattice are interconnected by polar and nonpolar chemical bonds. And despite the fact that within the molecules between the atoms there are strong covalent bonds, these molecules themselves are held in the lattice due to very weak intermolecular bonds. Therefore, such substances are volatile enough, easily melt and do not have great hardness.
Well, metals have very different types of crystal lattices. And in their nodes can be both atoms and ions. At the same time, atoms can easily turn into ions, giving their electrons to “common use”. In the same way, ions, having “captured” a free electron, can become atoms. And such a structure of the metal crystal lattice determines such properties of metals as ductility, ductility, heat and electrical conductivity.
Also, the types of crystal lattices of metals, and other substances, are divided into seven main systems in the form of unit cells of the lattice. The simplest is a cubic cell. There are also rhombic, tetragonal, hexagonal, rhombohedral, monoclinic and triclinic unit cells that determine the shape of the entire crystal lattice. But in most cases, the crystal lattices are more complex than those listed above. This is due to the fact that elementary particles can be located not only in the nodes of the lattice themselves, but also in its center or on its faces. And among metals, the most common are such three complex crystal lattices: face-centered cubic, body-centered cubic, and close-packed hexagonal. The physical characteristics of metals also depend not only on the shape of their crystal lattice, but also on the interatomic distance and other parameters.