One of the most common materials that people always preferred to work with was metal. In each era, preference was given to different types of these amazing substances. So, IV-III millennia BC are considered the age of chalcolithic, or copper. Later it is replaced by a bronze one, and then the one that is still relevant today - iron comes into force.
Today it is generally difficult to imagine that once it was possible to do without metal products, because almost everything, from household items, medical instruments and ending with heavy and light equipment, consists of this material or includes individual parts of it. Why did metals manage to gain such popularity? In what features are manifested and how it is laid down in their structure, we will try to understand further.
The general concept of metals
“Chemistry. Grade 9” is a textbook used by schoolchildren. It is in it that metals are studied in detail. A large chapter is given to the consideration of their physical and chemical properties, because their diversity is extremely great.
It is from this age that it is recommended to give children an idea of these atoms and their properties, because adolescents can already appreciate the value of such knowledge. They perfectly see that the variety of objects, machines and other things surrounding them is basically just metallic in nature.
What is metal? From the point of view of chemistry, it is customary to attribute to these atoms those that have:
- a small number of electrons at the external level;
- exhibit strong reducing properties;
- have a large atomic radius;
- how simple substances possess a number of specific physical properties.
The basis of knowledge about these substances can be obtained by considering the atomic-crystalline structure of metals. It explains exactly all the features and properties of these compounds.
In the periodic system, most of the entire table is allocated to metals, because they form all the secondary subgroups and the main ones from the first to the third group. Therefore, their numerical superiority is obvious. The most common are:
- calcium;
- sodium;
- titanium;
- iron;
- magnesium;
- aluminum;
- potassium.
All metals have a number of properties that allow them to be combined into one large group of substances. In turn, these properties are explained precisely by the crystalline structure of metals.
Metal properties
The specific properties of the substances under consideration include the following.
- Metallic shine. All representatives of simple substances possess it, most of them with the same silver-white color. Only a few (gold, copper, alloys) differ.
- Durability and ductility - the ability to deform and recover quite easily. Different representatives expressed in varying degrees.
- Electrical conductivity and thermal conductivity is one of the main properties that determines the scope of the metal and its alloys.
The crystal structure of metals and alloys explains the cause of each of the indicated properties and speaks of their severity for each specific representative. If you know the features of such a structure, then you can influence the properties of the sample and adjust it to the desired parameters, which people have been doing for many decades.
Atomic-crystalline structure of metals
What is such a structure, what is characterized by? The name itself suggests that all metals are crystals in the solid state, that is, under ordinary conditions (except for mercury, which is a liquid). What is a crystal?
This is a conditional graphic image constructed by crossing imaginary lines through the atoms that line the body. In other words, every metal is made up of atoms. They are located in it not randomly, but very correctly and consistently. So, if you mentally combine all these particles into one structure, you will get a beautiful image in the form of a regular geometric body of any shape.
This is commonly called the crystal lattice of a metal. It is very complex and spatially three-dimensional; therefore, for simplicity, it’s shown not all of it, but only a part, of a unit cell. The combination of such cells, assembled together and reflected in three-dimensional space, and forms crystal lattices. Chemistry, physics, and metallurgy are sciences that study the structural features of such structures.
The unit cell itself is a set of atoms that are located at a certain distance from each other and coordinate a strictly fixed number of other particles around themselves. It is characterized by packing density, distance between composite structures, coordination number. In general, all these parameters are a characteristic of the whole crystal, and therefore reflect the properties manifested by the metal.
There are several types of crystal lattices. All of them are united by one feature - atoms are located in the nodes, and inside is a cloud of electron gas, which is formed by the free movement of electrons inside the crystal.
Types of crystal lattices
Fourteen variants of the lattice structure are usually combined into three main types. They are as follows:
- Volumetric-centered cubic.
- Hexagonal close-packed.
- Face centered cubic.
The crystal structure of metals was studied only thanks to electron microscopy, when it became possible to obtain large magnifications of images. And the classification of the types of gratings was first given by the French scientist Bravais, whose last names are sometimes called.
Space-centric grille
The structure of the crystal lattice of metals of this type is the following structure. This is a cube in the nodes of which there are eight atoms. Another one is located in the center of the free internal space of the cell, which explains the name "volume-centered".
This is one of the options for the simplest structure of the unit cell, and hence the entire lattice as a whole. The following metals have this type:
- molybdenum;
- vanadium;
- chromium;
- manganese;
- alpha iron;
- betta iron and others.
The main properties of such representatives are a high degree of malleability and ductility, hardness and strength.
Face centered grating
The crystal structure of metals having a face-centered cubic lattice is the following structure. This is a cube that includes fourteen atoms. Eight of them form the nodes of the lattice, and six more are located one on each face.
A similar structure has:
- aluminum;
- nickel;
- lead;
- gamma iron;
- copper.
The main distinguishing properties are gloss of different colors, lightness, strength, ductility, and increased resistance to corrosion.
Hexagonal grid
The crystal structure of metals having this type of lattice is as follows. The unit cell is based on a hexagonal prism. At its nodes there are 12 atoms, two more at the bases and three atoms freely lie inside the space in the center of the structure. Only seventeen atoms.
Such a complex configuration has such metals as:
- alpha titanium;
- magnesium;
- alpha cobalt;
- zinc.
The main properties are a high degree of strength, a strong silver sheen.
Defects in the crystal structure of metals
However, all considered cell types can have natural defects, or so-called defects. This may be due to various reasons: extraneous atoms and impurities in metals, external influences and others.
Therefore, there is a classification reflecting defects that may have crystal lattices. Chemistry as a science studies each of them in order to identify the cause and method of elimination, so that the properties of the material are not changed. So, the defects are as follows.
- Point. They are of three main types: vacancies, impurities, or dislocated atoms. They lead to a deterioration in the magnetic properties of the metal, its electrical and thermal conductivity.
- Linear, or dislocation. Allocate boundary and screw. The strength and quality of the material are deteriorating.
- Surface defects. Affect the appearance and structure of metals.
Currently developed methods for eliminating defects and obtaining pure crystals. However, they cannot be completely eradicated; an ideal crystal lattice does not exist.
The value of knowledge about the crystal structure of metals
From the above material, it is obvious that knowledge of the fine structure and structure allows us to predict the properties of the material and affect them. And this allows science to do chemistry. The 9th grade of a comprehensive school emphasizes in the learning process that students form a clear concept of the importance of a fundamental logical chain: composition - structure - properties - application.
Information about the crystalline structure of metals very clearly illustrates this dependence and allows the teacher to clearly explain and show children how important it is to know the fine structure in order to correctly and correctly use all the properties.