One of the most common materials that people have always preferred to work with has been metal. In each era, preference was given to different types of these amazing substances. So, IV-III millennia BC are considered to be the age of Chalcolith, or copper. Later it was replaced by bronze, and then the one that is still relevant today - iron comes into force.
Today it is generally hard to imagine that it was once 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 separate parts out of him. Why did metals manage to gain such popularity? What are the features and how it is inherent in their structure, let's try to figure it out further.
General concept of metals
"Chemistry. Grade 9" is a textbook thatschoolchildren learning. It is in it that metals are studied in detail. Consideration of their physical and chemical properties is devoted to a large chapter, because their diversity is extremely large.
It is from this age that it is recommended to give children an idea about these atoms and their properties, because teenagers can already fully appreciate the value of such knowledge. They perfectly see that the variety of objects, machines and other things around them is based on a metallic nature.
What is metal? From the point of view of chemistry, it is customary to refer to these atoms as those that have:
- a small number of electrons in the outer level;
- show strong restorative properties;
- have a large atomic radius;
- how simple substances have a number of specific physical properties.
The basis of knowledge about these substances can be obtained by considering the atomic-crystal structure of metals. It explains all the features and properties of these compounds.
In the periodic system, most of the entire table is allocated for metals, because they form all 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, it is the crystal structure of metals that explains these properties.
Properties of metals
The specific properties of the substances under consideration include the following.
- Metal shine. All representatives of simple substances possess it, and most of them have the same silver-white color. Only a few (gold, copper, alloys) are different.
- Malleability and plasticity - the ability to deform and recover easily enough. For different representatives it is expressed to a different extent.
- Electrical 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 reason for each of the indicated properties and speaks about their severity in each particular 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 crystal structure of metals
What is such a structure, what is it characterized by? The name itself suggests that all metals are crystals in the solid state, that is, under normal 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 up the body. In other words, every metal is made up of atoms. They are located in it not randomly, but very regularly and consistently. So, if mentallycombine all these particles into one structure, you get a beautiful image in the form of a regular geometric body of any shape.
This is what is called the crystal lattice of the metal. It is very complex and spatially voluminous, therefore, for simplicity, not all of it is shown, but only a part, an elementary cell. The set of such cells, brought together and reflected in three-dimensional space, forms crystal lattices. Chemistry, physics and metal science are sciences that study the structural features of such structures.
The elementary 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 them. It is characterized by the packing density, the distance between the constituent structures, and the coordination number. In general, all these parameters are a characteristic of the entire crystal, and therefore reflect the properties of the metal.
There are several varieties of crystal lattices. All of them are united by one feature - there are atoms in the nodes, and inside there is a cloud of electron gas, which is formed by the free movement of electrons inside the crystal.
Types of crystal lattices
Fourteen options for the structure of the lattice are usually combined into three main types. They are as follows:
- Body-Centered Cubic.
- Hexagonal close-packed.
- Face-centered cubic.
The crystal structure of metals was only studied through electron microscopy, when it became possible to obtain large magnifications of images. And the classification of the types of lattices was first introduced by the French scientist Bravais, by whose name they are sometimes called.
Body-Centered Lattice
The structure of the crystal lattice of metals of this type is the following structure. This is a cube, at 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 "body-centered".
This is one of the options for the simplest structure of the elementary cell, and hence the entire lattice as a whole. The following metals have this type:
- molybdenum;
- vanadium;
- chrome;
- 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 lattice
The crystal structure of metals having a face-centered cubic lattice is the following structure. This is a cube, which includes fourteen atoms. Eight of them form the lattice nodes, and six more are located one on each face.
They have a similar structure:
- aluminum;
- nickel;
- lead;
- gamma iron;
- copper.
Main distinguishing properties - shinedifferent colors, lightness, strength, malleability, increased resistance to corrosion.
Hexagonal lattice
The crystal structure of metals with this type of lattice is as follows. The elementary cell is based on a hexagonal prism. There are 12 atoms in its nodes, two more at the bases and three atoms freely lie inside the space in the center of the structure. Seventeen atoms total.
Metals such as:
have a similar complex configuration
- alpha titan;
- magnesium;
- alpha cob alt;
- zinc.
Main properties - high strength, strong silver luster.
Defects in the crystal structure of metals
However, all considered types of cells may have natural flaws, or so-called defects. This may be due to various reasons: foreign atoms and impurities in metals, external influences, and others.
Therefore, there is a classification that reflects the defects that crystal lattices can have. Chemistry as a science studies each of them in order to identify the cause and remedy so that the properties of the material are not changed. So the defects are as follows.
- Point. They come in 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 marginal and screw. Degrade the strength and quality of the material.
- Surfacedefects. Affect the appearance and structure of metals.
Currently, methods have been developed to eliminate defects and obtain pure crystals. However, they cannot be completely eradicated, the 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 makes it possible to predict the properties of the material and influence them. And this allows you to do the science of chemistry. Grade 9 of a general education school focuses on teaching students a clear understanding of the importance of the fundamental logical chain: composition - structure - properties - application.
Information about the crystal structure of metals illustrates this relationship very clearly and allows the teacher to clearly explain and show children how important it is to know the fine structure in order to correctly and competently use all properties.
