What bodies are called crystalline and amorphous. Amorphous and crystalline bodies, their properties

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In solids, particles (molecules, atoms, and ions) are located so close to each other that the forces of interaction between them do not allow them to fly apart. These particles can only make oscillatory motions around the equilibrium position. Therefore, solid bodies retain their shape and volume.

According to their molecular structure, solids are divided into crystalline And amorphous .

The structure of crystalline bodies

Crystal cell

Such solids are called crystalline, in which molecules, atoms or ions are arranged in a strictly defined geometric order, forming a structure in space, which is called crystal lattice . This order is periodically repeated in all directions in three-dimensional space. It persists over long distances and is not limited in space. He is called long-range order .

Types of crystal lattices

A crystal lattice is a mathematical model that can be used to represent how particles are arranged in a crystal. Mentally connecting in space with straight lines the points where these particles are located, we will get a crystal lattice.

The distance between atoms located at the nodes of this lattice is called lattice parameter .

Depending on which particles are located at the nodes, crystal lattices are molecular, atomic, ionic and metallic .

Such properties of crystalline bodies as melting point, elasticity, and strength depend on the type of crystal lattice.

When the temperature rises to a value at which the melting of the solid begins, the crystal lattice is destroyed. Molecules get more freedom, and the solid crystalline substance passes into the liquid stage. The stronger the bonds between molecules, the higher the melting point.

molecular lattice

In molecular lattices, bonds between molecules are not strong. Therefore, under normal conditions, such substances are in a liquid or gaseous state. The solid state for them is possible only at low temperatures. Their melting point (transition from solid to liquid) is also low. And under normal conditions, they are in a gaseous state. Examples are iodine (I 2), "dry ice" (carbon dioxide CO 2).

atomic lattice

In substances that have an atomic crystal lattice, the bonds between atoms are strong. Therefore, the substances themselves are very solid. They melt at high temperatures. Silicon, germanium, boron, quartz, oxides of some metals, and the hardest substance in nature, diamond, have a crystalline atomic lattice.

Ionic lattice

Substances with an ionic crystal lattice include alkalis, most salts, oxides of typical metals. Since the attractive force of ions is very high, these substances can only melt at very high temperatures. They are called refractory. They have high strength and hardness.

metal grate

At the nodes of the metal lattice, which all metals and their alloys have, both atoms and ions are located. Due to this structure, metals have good malleability and ductility, high thermal and electrical conductivity.

Most often, the shape of the crystal is a regular polyhedron. The faces and edges of such polyhedra always remain constant for a particular substance.

A single crystal is called single crystal . It has a regular geometric shape, a continuous crystal lattice.

Examples of natural single crystals are diamond, ruby, rock crystal, rock salt, Icelandic spar, quartz. Under artificial conditions, single crystals are obtained in the process of crystallization, when solutions or melts are cooled to a certain temperature and a solid substance in the form of crystals is isolated from them. With a slow crystallization rate, the faceting of such crystals has a natural shape. In this way, under special industrial conditions, for example, single crystals of semiconductors or dielectrics are obtained.

Small crystals, randomly fused with each other, are called polycrystals . The clearest example of a polycrystal is granite. All metals are also polycrystals.

Anisotropy of crystalline bodies

In crystals, particles are located with different densities in different directions. If we connect atoms in a straight line in one of the directions of the crystal lattice, then the distance between them will be the same in all this direction. In any other direction, the distance between the atoms is also constant, but its value may already differ from the distance in the previous case. This means that interaction forces of different magnitude act between atoms in different directions. Therefore, the physical properties of matter in these directions will also differ. This phenomenon is called anisotropy - the dependence of the properties of matter on direction.

Electrical conductivity, thermal conductivity, elasticity, refractive index and other properties of a crystalline substance differ depending on the direction in the crystal. Electric current is conducted differently in different directions, matter is heated differently, light rays are refracted differently.

Anisotropy is not observed in polycrystals. The properties of matter remain the same in all directions.

There are several states of aggregation in which all bodies and substances are found. This:

liquid;
plasma;
hard.

If we consider the totality of the planet and space, then most of the substances and bodies are still in the state of gas and plasma. However, the content of solid particles is also significant on the Earth itself. Here we will talk about them, having found out what crystalline and amorphous solids are.

Crystalline and amorphous bodies: a general concept

All solids, bodies, objects are conventionally divided into:

crystalline;
amorphous.

The difference between them is huge, because the subdivision is based on signs of structure and properties. In short, solid crystalline are those substances and bodies that have a certain type of spatial crystal lattice, that is, they have the ability to change in a certain direction, but not in all (anisotropy).

If we characterize amorphous compounds, then their first sign is the ability to change physical characteristics in all directions simultaneously. This is called isotropy.

The structure and properties of crystalline and amorphous bodies are completely different. If the former have a clearly defined structure, consisting of ordered particles in space, then the latter do not have any order.

Properties of solids

Crystalline and amorphous bodies, however, belong to a single group of solids, which means they have all the characteristics of a given state of aggregation. That is, the common properties for them will be the following:

Mechanical - elasticity, hardness, ability to deform.
Thermal - boiling and melting points, coefficient of thermal expansion.
Electrical and magnetic - thermal and electrical conductivity.

Thus, the states we are considering have all these characteristics. Only they will manifest themselves in amorphous bodies somewhat differently than in crystalline ones.

Important properties for industrial purposes are mechanical and electrical. The ability to recover from deformation or, on the contrary, to crumble and grind is an important feature. Also a big role is played by the fact whether a substance can conduct an electric current or is not capable of it.

The structure of crystals

If we describe the structure of crystalline and amorphous bodies, then first of all we should indicate the type of particles that compose them. In the case of crystals, these can be ions, atoms, atom-ions (in metals), molecules (rarely).

In general, these structures are characterized by the presence of a strictly ordered spatial lattice, which is formed as a result of the arrangement of the particles that form the substance. If we imagine the structure of a crystal figuratively, then we get something like this picture: atoms (or other particles) are arranged from each other at certain distances so that the result is an ideal unit cell of the future crystal lattice. Then this cell is repeated many times, and so the overall structure is formed.

The main feature is that the physical properties in such structures change in parallel, but not in all directions. This phenomenon is called anisotropy. That is, if you act on one part of the crystal, then the other side may not react to it. So, you can grind half a piece of table salt, but the second will remain intact.

Crystal types

It is customary to designate two variants of crystals. The first is single-crystal structures, that is, when the lattice itself is 1. Crystalline and amorphous bodies in this case are completely different in properties. After all, a single crystal is characterized by pure anisotropy. It is the smallest structure, elementary.

If single crystals are repeated many times and combined into one whole, then we are talking about a polycrystal. Then we are not talking about anisotropy, since the orientation of elementary cells violates the general ordered structure. In this regard, polycrystals and amorphous bodies are close to each other in terms of their physical properties.

Metals and their alloys

Crystalline and amorphous bodies are very close to each other. This can be easily verified by taking metals and their alloys as an example. By themselves, they are solids under normal conditions. However, at a certain temperature, they begin to melt and, until complete crystallization occurs, they will remain in a state of a stretching, thick, viscous mass. And this is already an amorphous state of the body.

Therefore, strictly speaking, almost every crystalline substance can become amorphous under certain conditions. Just like the latter, during crystallization, it becomes a solid substance with an ordered spatial structure.

Metals can have different types of spatial structures, the most famous and studied of which are the following:

Simple cubic.
face centered.
Volume centered.

The crystal structure can be based on a prism or a pyramid, and its main part is represented by:

triangle;
parallelogram;
square;
hexagon.

Ideal properties of isotropy have a substance that has a simple regular cubic lattice.

The concept of amorphism

Crystalline and amorphous bodies are quite easy to distinguish externally. After all, the latter can often be confused with viscous liquids. The structure of an amorphous substance is also based on ions, atoms, and molecules. However, they do not form an ordered strict structure, and therefore their properties change in all directions. That is, they are isotropic.

Particles are arranged randomly, randomly. Only sometimes they can form small loci, which still does not affect the overall properties exhibited.

Properties of similar bodies

They are identical to those of crystals. Differences are only in indicators for each specific body. For example, the following characteristic parameters of amorphous bodies can be distinguished:

elasticity;
density;
viscosity;
ductility;
conductivity and semiconductivity.

You can often meet the boundary states of connections. Crystalline and amorphous bodies can pass into a semi-amorphous state.

Also of interest is that feature of the state under consideration, which manifests itself under a sharp external impact. So, if an amorphous body is subjected to a sharp impact or deformation, then it is able to behave like a polycrystal and break into small pieces. However, if you give these parts time, they will soon join together again and go into a viscous fluid state.

This state of compounds does not have a specific temperature at which a phase transition occurs. This process is greatly extended, sometimes even for decades (for example, the decomposition of low-pressure polyethylene).

Examples of amorphous substances

Many examples of such substances can be cited. Let's outline some of the most obvious and frequently encountered.

Chocolate is a typical amorphous substance.
Resins, including phenol-formaldehyde, all plastics.
Amber.
Glass of any composition.
Bitumen.
Tar.
Wax and others.

An amorphous body is formed as a result of very slow crystallization, that is, an increase in the viscosity of the solution with a decrease in temperature. It is often difficult to call such substances solid, they are more likely to be referred to as viscous thick liquids.

A special state have those compounds that, when solidified, do not crystallize at all. They are called glasses, and the state is glassy.

glassy substances

The properties of crystalline and amorphous bodies are similar, as we found out, due to a common origin and a single internal nature. But sometimes they separately consider a special state of substances, called glassy. This is a homogeneous mineral solution that crystallizes and hardens without the formation of spatial lattices. That is, it always remains isotropic in terms of changes in properties.

So, for example, ordinary window glass does not have an exact melting point. It simply, with an increase in this indicator, slowly melts, softens and passes into a liquid state. If the impact is stopped, then the reverse process will begin and solidification will begin, but without crystallization.

Such substances are highly valued, glass today is one of the most common and sought-after building materials around the world.

Like a liquid, but also a shape. They are predominantly in the crystalline state.
crystals- These are solids, the atoms or molecules of which occupy certain, ordered positions in space. Therefore, the crystals have flat faces. For example, a grain of ordinary table salt has flat faces that form right angles with each other ( fig.12.1).

This can be seen when examining the salt with a magnifying glass. And how geometrically correct the shape of a snowflake! It also reflects the geometric correctness of the internal structure of a crystalline solid - ice ( fig.12.2).

Anisotropy of crystals. However, the correct external form is not the only and not even the most important consequence of the ordered structure of the crystal. The main thing is dependence of the physical properties of the crystal on the direction chosen in the crystal.
First of all, the different mechanical strength of the crystals in different directions is striking. For example, a piece of mica easily delaminates in one of the directions into thin plates ( fig.12.3), but breaking it in the direction perpendicular to the plates is much more difficult.

The graphite crystal is also easily stratified in one direction. When you write with a pencil, this delamination occurs continuously and thin layers of graphite remain on the paper. This is because the crystal lattice of graphite has a layered structure. The layers are formed by a number of parallel networks consisting of carbon atoms ( fig.12.4). Atoms are located at the vertices of regular hexagons. The distance between the layers is relatively large - about 2 times greater than the length of the side of the hexagon, so the bonds between the layers are less strong than the bonds within them.

Many crystals conduct heat and electric current differently in different directions. The optical properties of crystals also depend on the direction. So, a quartz crystal refracts light differently depending on the direction of the rays falling on it.
The dependence of physical properties on the direction inside the crystal is called anisotropy. All crystalline bodies are anisotropic.
Single crystals and polycrystals. Metals have a crystalline structure. It is metals that are mainly used at present for the manufacture of tools, various machines and mechanisms.
If we take a relatively large piece of metal, then at first glance its crystalline structure does not manifest itself in any way either in the appearance of this piece or in its physical properties. Metals in their normal state do not exhibit anisotropy.
The point here is that usually the metal consists of a huge number of small crystals fused with each other. Under a microscope or even with a magnifying glass, they are easy to see, especially on a fresh fracture of the metal ( fig.12.5). The properties of each crystal depend on the direction, but the crystals are randomly oriented with respect to each other. As a result, in a volume significantly exceeding the volume of individual crystals, all directions inside the metals are equal and the properties of the metals are the same in all directions.

A solid body made up of many small crystals is called polycrystalline. Single crystals are called single crystals.
By observing great precautions, it is possible to grow a large metal crystal - a single crystal.
Under normal conditions, a polycrystalline body is formed as a result of the fact that the growth of many crystals that has begun continues until they come into contact with each other, forming a single body.
Polycrystals are not limited to metals. A lump of sugar, for example, also has a polycrystalline structure.
Most crystalline bodies are polycrystals, since they consist of many intergrown crystals. Single crystals - single crystals have a regular geometric shape, and their properties are different in different directions (anisotropy).

???
1. Are all crystalline bodies anisotropic?
2. Wood is anisotropic. Is she a crystalline body?
3. Give examples of monocrystalline and polycrystalline bodies not mentioned in the text.

G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics Grade 10

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If you have corrections or suggestions for this lesson,

A solid body is one of the four fundamental states of matter, apart from liquid, gas and plasma. It is characterized by structural rigidity and resistance to changes in shape or volume. Unlike a liquid, a solid object does not flow or take on the shape of the container it is placed in. A solid does not expand to fill its available volume, as a gas does.
Atoms in a solid are closely related to each other, are in an ordered state at the nodes of the crystal lattice (these are metals, ordinary ice, sugar, salt, diamond), or are arranged irregularly, do not have strict repeatability in the structure of the crystal lattice (these are amorphous bodies, such like window glass, rosin, mica or plastic).

Crystalline bodies

Crystalline solids or crystals have a distinctive internal feature - a structure in the form of a crystal lattice in which atoms, molecules or ions of a substance occupy a certain position.
The crystal lattice leads to the existence of special flat faces in crystals that distinguish one substance from another. When exposed to X-rays, each crystal lattice emits a characteristic pattern that can be used to identify a substance. The faces of crystals intersect at certain angles that distinguish one substance from another. If the crystal is split, then the new faces will intersect at the same angles as the original one.

They have two characteristic properties: isotropy and the absence of a specific melting point.
The isotropy of amorphous bodies is understood as the sameness of the physical properties of a substance in all directions.
In an amorphous solid, the distance to neighboring nodes of the crystal lattice and the number of neighboring nodes varies throughout the material. Therefore, to break intermolecular interactions, a different amount of thermal energy is required. Consequently, amorphous substances soften slowly over a wide temperature range and do not have a clear melting point.
A feature of amorphous solids is that at low temperatures they have the properties of solids, and with increasing temperature - the properties of liquids.

Crystalline and amorphous bodies

The purpose of the lesson:

To reveal the main properties of crystalline and amorphous bodies.

To introduce students to the correct shape of crystals and the property of anisotropy, a modeling method in the study of the properties of crystals.

Equipment:

A set of crystalline bodies; short focus lens.

Spirit lamp, glass rod.

Computer with multimedia projector; lesson plan, multimedia application for the lesson, made in Mikrosoft Point.

During the classes

Introduction: Most of the solids around us are substances in a crystalline state. These include building and construction materials: various grades of steel, various metal alloys, minerals, etc. A special area of physics - solid state physics - deals with the study of the structure and properties of solids. This area of physics is leading in all physical research. It is the foundation of modern technology.

In any branch of technology, the properties of a solid body are used: mechanical, thermal, electrical, optical, etc. Crystals are increasingly used in technology. You probably know about the merits of Soviet scientists - academicians, laureates of the Lenin and Nobel Prizes A. M. Prokhorov and N. G. Basov in the creation of quantum generators. The action of modern optical quantum generators - lasers - is based on the use of the properties of single crystals (ruby, etc.) How is a crystal arranged? Why do many crystals have amazing properties? What are the structural features of crystals that distinguish them from amorphous bodies? You can answer these and similar questions at the end of the lesson. Let's write down the topic “Crystalline and amorphous bodies”.

Presentation of new material:

Let's go back to the material. What properties do solids have?

Student:

1) They retain their shape and volume.

2) In the structure they have a crystal lattice.

Teacher: All solids are divided into crystalline and amorphous. We will look at their similarities and differences.

What are crystals?

crystals - these are solid bodies, the atoms or molecules of which occupy certain, ordered positions in space. Crystals of the same substance have a variety of shapes. The angles between the individual faces of the crystals are the same. Some crystal shapes are symmetrical. The color of the crystals is different - obviously, it depends on the impurities.

For a visual representation of the internal structure of a crystal, its image is used with the help of a crystal lattice. There are several types of crystals:

1) ionic

2) atomic

3) metal

4) molecular.

The ideal shape of a crystal has the form of a polyhedron. Such a crystal is limited by flat faces, straight edges and has symmetry. In crystals, you can find various elements of symmetry. Crystalline bodies are divided into single crystals and polycrystals.

single crystals - single crystals (quartz, mica...) The ideal shape of a crystal is polyhedral. Such a crystal is limited by flat faces, straight edges and has symmetry. In crystals, you can find various elements of symmetry. Plane of symmetry, axis of symmetry, center of symmetry. At first glance, it seems that the number of types of symmetry can be infinitely large. In 1867, the Russian engineer A. V. Gadolin proved for the first time that crystals can have only 32 types of symmetry. Make sure the symmetry of the snow crystal - snowflakes

The symmetry of crystals and their other properties, which we will discuss below, led to an important guess about the regularities in the arrangement of particles that make up a crystal. Can any of you try to formulate it?

Student. Particles in a crystal are arranged in such a way that they form a certain regular shape, a lattice.

Teacher. Particles in a crystal form a regular spatial lattice. The spatial lattices of different crystals are different. Here is a model of the spatial lattice of table salt. (Demonstrates a model.) Balls of one color imitate sodium ions, balls of a different color imitate chlorine ions. If you connect these nodes with straight lines, then a spatial lattice is formed, similar to the presented model. In each spatial lattice, some repeating elements of its structure can be distinguished, in other words, an elementary cell.

The concept of a spatial lattice made it possible to explain the properties of crystals.

Let's consider their properties.

1) External regular geometric shape (models)

2) Constant melting temperature.

3) Anisotropy - the difference in physical properties from the direction chosen in the crystal (shows an example with mica, with a quartz crystal)

But single crystals are rare in nature. But such a crystal can be grown in artificial conditions.

Now let's get acquainted with polycrystals.

Polycrystals - these are solids consisting of a large number of crystals randomly oriented relative to each other (steel, cast iron ...)

Polycrystals also have a regular shape and even edges, their melting point has a constant value for each substance. But unlike single crystals, polycrystals are isotropic, i.e. physical properties are the same in all directions. This is explained by the fact that the crystals inside are arranged randomly, and each individually has anisotropy, while the crystal as a whole is isotropic.

In addition to crystalline bodies, there are amorphous bodies.

Amorphous bodies - these are solids where only short-range order in the arrangement of atoms is preserved. (Silica, resin, glass, rosin, sugar candy).

For example, quartz can be both in a crystalline state and in an amorphous state - silica. (See the pic in the textbook). They do not have a constant melting point and are fluid (indicates bending a glass rod over a spirit lamp). Amorphous bodies are isotropic, at low temperatures they behave like crystalline bodies, and at high temperatures they are like liquids.

Observation of crystalline and amorphous bodies

(make notes in notebook)

Examine salt crystals with a magnifying glass. - What shape do they have? (cube shape).

Consider the crystals of copper sulphate. – What is the peculiarity of these crystals? (some have flat edges).

Consider a fracture of zinc and find on it the faces of small crystals.

Consider amorphous bodies: glass, rosin or wax. Let's take a look at the broken glass. What is the difference from metal fracture? (smooth surface with sharp edges).

Tasks for independent work.

1. Why does snow creak underfoot in cold weather?

Answer : Hundreds of thousands of snowflakes - crystals break.

2. What is the origin of patterns on the surface of galvanized iron?

Answer : Patterns appear due to crystallization of zinc.

3. Final test.

Teacher: Open your diaries and write down your homework: § 75,76(1); § 24, 26,27. Task for those who wish: to grow crystals from a solution of copper sulphate or alum.

Literature:

1. Myakishev G.Ya., Bukhovtsev B.B., Sotsky N.N. Physics 10 cells. - M .: Education 1992.

2. Pinsky A.A. Physics 10 cells. - M. "Enlightenment" 1993.

3. Tarasov L. V. This amazingly symmetrical world. - M.: Enlightenment, 1982.

4. Schoolchildren about modern physics: physics of complex systems. - M.: Enlightenment, 1978.

5. Encyclopedic dictionary of a young physicist.

6. V.G. Razumovsky, L.S. Khizhnyakov. Modern physics lesson in high school. – M.: Enlightenment, 1983.

7. Methods of teaching physics in grades 8–10 of secondary school. Part 2 / Ed. V.P. Orekhova, A.V. Usova and others - M .: Education 1980.

8. V.A.Volkov. Pourochnye development in physics. M. "VAKO" 2006

Final test

1. Complete the sentence.

1) single crystals;

2) polycrystals.

a) single crystals;

1) a grain of salt;

3) a grain of sugar;

4) a piece of refined sugar

c) amorphous state.

1) crystalline bodies;

2) amorphous bodies.

Final test

1. Complete the sentence.

“The dependence of physical properties on the direction inside the crystal is called…”

2. Fill in the missing words.

"Solid bodies are subdivided into ... and ..."

3. Find a correspondence between solids and crystals.