A solid is one of the four fundamental states of matter other than 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 the shape of the container in which it is placed. A solid does not expand to fill the entire available volume as a gas does.
Atoms in solid body closely connected to each other, are in an ordered state in nodes 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 as window glass, rosin, mica or plastic).
Crystal 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, which distinguish one substance from another. When exposed to X-rays, each crystal lattice emits a characteristic pattern that can be used to identify the substance. The edges of crystals intersect at certain angles that distinguish one substance from another. If the crystal is split, the new faces will intersect at the same angles as the original.
For example, galena - galena, pyrite - pyrite, quartz - quartz. The crystal faces intersect at right angles in galena (PbS) and pyrite (FeS 2), and at other angles in quartz.
Properties of crystals
- constant volume;
- correct geometric shape;
- anisotropy - the difference in mechanical, light, electrical and thermal properties from the direction in the crystal;
- a well-defined melting point, since it depends on the regularity of the crystal lattice. Intermolecular forces holding solid together, are homogeneous, and it takes the same amount of thermal energy to break each interaction simultaneously.
Amorphous bodies
Examples amorphous bodies that do not have a strict structure and repeatability of crystal lattice cells are: glass, resin, Teflon, polyurethane, naphthalene, polyvinyl chloride.
They have two characteristic properties: isotropy and lack of a specific melting point.
Isotropy of amorphous bodies is understood as the same 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, it is required different quantity thermal energy. Hence, amorphous substances soften slowly over a wide temperature range and do not have a clear melting point.
A feature of amorphous solids is that when low temperatures they have the properties of solids, and with increasing temperature - the properties of liquids.
MINISTRY OF EDUCATION
PHYSICS 8TH GRADE
Report on the topic:
“Amorphous bodies. Melting of amorphous bodies.”
8th grade student:
2009
Amorphous bodies.
Let's do an experiment. We will need a piece of plasticine, a stearin candle and an electric fireplace. Let's put plasticine and a candle on equal distances from the fireplace. After some time, part of the stearin will melt (become liquid), and part will remain in the form of a solid piece. During the same time, the plasticine will soften only a little. After some time, all the stearin will melt, and the plasticine will gradually “corrode” along the surface of the table, softening more and more.
So, there are bodies that do not soften when melted, but from solid state turns immediately into liquid. During the melting of such bodies, it is always possible to separate the liquid from the not yet melted (solid) part of the body. These bodies are crystalline. There are also solids that, when heated, gradually soften and become more and more fluid. For such bodies it is impossible to indicate the temperature at which they turn into liquid (melt). These bodies are called amorphous.
Let's do the following experiment. Throw a piece of resin or wax into a glass funnel and leave it in a warm room. After about a month, it will turn out that the wax has taken the shape of a funnel and even began to flow out of it in the form of a “stream” (Fig. 1). In contrast to crystals, which retain almost forever own form, amorphous bodies exhibit fluidity even at low temperatures. Therefore, they can be considered as very thick and viscous liquids.
The structure of amorphous bodies. Studies using an electron microscope, as well as using X-rays, indicate that in amorphous bodies there is no strict order in the arrangement of their particles. Take a look, figure 2 shows the arrangement of particles in crystalline quartz, and the one on the right shows the arrangement of particles in amorphous quartz. These substances consist of the same particles - molecules of silicon oxide SiO 2.
The crystalline state of quartz is obtained if molten quartz is cooled slowly. If the cooling of the melt is rapid, then the molecules will not have time to “line up” in orderly rows, and the result will be amorphous quartz.
Particles of amorphous bodies oscillate continuously and randomly. They can jump from place to place more often than crystal particles. This is also facilitated by the fact that the particles of amorphous bodies are located unequally densely: there are voids between them.
Crystallization of amorphous bodies. Over time (several months, years), amorphous substances spontaneously transform into a crystalline state. For example, sugar candies or fresh honey left alone in a warm place will become opaque after a few months. They say that honey and candy are “candied.” By breaking a candy cane or scooping up honey with a spoon, we will actually see the sugar crystals that have formed.
Spontaneous crystallization of amorphous bodies indicates that the crystalline state of a substance is more stable than the amorphous one. The intermolecular theory explains it this way. Intermolecular forces of attraction and repulsion cause particles of an amorphous body to jump preferentially to where there are voids. As a result, a more ordered arrangement of particles appears than before, that is, a polycrystal is formed.
Melting of amorphous bodies.
As the temperature increases, the energy of the vibrational motion of atoms in a solid increases and, finally, a moment comes when the bonds between atoms begin to break. In this case, the solid turns into a liquid state. This transition is called melting. At a fixed pressure, melting occurs at a strictly defined temperature.
The amount of heat required to convert a unit mass of a substance into a liquid at its melting point is called specific heat melting λ .
To melt a substance of mass m it is necessary to expend an amount of heat equal to:
Q = λ m .
The process of melting amorphous bodies differs from melting crystalline bodies. As the temperature increases, amorphous bodies gradually soften and become viscous until they turn into liquid. Amorphous bodies, unlike crystals, do not have a specific melting point. The temperature of amorphous bodies changes continuously. This happens because in amorphous solids, as in liquids, molecules can move relative to each other. When heated, their speed increases, and the distance between them increases. As a result, the body becomes softer and softer until it turns into liquid. When amorphous bodies solidify, their temperature also decreases continuously.
Along with crystalline solids, amorphous solids are also found. Amorphous bodies, unlike crystals, do not have a strict order in the arrangement of atoms. Only the closest atoms - neighbors - are arranged in some order. But
There is no strict repeatability in all directions of the same structural element, which is characteristic of crystals, in amorphous bodies.
Often the same substance can be found in both crystalline and amorphous state. For example, quartz can be in either crystalline or amorphous form (silica). The crystalline form of quartz can be schematically represented as a lattice of regular hexagons(Fig. 77, a). The amorphous structure of quartz also has the form of a lattice, but irregular shape. Along with hexagons, it contains pentagons and heptagons (Fig. 77, b).
Properties of amorphous bodies. All amorphous bodies are isotropic: their physical properties the same in all directions. Amorphous bodies include glass, many plastics, resin, rosin, sugar candy, etc.
At external influences amorphous bodies exhibit both elastic properties, like solids, and fluidity, like liquids. Under short-term impacts (impacts), they behave like a solid body and, with a strong impact, break into pieces. But at very prolonged exposure amorphous bodies flow. For example, a piece of resin gradually spreads over a solid surface. Atoms or molecules of amorphous bodies, like liquid molecules, have certain time“sedentary life” is the time of oscillations around the equilibrium position. But unlike liquids, this time is very long. In this respect, amorphous bodies are close to crystalline ones, since jumps of atoms from one equilibrium position to another rarely occur.
At low temperatures, amorphous bodies resemble solids in their properties. They have almost no fluidity, but as the temperature rises they gradually soften and their properties become closer and closer to the properties of liquids. This happens because with increasing temperature, jumps of atoms from one position gradually become more frequent.
balance to another. No certain temperature Amorphous bodies, unlike crystalline ones, do not melt.
Solid state physics. All properties of solids (crystalline and amorphous) can be explained on the basis of knowledge of their atomic-molecular structure and the laws of motion of molecules, atoms, ions and electrons that make up solids. Studies of the properties of solids are combined into large area modern physics- solid state physics. The development of solid state physics is stimulated mainly by the needs of technology. Approximately half of the world's physicists work in the field of solid state physics. Of course, achievements in this area are unthinkable without deep knowledge all other branches of physics.
1. How do crystalline bodies differ from amorphous ones? 2. What is anisotropy? 3. Give examples of monocrystalline, polycrystalline and amorphous bodies. 4. How do edge dislocations differ from screw dislocations?
MINISTRY OF EDUCATION
PHYSICS 8TH GRADE
Report on the topic:
“Amorphous bodies. Melting of amorphous bodies.”
8th grade student:
2009
Amorphous bodies.
Let's do an experiment. We will need a piece of plasticine, a stearin candle and an electric fireplace. Let's place plasticine and a candle at equal distances from the fireplace. After some time, part of the stearin will melt (become liquid), and part will remain in the form of a solid piece. During the same time, the plasticine will soften only a little. After some time, all the stearin will melt, and the plasticine will gradually “corrode” along the surface of the table, softening more and more.
So, there are bodies that do not soften when melted, but turn from a solid state immediately into a liquid. During the melting of such bodies, it is always possible to separate the liquid from the not yet melted (solid) part of the body. These bodies are crystalline. There are also solids that, when heated, gradually soften and become more and more fluid. For such bodies it is impossible to indicate the temperature at which they turn into liquid (melt). These bodies are called amorphous.
Let's do the following experiment. Throw a piece of resin or wax into a glass funnel and leave it in a warm room. After about a month, it will turn out that the wax has taken the shape of a funnel and even began to flow out of it in the form of a “stream” (Fig. 1). In contrast to crystals, which retain their own shape almost forever, amorphous bodies exhibit fluidity even at low temperatures. Therefore, they can be considered as very thick and viscous liquids.
The structure of amorphous bodies. Studies using an electron microscope, as well as using X-rays, indicate that in amorphous bodies there is no strict order in the arrangement of their particles. Take a look, figure 2 shows the arrangement of particles in crystalline quartz, and the one on the right shows the arrangement of particles in amorphous quartz. These substances consist of the same particles - molecules of silicon oxide SiO 2.
The crystalline state of quartz is obtained if molten quartz is cooled slowly. If the cooling of the melt is rapid, then the molecules will not have time to “line up” in orderly rows, and the result will be amorphous quartz.
Particles of amorphous bodies oscillate continuously and randomly. They can jump from place to place more often than crystal particles. This is also facilitated by the fact that the particles of amorphous bodies are located unequally densely: there are voids between them.
Crystallization of amorphous bodies. Over time (several months, years), amorphous substances spontaneously transform into a crystalline state. For example, sugar candies or fresh honey left alone in a warm place will become opaque after a few months. They say that honey and candy are “candied.” By breaking a candy cane or scooping up honey with a spoon, we will actually see the sugar crystals that have formed.
Spontaneous crystallization of amorphous bodies indicates that the crystalline state of a substance is more stable than the amorphous one. The intermolecular theory explains it this way. Intermolecular forces of attraction and repulsion cause particles of an amorphous body to jump preferentially to where there are voids. As a result, a more ordered arrangement of particles appears than before, that is, a polycrystal is formed.
Melting of amorphous bodies.
As temperature increases, energy oscillatory motion of atoms in a solid increases and, finally, a moment comes when the bonds between atoms begin to break. In this case, the solid body goes into liquid state. This transition is called melting. At a fixed pressure, melting occurs at a strictly defined temperature.
The amount of heat required to convert a unit mass of a substance into a liquid at its melting point is called the specific heat of fusion λ .
To melt a substance of mass m it is necessary to expend an amount of heat equal to:
Q = λ m .
The process of melting amorphous bodies differs from the melting of crystalline bodies. As the temperature increases, amorphous bodies gradually soften and become viscous until they turn into liquid. Amorphous bodies, unlike crystals, do not have a specific melting point. The temperature of amorphous bodies changes continuously. This happens because in amorphous solids, as in liquids, molecules can move relative to each other. When heated, their speed increases, and the distance between them increases. As a result, the body becomes softer and softer until it turns into liquid. When amorphous bodies solidify, their temperature also decreases continuously.
In the previous paragraph, we learned that some solids (for example, salt, quartz, metals and others) are mono- or polycrystals. Let's get acquainted now with amorphous bodies. They occupy an intermediate position between crystals and liquids, so they cannot be unambiguously called solid.
Let's do an experiment. We will need: a piece of plasticine, a stearin candle and an electric heater. Let's place the plasticine and the candle at equal distances from the heater. Soon part of the candle will melt, part will remain in the form solid, and the plasticine will “go limp.” After some time, all the stearin will melt, and the plasticine will gradually “dissolve”, becoming completely soft.
Like stearin, there are others crystalline substances , which do not soften when heated, and during melting you can always see both the liquid and the part of the body that has not yet melted. This, for example, is all metals. But there are also amorphous substances, which when heated gradually soften and become more and more fluid, so it is impossible to indicate the temperature at which the body turns into liquid (melts).
Amorphous bodies at any temperature have fluidity. Let us confirm this with experience. Let's throw a piece of an amorphous substance into a glass funnel and leave it in a warm room (in the picture - tar resin; asphalt is made from it). After a few weeks, it turns out that the resin took the shape of a funnel and even began to flow out of it like a “jet.” That is an amorphous body behaves like a very thick and viscous liquid.
The structure of amorphous bodies. Electron microscope studies and x-rays show that in amorphous bodies there is no strict order in the arrangement of their particles. Unlike crystals, where there is long range order in the arrangement of particles, in the structure of amorphous bodies, only close order– a certain ordering of the arrangement of particles is preserved only near each individual particle(see picture). The top shows the arrangement of particles in crystalline quartz, the bottom shows the amorphous form of quartz. These substances consist of the same particles - molecules of silicon oxide SiO 2.
Like particles of any bodies, particles of amorphous bodies fluctuate continuously and randomly and, more often than particles of crystals, can jump from place to place. This is facilitated by the fact that the particles of amorphous bodies are located unequally densely, in some places creating relatively large gaps. However, this is not the same as “vacancies” in crystals (see § 7th).
Crystallization of amorphous bodies. Over time (weeks, months), amorphous substances spontaneously transform into a crystalline state. For example, sugar candies or honey left alone for several months become opaque. In this case, the honey and candy are said to be “candied.” By breaking such a candy or scooping up such honey with a spoon, we will see the formation of sugar crystals that previously existed in an amorphous state.
Spontaneous crystallization of amorphous bodies indicates that The crystalline state of a substance is more stable than the amorphous one. MKT explains it this way. The forces of attraction and repulsion of “neighbors” move particles of an amorphous body into situations where potential energy minimal(see § 7-d). In this case, a more ordered arrangement of particles appears, which means that independent crystallization occurs.