Models of the structure of gases, liquids and solids
All substances can exist in three states of aggregation.
Gas – physical state, in which the substance does not have a definite volume and shape. In gases, particles of a substance are removed at distances significantly exceeding the particle size. The attractive forces between particles are small and cannot hold them near each other. The potential energy of particle interaction is considered equal to zero, that is, it is much less than the kinetic energy of particle motion. The particles scatter chaotically, occupying the entire volume of the vessel in which the gas is located. The trajectories of gas particles are broken lines(from one impact to another the particle moves uniformly and rectilinearly). Gases are easily compressed.
Liquid- a state of aggregation in which a substance has a certain volume, but does not retain its shape. In liquids, the distances between particles are comparable to the particle sizes, therefore the interaction forces between particles in liquids are large. The potential energy of particle interaction is comparable to their kinetic energy. But this is not enough for an ordered arrangement of particles. In liquids, only the mutual orientation of neighboring particles is observed. Particles of liquids perform chaotic oscillations around certain equilibrium positions and after some time change places with their neighbors. These jumps explain the fluidity of liquids.
Solid– a state of aggregation in which a substance has a certain volume and retains its shape. In solids, the distances between particles are comparable to the particle sizes, but smaller than in liquids, so the interaction forces between particles are enormous, which allows the substance to maintain its shape. The potential energy of interaction of particles is greater than their kinetic energy, therefore in solids there is an ordered arrangement of particles, called a crystal lattice. Particles of solids undergo chaotic oscillations around the equilibrium position (crystal lattice node) and very rarely change places with their neighbors. Crystals have characteristic property– anisotropy – the dependence of physical properties on the choice of direction in the crystal.
The structure of gases, liquids and solids.
Basic principles of molecular kinetic theory:
All substances are made up of molecules, and molecules are made up of atoms,
atoms and molecules are in constant motion,
There are forces of attraction and repulsion between molecules.
IN gases molecules move chaotically, the distances between molecules are large, molecular forces are small, the gas occupies the entire volume provided to it.
IN liquids molecules are arranged in an orderly manner only at short distances, and at large distances the order (symmetry) of the arrangement is violated - “short-range order”. The forces of molecular attraction keep molecules close together. The movement of molecules is “jumping” from one stable position to another (usually within one layer. This movement explains the fluidity of a liquid. A liquid has no shape, but has volume.
Solids are substances that retain their shape, divided into crystalline and amorphous. Crystalline solids bodies have a crystal lattice, in the nodes of which there may be ions, molecules or atoms. They oscillate relative to stable equilibrium positions.. Crystal lattices have a regular structure throughout the entire volume - “long-range order” of arrangement.
Amorphous bodies retain their shape, but do not have a crystal lattice and, as a result, do not have a pronounced melting point. They are called frozen liquids, since they, like liquids, have a “short-range” order of molecular arrangement.
Molecular interaction forces
All molecules of a substance interact with each other through forces of attraction and repulsion. Evidence of the interaction of molecules: the phenomenon of wetting, resistance to compression and tension, low compressibility of solids and gases, etc. The reason for the interaction of molecules is the electromagnetic interactions of charged particles in a substance. How to explain this? An atom consists of a positively charged nucleus and a negatively charged electron shell. The charge of the nucleus is equal to the total charge of all the electrons, so the atom as a whole is electrically neutral. A molecule consisting of one or more atoms is also electrically neutral. Let's consider the interaction between molecules using the example of two stationary molecules. Gravitational and electromagnetic forces can exist between bodies in nature. Since the masses of molecules are extremely small, negligible forces of gravitational interaction between molecules can be ignored. At very large distances there is also no electromagnetic interaction between molecules. But, as the distance between molecules decreases, the molecules begin to orient themselves in such a way that their sides facing each other will have charges of different signs (in general, the molecules remain neutral), and attractive forces arise between the molecules. With an even greater decrease in the distance between molecules, repulsive forces arise as a result of the interaction of negatively charged electron shells of the atoms of the molecules. As a result, the molecule is acted upon by the sum of the forces of attraction and repulsion. At large distances, the force of attraction predominates (at a distance of 2-3 diameters of the molecule, attraction is maximum), at short distances the force of repulsion prevails. There is a distance between molecules at which the attractive forces become equal to the repulsive forces. This position of the molecules is called the position of stable equilibrium. Molecules located at a distance from each other and connected by electromagnetic forces have potential energy. In a stable equilibrium position, the potential energy of the molecules is minimal. In a substance, each molecule interacts simultaneously with many neighboring molecules, which also affects the value of the minimum potential energy of the molecules. In addition, all molecules of a substance are in continuous motion, i.e. have kinetic energy. Thus, the structure of a substance and its properties (solid, liquid and gaseous bodies) are determined by the relationship between the minimum potential energy of interaction of molecules and the reserve of kinetic energy of thermal motion of molecules.
Structure and properties of solid, liquid and gaseous bodies
The structure of bodies is explained by the interaction of particles of the body and the nature of their thermal movement.
Solid
Solids have a constant shape and volume and are practically incompressible. The minimum potential energy of interaction of molecules is greater than the kinetic energy of molecules. Strong particle interaction. The thermal motion of molecules in a solid is expressed only by vibrations of particles (atoms, molecules) around a stable equilibrium position.
Due to the large forces of attraction, molecules practically cannot change their position in matter, this explains the invariability of the volume and shape of solids. Most solids have a spatially ordered arrangement of particles that form a regular crystal lattice. Particles of matter (atoms, molecules, ions) are located at the vertices - nodes of the crystal lattice. The nodes of the crystal lattice coincide with the position of stable equilibrium of the particles. Such solids are called crystalline.
Liquid
Liquids have a certain volume, but do not have their own shape; they take the shape of the vessel in which they are located. The minimum potential energy of interaction between molecules is comparable to the kinetic energy of molecules. Weak particle interaction. The thermal motion of molecules in a liquid is expressed by vibrations around a stable equilibrium position within the volume provided to the molecule by its neighbors. Molecules cannot move freely throughout the entire volume of a substance, but transitions of molecules to neighboring places are possible. This explains the fluidity of the liquid and the ability to change its shape.
In liquids, molecules are quite firmly bound to each other by forces of attraction, which explains the invariance of the volume of the liquid. In a liquid, the distance between molecules is approximately equal to the diameter of the molecule. When the distance between molecules decreases (compression of the liquid), the repulsive forces increase sharply, so liquids are incompressible. In terms of their structure and the nature of thermal movement, liquids occupy an intermediate position between solids and gases. Although the difference between a liquid and a gas is much greater than between a liquid and a solid. For example, during melting or crystallization, the volume of a body changes many times less than during evaporation or condensation.
Gases do not have a constant volume and occupy the entire volume of the vessel in which they are located. The minimum potential energy of interaction between molecules is less than the kinetic energy of molecules. Particles of matter practically do not interact. Gases are characterized by complete disorder in the arrangement and movement of molecules.
The distance between gas molecules is many times more sizes molecules. Small attractive forces cannot keep molecules close to each other, so gases can expand without limit. Gases are easily compressed under the influence of external pressure, because the distances between molecules are large, and the interaction forces are negligible. The gas pressure on the walls of the container is created by the impacts of moving gas molecules.
>>Physics: Structure of gaseous, liquid and solid bodies
The molecular kinetic theory makes it possible to understand why a substance can exist in gaseous, liquid and solid states.
Gases. In gases, the distance between atoms or molecules is on average many times greater than the size of the molecules themselves ( Fig.8.5). For example, at atmospheric pressure the volume of a vessel is tens of thousands of times greater than the volume of the molecules in it.
Gases are easily compressed, and the average distance between molecules decreases, but the shape of the molecule does not change ( Fig.8.6).
Molecules move at enormous speeds - hundreds of meters per second - in space. When they collide, they bounce off each other in different directions like billiard balls. The weak attractive forces of gas molecules are not able to hold them near each other. That's why gases can expand unlimitedly. They retain neither shape nor volume.
Numerous impacts of molecules on the walls of the vessel create gas pressure.
Liquids. The molecules of the liquid are located almost close to each other ( Fig.8.7), so a liquid molecule behaves differently than a gas molecule. In liquids, there is so-called short-range order, i.e., the ordered arrangement of molecules is maintained over distances equal to several molecular diameters. A molecule oscillates around its equilibrium position by colliding with neighboring molecules. Only from time to time she makes another “jump”, getting into a new equilibrium position. In this equilibrium position, the repulsive force is equal to the attractive force, i.e., the total interaction force of the molecule is zero. Time settled life water molecules, i.e., the time of its vibrations around one specific equilibrium position at room temperature, is on average 10 -11 s. The time of one oscillation is much less (10 -12 -10 -13 s). With increasing temperature, the residence time of molecules decreases.
The nature of molecular motion in liquids, first established by the Soviet physicist Ya.I. Frenkel, allows us to understand the basic properties of liquids.
Liquid molecules are located directly next to each other. As the volume decreases, the repulsive forces become very large. This explains low compressibility of liquids.
As is known, liquids are fluid, that is, they do not retain their shape. This can be explained this way. The external force does not noticeably change the number of molecular jumps per second. But jumps of molecules from one stationary position to another occur predominantly in the direction of action external force (Fig.8.8). This is why liquid flows and takes the shape of the container.
There is another important difference between liquids and solids. A liquid can be compared to a crowd of people, where individual individuals are restlessly jostling in place, and a solid body is like a slender cohort of the same individuals who, although they do not stand at attention, maintain on average certain distances between themselves. If you connect the centers of the equilibrium positions of atoms or ions of a solid body, you get a regular spatial lattice called crystalline.
Figures 8.9 and 8.10 show the crystal lattices of table salt and diamond. The internal order in the arrangement of atoms in crystals leads to regular external geometric shapes.
Figure 8.11 shows Yakut diamonds.
The gas has a distance l between molecules is much larger than the size of the molecules r 0:" l>>r 0
.
In liquids and solids l≈r 0. The molecules of a liquid are arranged in disorder and from time to time jump from one settled position to another.
Crystalline solids have molecules (or atoms) arranged in a strictly ordered manner.
???
1. Gas is capable of unlimited expansion. Why does the Earth have an atmosphere?
2. How do the trajectories of the molecules of gas, liquid and solid differ? Draw approximate trajectories of molecules of substances in these states.
G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics 10th grade
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All nonliving matter is made up of particles that may behave differently. The structure of gaseous, liquid and solid bodies has its own characteristics. The particles in solids are held together by being very close together, which makes them very strong. In addition, they can maintain a certain shape, since their smallest particles practically do not move, but only vibrate. Molecules in liquids are quite close to each other, but they can move freely, so own form they don't have. Particles in gases move very quickly and there is usually a lot of space around them, which means they can be easily compressed.
Properties and structure of solids
What is the structure and structural features of solids? They consist of particles that are located very close to each other. They cannot move and therefore their shape remains fixed. What are the properties of a solid? It does not compress, but if it is heated, its volume will increase with increasing temperature. This happens because the particles begin to vibrate and move, causing the density to decrease.
One of the characteristics of solids is that they have a constant shape. When a solid heats up, the movement of the particles increases. Faster moving particles collide more violently, causing each particle to push its neighbors. Therefore, an increase in temperature usually results in an increase in the strength of the body.
Crystal structure of solids
The intermolecular forces of interaction between neighboring molecules of a solid are strong enough to keep them in a fixed position. If these smallest particles are in a highly ordered configuration, then such structures are usually called crystalline. Questions of the internal order of particles (atoms, ions, molecules) of an element or compound are dealt with by a special science - crystallography.
Solids are also of particular interest. By studying the behavior of particles and how they are structured, chemists can explain and predict how certain types materials will behave under certain conditions. The smallest particles of a solid are arranged in a lattice. This is the so-called regular arrangement of particles, where various chemical bonds between them.
The band theory of the structure of a solid body considers it as a collection of atoms, each of which, in turn, consists of a nucleus and electrons. In the crystalline structure, the nuclei of atoms are located in the nodes of the crystal lattice, which is characterized by a certain spatial periodicity.
What is the structure of a liquid?
The structure of solids and liquids is similar in that the particles of which they are composed are located at close range. The difference is that the molecules move freely, since the force of attraction between them is much weaker than in a solid body.
What properties does the liquid have? The first is fluidity, and the second is that the liquid will take the shape of the container in which it is placed. If you heat it up, the volume will increase. Due to the close proximity of the particles to each other, the liquid cannot be compressed.
What is the structure and structure of gaseous bodies?
The gas particles are arranged randomly, they are so far from each other that no attractive force can arise between them. What properties does gas have and what is the structure of gaseous bodies? As a rule, the gas evenly fills the entire space in which it was placed. It compresses easily. The speed of particles of a gaseous body increases with increasing temperature. At the same time, pressure also increases.
The structure of gaseous, liquid and solid bodies is characterized by different distances between the smallest particles of these substances. Gas particles are much further apart than solid or liquid particles. In air, for example, the average distance between particles is approximately ten times the diameter of each particle. Thus, the volume of molecules occupies only about 0.1% of the total volume. The remaining 99.9% is empty space. In contrast, liquid particles fill about 70% of the total liquid volume.
Each gas particle moves freely along a straight path until it collides with another particle (gas, liquid or solid). The particles usually move quite quickly, and after two of them collide, they bounce off each other and continue on their way alone. These collisions change direction and speed. These properties of gas particles allow gases to expand to fill any shape or volume.
State change
The structure of gaseous, liquid and solid bodies can change if they are exposed to a certain external influence. They can even transform into each other's states under certain conditions, such as during heating or cooling.
- Evaporation. The structure and properties of liquid bodies allow them, under certain conditions, to transform into a completely different physical state. For example, if you accidentally spill gasoline while refueling your car, you can quickly notice its pungent odor. How does this happen? Particles move throughout the liquid, eventually reaching the surface. Their directed motion can carry these molecules beyond the surface into the space above the liquid, but gravity will pull them back. On the other hand, if a particle moves very quickly, it can become separated from others by a considerable distance. Thus, with an increase in the speed of particles, which usually occurs when heated, the process of evaporation occurs, that is, the conversion of liquid into gas.
Behavior of bodies in different physical states
The structure of gases, liquids, and solids is mainly due to the fact that all these substances consist of atoms, molecules or ions, but the behavior of these particles can be completely different. Gas particles are randomly spaced from each other, liquid molecules are close to each other, but they are not as rigidly structured as in a solid. Gas particles vibrate and move at high speeds. The atoms and molecules of a liquid vibrate, move, and slide past each other. Particles of a solid body can also vibrate, but movement as such is not characteristic of them.
Features of the internal structure
In order to understand the behavior of matter, you must first study the features of its internal structure. What are the internal differences between granite, olive oil and helium in balloon? A simple model of the structure of matter will help answer this question.
A model is a simplified version of a real object or substance. For example, before actual construction begins, architects first construct a model of the construction project. Such a simplified model does not necessarily imply an exact description, but at the same time it can give an approximate idea of what a particular structure will be like.
Simplified models
In science, however, models are not always physical bodies. For last century there has been a significant increase in human understanding about physical world. However, much of the accumulated knowledge and experience is based on extremely complex concepts, such as mathematical, chemical and physical formulas.
In order to understand all this, you need to be quite well versed in these exact and complex sciences. Scientists have developed simplified models to visualize, explain, and predict physical phenomena. All this greatly simplifies the understanding of why some bodies have a constant shape and volume at a certain temperature, while others can change them, and so on.
All matter is made up of tiny particles. These particles are in constant movement. The amount of movement is related to temperature. An increased temperature indicates an increase in movement speed. The structure of gaseous, liquid and solid bodies is distinguished by the freedom of movement of their particles, as well as by how strongly the particles are attracted to each other. Physical depend on his physical condition. Water vapor, liquid water and ice have the same chemical properties, but their physical properties differ significantly.
1. Model of the structure of liquids. Saturated and unsaturated pairs; dependence of saturated vapor pressure on temperature; boiling. Air humidity; dew point, hygrometer, psychrometer.
Evaporation - vaporization that occurs at any temperature from the free surface of a liquid. During thermal motion at any temperature, the kinetic energy of liquid molecules does not significantly exceed the potential energy of their connection with other molecules. Evaporation is accompanied by cooling of the liquid. The rate of evaporation depends on: the open surface area, temperature, and the concentration of molecules near the liquid.
Condensation- the process of transition of a substance from a gaseous state to a liquid state.
The evaporation of a liquid in a closed vessel at a constant temperature leads to a gradual increase in the concentration of molecules of the evaporating substance in the gaseous state. Some time after the start of evaporation, the concentration of the substance in the gaseous state will reach a value at which the number of molecules returning to the liquid becomes equal to the number molecules leaving the liquid during the same time. Installed dynamic equilibrium between the processes of evaporation and condensation of matter.
A substance in a gaseous state that is in dynamic equilibrium with liquid is called saturated steam. (Vapor is the collection of molecules that leave the liquid during the process of evaporation.) Vapor at a pressure below saturated is called unsaturated.
Due to the constant evaporation of water from the surfaces of reservoirs, soil and vegetation, as well as the respiration of humans and animals, the atmosphere always contains water vapor. Therefore, atmospheric pressure is the sum of the pressure of dry air and the water vapor contained in it. The water vapor pressure will be maximum when the air is saturated with steam. Saturated steam, unlike unsaturated steam, does not obey the laws of an ideal gas. Thus, saturated vapor pressure does not depend on volume, but depends on temperature. This dependence cannot be expressed by a simple formula, therefore, based on an experimental study of the dependence of saturated vapor pressure on temperature, tables have been compiled from which its pressure can be determined at different temperatures.
The pressure of water vapor in the air at a given temperature is called absolute humidity. Since vapor pressure is proportional to the concentration of molecules, absolute humidity can be defined as the density of water vapor present in the air at a given temperature, expressed in kilograms per cubic meter (p).
Relative humidity is the ratio of the density of water vapor (or pressure) in the air at a given temperature to the density (or pressure) of water vapor at that the same temperature, expressed as a percentage, i.e.
The most favorable for humans in middle climatic latitudes is a relative humidity of 40-60%.
By lowering the air temperature, the steam in it can be brought to saturation.
dew pointis the temperature at which vapor in the air becomes saturated. When the dew point is reached in the air or on objects with which it comes into contact, water vapor begins to condense. To determine air humidity, instruments called hygrometers and psychrometers are used.