A solid is a state of aggregation of a substance, characterized by constancy of shape and the nature of the movement of atoms, which perform small vibrations around equilibrium positions.
In the absence of external influences, a solid body retains its shape and volume.
This is explained by the fact that the attraction between atoms (or molecules) is greater than that of liquids (and especially gases). It is sufficient to keep the atoms near their equilibrium positions.
The molecules or atoms of most solids, such as ice, salt, diamond, and metals, are arranged in a certain order. Such solids are called crystalline . Although the particles of these bodies are in motion, these movements represent oscillations around certain points (equilibrium positions). The particles cannot move far from these points, so the solid retains its shape and volume.
In addition, unlike liquids, the equilibrium points of atoms or ions of a solid body, being connected, are located at the vertices of a regular spatial lattice, which is called crystalline.
The equilibrium positions relative to which thermal vibrations of particles occur are called nodes of the crystal lattice.
Monocrystal- a solid body whose particles form a single crystal lattice (single crystal).
One of the main properties of single crystals, which distinguishes them from liquids and gases, is anisotropy their physical properties. Under anisotropy refers to the dependence of physical properties on direction in a crystal . Anisotropic are mechanical properties (for example, it is known that mica is easy to exfoliate in one direction and very difficult in a perpendicular one), electrical properties (the electrical conductivity of many crystals depends on the direction), optical properties (the phenomenon of birefringence, and dichroism - anisotropy of absorption; so, for example, a single crystal of tourmaline is “painted” in different colors - green and brown, depending on which side you look at it from).
Polycrystal- a solid consisting of randomly oriented single crystals. Most of the solids we deal with in everyday life are polycrystalline - salt, sugar, various metal products. The random orientation of the fused microcrystals of which they consist leads to the disappearance of the anisotropy of properties.
Crystalline bodies have a certain melting point.
Amorphous bodies. In addition to crystalline bodies, amorphous bodies are also classified as solids. Amorphous means “shapeless” in Greek.
Amorphous bodies- these are solid bodies that are characterized by a disordered arrangement of particles in space.
In these bodies, molecules (or atoms) vibrate around randomly located points and, like liquid molecules, have a certain settled life time. But, unlike liquids, this time is very long.
Amorphous bodies include glass, amber, various other resins, and plastics. Although at room temperature these bodies retain their shape, but as the temperature rises they gradually soften and begin to flow like liquids: Amorphous bodies do not have a certain temperature or melting point.
In this they differ from crystalline bodies, which, with increasing temperature, do not gradually, but abruptly, transform into a liquid state (at a very specific temperature - melting point).
All amorphous bodies isotropic, i.e., they have the same physical properties in different directions. When impacted, they behave like solid bodies - they split, and if exposed for a very long time, they flow.
Currently, there are many substances in an amorphous state obtained artificially, for example, amorphous and glassy semiconductors, magnetic materials and even metals.
2. Dispersion of light. Types of spectra. Spectrograph and spectroscope. Spectral analysis. Types of electromagnetic radiation and their application in railway transport.
A ray of white light passing through a triangular prism is not only deflected, but also decomposed into component colored rays.
This phenomenon was discovered by Isaac Newton through a series of experiments.
Newton's experiments
Experience in decomposing white light into a spectrum:
Newton directed the beam sunlight through a small hole onto a glass prism.
When hitting the prism, the beam was refracted and on the opposite wall gave an elongated image with a rainbow alternation of colors - a spectrum.
Newton placed red glass in the path of the sun's ray, behind which he received monochromatic light (red), then a prism and observed on the screen only the red spot from the light ray.
First, Newton directed a ray of sunlight onto a prism. Then, having collected the colored rays emerging from the prism using a collecting lens, Newton received a white image of a hole on a white wall instead of a colored stripe.
Newton's conclusions:
A prism does not change light, but only decomposes it into components
- light rays that differ in color differ in the degree of refraction; Violet rays are refracted most strongly, red ones less strongly.
- red light, which refracts less, has the highest speed, and violet light has the lowest, which is why the prism decomposes the light.
The dependence of the refractive index of light on its color is called dispersion.
White light spectrum:
Conclusions:
- a prism decomposes light
- white light is complex (composite)
- violet rays are refracted more strongly than red ones.
The color of a light beam is determined by its vibration frequency.
When moving from one medium to another, the speed of light and wavelength change, but the frequency that determines the color remains constant.
White light is a collection of waves with lengths from 380 to 760 nm.
The eye perceives rays of a certain wavelength reflected from an object and thus perceives the color of the object.
| Emission spectra The set of frequencies (or wavelengths) contained in the radiation of a substance is called emission spectrum. They come in three types. |
| Solid is a spectrum containing all wavelengths of a certain range from red with λ ≈ 7.6. 10 -7 m to purple with λ ≈ 4. 10 -7 m. A continuous spectrum is emitted by heated solid and liquid substances, gases heated under high pressure. |
| Line spectrum is a spectrum emitted by gases and low-density vapors in the atomic state. Consists of separate lines different color(wavelengths, frequencies) having different locations. Each atom emits a set electromagnetic waves certain frequencies. Therefore everyone chemical element has its own spectrum |
| Banded is the spectrum that is emitted by a gas in its molecular state. |
| Line and stripe spectra can be obtained by heating a substance or passing an electric current. |
| Absorption spectra Absorption spectra are obtained by transmitting light from a source. giving a continuous spectrum through a substance whose atoms are in an unexcited state. The absorption spectrum is the set of frequencies absorbed by a given substance . |
| According to Kirchhoff's law, a substance absorbs those lines of the spectrum that it emits, being a source of light. |
| Spectral analysis The study of emission and absorption spectra allows one to establish the qualitative composition of a substance. The quantitative content of an element in a compound is determined by measuring the brightness of the spectral lines. The method of determining the qualitative and quantitative composition of a substance from its spectrum is called spectroscopy. tral analysis. Knowing the wavelengths emitted by various vapors, it is possible to establish the presence of certain elements in a substance. This method is very sensitive. Individual lines in the spectra of different elements may coincide, but in general the spectrum of each element is its individual characteristic. Spectral analysis has played a big role in science. With its help, the composition of the Sun and stars was studied. Fraunhofer dark lines were discovered in the spectrum of the Sun (1814). The sun is a hot ball of gas ( T≈ 6000 °C), emitting a continuous spectrum. The sun's rays pass through the solar atmosphere, where T ≈ 2000-3000 °C. The corona absorbs certain frequencies from the continuous spectrum, and we on Earth receive the solar absorption spectrum. It can be used to determine which elements are present in the corona of the Sun. He helped discover all the earth's elements, as well as an unknown element called helium. 26 years later (1894) helium was discovered on Earth. Thanks to spectral analysis, 25 elements were discovered. Due to its comparative simplicity and versatility, spectral analysis is the main method for monitoring the composition of a substance in metallurgy and mechanical engineering. Spectral analysis is used to determine chemical composition ores and minerals, Spectral analysis can be performed using both emission and absorption spectra. The composition of complex mixtures is analyzed using a molecular spectrum. |
Range electromagnetic radiation in order of increasing frequency are: 1) Low frequency waves; 2) Radio waves; 3) Infrared radiation; 4) Light radiation; 5) X-ray radiation; 6) Gamma radiation.
All these waves have common properties: absorption, reflection, interference, diffraction, dispersion. These properties can, however, manifest themselves in different ways. The sources and receivers of waves are different.
Radio waves: ν =10 5 - 10 11 Hz, λ =10 -3 -10 3 m.
Obtained using oscillatory circuits and macroscopic vibrators. Properties. Radio waves of different frequencies and wavelengths are absorbed and reflected differently by media. Application Radio communications, television, radar.
Models of the structure of gases, liquids and solids
All substances can exist in three states of aggregation.
Gas– a state of aggregation in which a 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 a characteristic property - anisotropy - the dependence of physical properties on the choice of direction in the crystal.
Lesson No. 2/5 2
Topic No. 26: “Model of the structure of liquid. Saturated and unsaturated pairs. Air humidity."
1 Liquid structure model
Liquid one of states of matter. The main property of a liquid, which distinguishes it from other states of aggregation, is the ability to change its shape indefinitely under the influence of tangential mechanical stresses, even arbitrarily small, while practically maintaining its volume.
Fig.1
The liquid state is usually considered intermediate between solid and gas : a gas retains neither volume nor shape, but a solid retains both.
Molecules liquids do not have a definite position, but at the same time they do not have complete freedom of movement. There is an attraction between them, strong enough to keep them close.
A substance in a liquid state exists in a certain range temperatures , below which it turns intosolid state(crystallization occurs or transformation into a solid amorphous state glass), above into gaseous (evaporation occurs). The boundaries of this interval depend on pressure
All liquids are usually divided into pure liquids and mixtures . Some liquid mixtures have great importance for life: blood, sea water etc. Liquids can perform the function solvents
The main property of liquids is fluidity. If you apply to a section of liquid that is in equilibrium external force , then a flow of liquid particles arises in the direction in which this force is applied: the liquid flows. Thus, under the influence of unbalanced external forces, the liquid does not retain its shape and relative arrangement of parts, and therefore takes the shape of the vessel in which it is located.
Unlike plastic solids, liquids do not haveyield strength: it is enough to apply an arbitrarily small external force to make the liquid flow.
One of characteristic properties liquid is what it has a certain volume ( under constant external conditions). Liquid is extremely difficult to compress mechanically because, unlike gas , there is very little free space between the molecules. The pressure exerted on a liquid enclosed in a vessel is transmitted without change to each point in the volume of this liquid ( Pascal's law , is also valid for gases). This feature, along with very low compressibility, is used in hydraulic machines.
Liquids generally increase in volume (expand) when heated and decrease in volume (contract) when cooled. However, there are exceptions, for example, water shrinks when heated, at normal pressure and at temperatures from 0 °C to approximately 4 °C.
In addition, liquids (like gases) are characterized viscosity . It is defined as the ability to resist the movement of one part relative to another, that is, as internal friction.
When adjacent layers of liquid move relative to each other, collisions of molecules inevitably occur in addition to that caused bythermal movement. Forces arise that inhibit orderly movement. In this case, the kinetic energy of ordered motion transforms into thermal energy of chaotic motion of molecules.
The liquid in the vessel, set in motion and left to its own devices, will gradually stop, but its temperature will increase.In a vapor, like a gas, one can almost ignore the adhesion forces and consider the movement as the free flight of molecules and their collision with each other and with surrounding bodies (walls and liquid covering the bottom of the vessel). In a liquid, molecules, as in a solid, interact strongly, holding each other. However, while in a solid body each molecule retains a certain equilibrium position inside the body indefinitely and its movement is reduced to oscillation around this equilibrium position, the nature of movement in a liquid is different. Liquid molecules move much more freely than solid molecules, although not as freely as gas molecules. Each molecule in a liquid moves here and there for some time, without moving away, however, from its neighbors. This movement resembles the vibration of a solid molecule around its equilibrium position. However, from time to time, a liquid molecule escapes from its environment and moves to another place, ending up in a new environment, where it again performs a motion similar to vibration for some time.
Thus, the movement of liquid molecules is something like a mixture of movements in a solid and in a gas: “oscillatory” movement in one place is replaced by a “free” transition from one place to another. In accordance with this, the structure of a liquid is something between the structure of a solid and the structure of a gas. The higher the temperature, i.e., the greater the kinetic energy of liquid molecules, the greater the role played by “free” movement: the shorter the intervals of the “vibrational” state of the molecule and the more often “free” transitions, i.e., the more the liquid becomes like a gas. At a sufficiently high temperature characteristic of each liquid (the so-called critical temperature), the properties of the liquid do not differ from the properties of a highly compressed gas.
2 Saturated and unsaturated pairs and their properties
There are always vapors of this liquid above the free surface of a liquid. If the vessel with the liquid is not closed, then the concentration of vapor particles at a constant temperature can vary within wide limits, down and up.
Evaporation process in a confined space(closed container with liquid)can occur at a given temperature only up to a certain limit. This is explained by the fact that condensation of steam occurs simultaneously with the evaporation of the liquid. First, the number of molecules leaving the liquid in 1 s is more number molecules returning back, and the density, and therefore the vapor pressure, increases. This leads to an increase in the rate of condensation. After some time, dynamic equilibrium occurs, in which the vapor density above the liquid becomes constant.
Vapor that is in a state of dynamic equilibrium with its liquid is called saturated vapor. Vapor that is not in a state of dynamic equilibrium with its liquid is called unsaturated.
Experience shows that unsaturated pairs obey all gas laws , and the more accurately, the further they are from saturation. Saturated vapors are characterized by the following properties:
- density and pressure of saturated steam at a given temperature these are the maximum density and pressure that steam can have at a given temperature;
- The density and pressure of saturated vapor depend on the type of substance. The lower the specific heat of vaporization of a liquid, the faster it evaporates and the greater the pressure and density of its vapor;
- the pressure and density of saturated steam are uniquely determined by its temperature (do not depend on how the steam reached this temperature: during heating or cooling);
- pressure and vapor density increase rapidly with increasing temperature (Fig. 1, a, b).
Experience shows that when a liquid is heated, the liquid level in a closed vessel decreases. Consequently, the mass and density of the vapor increase. A stronger increase in the pressure of saturated vapor compared to an ideal gas (Gay-Lussac’s law is not applicable to saturated vapor) is explained by the fact that here the pressure increases not only due to an increase in the average kinetic energy of the molecules (as in an ideal gas), but also due to increasing the concentration of molecules;
- at constant temperature, the pressure and density of saturated vapor do not depend on volume. For comparison, Figure 2 shows the isotherms of an ideal gas (a) and saturated vapor (b).
Rice. 2
Experience shows that during isothermal expansion the liquid level in the vessel decreases, and during compression it increases, i.e. the number of vapor molecules changes so that the vapor density remains constant.
3 Humidity
Air containing water vapor is called wet . To characterize the water vapor content in the air, a number of quantities are introduced: absolute humidity, water vapor pressure and relative humidity.
Absolute humidityρ air is a quantity numerically equal to the mass of water vapor contained in 1 m 3 air (i.e. the density of water vapor in the air under given conditions).
Water vapor pressure p is the partial pressure of water vapor contained in the air. The SI units of absolute humidity and elasticity are respectively kilogram per cubic meter (kg/m 3) and pascal (Pa).
If only absolute humidity or water vapor pressure is known, it is still impossible to judge how dry or humid the air is. To determine the degree of air humidity, you need to know whether water vapor is close or far from saturation.
Relative humidity air φ is the ratio of absolute humidity to density expressed as a percentageρ 0 saturated steam at a given temperature (or the ratio of water vapor pressure to pressure p 0 saturated steam at a given temperature):
The lower the relative humidity, the further the steam is from saturation, the more intense evaporation occurs. Saturated steam pressure p 0 at a given temperature table value. Water vapor pressure (and therefore absolute humidity) is determined by the dew point.
When isobarically cooled to a temperature t p the steam becomes saturated and its state is represented by a dot IN . Temperature tp , at which water vapor becomes saturated is called dew point . When cooling below the dew point, vapor condensation begins: fog appears, dew falls, and windows fog up.
4 Air humidity measurement
Measuring instruments are used to measure air humidity hygrometers. There are several types of hygrometers, but the main ones are: hair and psychrometric.
Since it is difficult to directly measure the pressure of water vapor in the air, relative humidity is measuredindirectly.
Operating principlehair hygrometerbased on the property of defatted hair (human or animal)change your lengthdepending on the humidity of the air in which it is located.
Hair stretched over a metal frame. The change in hair length is transmitted to the arrow moving along the scale. In winter, a hair hygrometer is the main instrument for measuring outdoor air humidity.
A more accurate hygrometer is a psychrometric hygrometer psychrometer
(in other Greek “psychros” means cold).
It is known that the relative humidity of the air depends evaporation rate.
The lower the air humidity, the easier it is for moisture to evaporate.
The psychrometer has two thermometers . One is ordinary, they call it dry It measures the ambient air temperature. The bulb of another thermometer is wrapped in a fabric wick and placed in a container of water. The second thermometer does not show the air temperature, but the temperature of the wet wick, hence the name moisturized thermometer. The lower the air humidity, the more intense moisture evaporates from the wick, the greater the amount of heat per unit time is removed from the moistened thermometer, the lower its readings, therefore, the greater the difference between the readings of the dry and moistened thermometers.
The dew point is determined using hygrometers. The condensation hygrometer is a metal box A , front wall TO which is well polished (Fig. 2) An easily evaporating liquid ether is poured inside the box and a thermometer is inserted. Passing air through the box using a rubber bulb G , cause strong evaporation of ether and rapid cooling of the box. The thermometer measures the temperature at which dew droplets appear on the polished surface of the wall. TO . The pressure in the area adjacent to the wall can be considered constant, since this area communicates with the atmosphere and the decrease in pressure due to cooling is compensated by an increase in vapor concentration. The appearance of dew indicates that the water vapor has become saturated. Knowing the air temperature and dew point, you can find the partial pressure of water vapor and relative humidity.
Rice. 2
5 Problems to solve independently
Problem 1
It's cold autumn rain outside. In what case will laundry hanging in the kitchen dry faster: when the window is open or when it is closed? Why?
Problem 2
Air humidity is 78%, and the dry bulb reading is 12 °C. What temperature does the wet bulb thermometer show?(Answer: 10 °C.)
Problem 3
The difference in the readings of dry and wet thermometers is 4 °C. Relative humidity 60%. What are the dry and wet bulb readings?(Answer: t c -l9 °С, t m = 10 °С.)
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 the 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.
1. There are many natural phenomena that can only be understood by knowing the structure of matter. Such phenomena include, for example, the processes of heating and cooling bodies, the transformation of matter from a solid state into a liquid and gaseous state, the formation of fog, etc.
The question of what structure substances have has occupied people since ancient times. So, in the 5th century. BC. The ancient Greek thinker Democritus expressed the idea that matter consists of tiny particles invisible to the eye. He believed that there was a limit to the division of matter. He called this last indivisible particle, which retains the properties of matter, an “atom.” Democritus also believed that atoms are constantly moving and that substances differ in the number of atoms, their sizes, shapes, and order of arrangement.
The guess of ancient thinkers did not immediately turn into a scientific idea. She had many opponents: Aristotle, in particular, believed that the body could be divided indefinitely. The validity of this or that hypothesis could only be confirmed by experience; it was impossible to implement it at that time. Therefore, the ideas of Democritus were forgotten for some time. They returned to them during the Renaissance. In the XVII-XVIII centuries. the properties of gases were studied, and then in the 19th century. a theory of the structure of matter in the gaseous state was constructed. A great contribution to the development of the theory of the structure of matter was made by the Russian scientist M.V. Lomonosov (1711 -1765), who believed that matter consists of atoms, and, using these ideas, was able to explain phenomena such as evaporation, thermal conductivity, etc.
2. The molecular kinetic theory of the structure of matter is based on three principles.
Position 1. All substances are made up of particles with spaces between them. Such particles can be molecules, atoms, ions.
The proof of this position is provided by the facts established during observations and experiments. Such facts include the compressibility of bodies, the solubility of substances in water, etc. So, if you dissolve a little paint in water, the water will become colored. If a drop of this water is placed in another glass with clean water, then this water will also become colored, only its color will be less saturated. You can repeat this operation several more times. In each case, the solution will be colored, only weaker than in the previous one. This means that a drop of paint is divided into particles. The presented facts and the described experience allow us to conclude that bodies are not solid, they consist of small particles.
The fact that bodies are not solid, but that there are gaps between the particles of which they consist, is evidenced by the fact that gas in a cylinder can be compressed by a piston, air can be compressed into hot-air balloon, eraser or piece of rubber, the bodies contract when cooled and expand when heated. Thus, an unheated ball passes freely through a ring whose diameter is slightly larger than the diameter of the ball. If the ball is heated in the flame of an alcohol lamp, it will not fit into the ring.
3. From the experiments discussed above, it follows that a substance can be divided into separate particles that retain its properties. However, there is a certain limit for the division of matter, i.e. there is the smallest particle of a substance that retains its properties. A smaller particle that retains the properties of a given substance simply does not exist.
The smallest particle of a substance that preserves it Chemical properties, is called a molecule.
The words "chemical properties" mean the following. Table salt is a substance that is a compound of sodium and chlorine (NaCl). This compound has certain chemical properties, in particular, it can react with any other substance. In this case, both the salt crystal and the molecule of this chemical compound will behave in the same way in the reaction. In this sense, they say that a molecule retains the chemical properties of a given substance.
4. The experiments that have been described indicate that the molecules are small in size. It is impossible to see them with the naked eye. The diameter of large molecules is approximately 10 -8 cm.
Since molecules are so small, bodies contain a lot of them. So, 1 cm 3 of air contains 27·10 18 molecules.
The mass of molecules, as well as its size, is very small. For example, the mass of one hydrogen molecule is 3.3·10 -24 g or 3.3·10 -27 kg, and the mass of one water molecule is 3·10 -26 kg. The mass of molecules of the same substance is the same. Currently, the mass and size of molecules of various substances are determined quite accurately.
5. Molecules are made up of even smaller particles called atoms. For example, a water molecule can be divided into hydrogen and oxygen. However, hydrogen and oxygen are different substances, and they have properties different from those of water. You can decompose a water molecule into such substances in the process chemical reaction.
An atom is the smallest particle of matter that does not fission during chemical reactions.
A water molecule consists of two hydrogen atoms and one oxygen atom; a molecule of table salt is made up of one sodium atom and one chlorine atom. The sugar molecule is more complex: it consists of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms, and the protein molecule consists of thousands of atoms.
There are substances whose molecules contain homogeneous atoms. For example, a hydrogen molecule consists of two hydrogen atoms, an oxygen molecule - of two oxygen atoms.
There are substances in nature that consist not of molecules, but of atoms. They are called simple. Examples of such substances include aluminum, iron, mercury, tin, etc.
Any substance, regardless of how it is obtained, contains the same atoms. For example, a molecule of water obtained by melting ice, or from the juice of berries, or poured from a tap, contains two hydrogen atoms and one oxygen atom. An oxygen molecule, extracted from atmospheric air or obtained during any chemical reaction, contains two oxygen atoms.
6. Position 2. Molecules are in continuous random (chaotic) motion. Since molecules are small, it is impossible to directly observe and prove their movement. However whole line experimental facts and observed phenomena are a consequence of the movement of molecules. These include primarily Brownian motion and diffusion.
7. Position 3. Molecules interact with each other; forces of attraction and repulsion act between them.
Observations show that bodies do not break down into individual molecules. Hard bodies, such as a wooden stick or a metal rod, are difficult to stretch or break. They are also difficult to compress. It is not easy to compress the liquid in the container. Gases are easier to compress, but you still need to apply some effort to do this.
If bodies do not disintegrate into molecules, then it is obvious that molecules attract each other. Mutual attraction holds molecules near each other.
If you take two lead cylinders and press them together and then release them, they will separate. If the surfaces of the cylinders are cleaned and pressed against each other again, the cylinders will “stick together.” They will not separate even if a load weighing several kilograms is suspended from the lower cylinder. This result can be explained as follows: the cylinders are held together because attractive forces act between the molecules.
Before the cylinders were cleaned, they were separated because the surfaces of the cylinders had irregularities that were removed during cleaning. The surfaces became smooth, and this led to a decrease in the distances between the molecules located on the surfaces of the cylinders when they were pressed against each other. Hence, attractive forces between molecules act over short distances. These distances are approximately equal to the size of the molecule. That is why you cannot break a cup and put the pieces together to get a whole cup. You cannot break a stick into two parts and put them together to get a whole stick.
Along with attractive forces, repulsive forces act between molecules, which prevent the molecules from approaching each other. This explains the fact that bodies are difficult to compress; a compressed spring takes its original shape after the action on it ceases external force. This happens because when compressed, the molecules move closer together and the repulsive forces acting between them increase. They bring the spring to its original state.
When the body is stretched, the repulsive force decreases by to a greater extent than the force of gravity. When a body is compressed, the repulsive force increases to a greater extent than the attractive force.
8. Substances can be in three states of aggregation: solid, liquid and gaseous. The properties of bodies in different states of aggregation are different.
So, a solid body has a certain shape and a certain volume. It is difficult to compress or stretch; if you squeeze it and then release it, it usually restores its shape and volume. The exception is some substances, the solid state of which is close in its properties to liquids (plasticine, wax, var).
The liquid takes the shape of the container into which it is poured. This suggests that liquid under Earth conditions does not have its own shape. Only very small drops of liquid have their own shape - the shape of a ball.
It is extremely difficult to change the volume of liquid. So, if you fill the pump with water, close the hole at the bottom and try to compress the water, it is unlikely to succeed. This means that the liquid has its own volume.
Unlike a liquid, the volume of a gas can be changed quite easily. This can be done by squeezing the ball with your hands or balloon. Gas has no volume of its own; it occupies the entire volume of the container in which it is located. The same can be said about the form of gas.
Thus, solids have their own shape and volume, liquids have their own volume, but do not have own form, gases have neither their own volume nor their own shape. Solids and liquids are difficult to compress, gases are easily compressed.
These properties of bodies can be explained using knowledge about the structure of matter.
Since gases occupy the entire volume provided to them, it is obvious that the attractive forces between gas molecules are small. This means that the molecules are located at relatively large distances from each other. On average, they are tens of times greater than the distances between liquid molecules. This is confirmed by the fact that gases are easily compressible.
Small attractive forces also affect the nature of the movement of gas molecules. A gas molecule moves in a straight line until it collides with another molecule, as a result of which it changes the direction of its motion and moves in a straight line until the next collision.
Solids are difficult to compress. This is due to the fact that the molecules are close to each other and with a slight change in the distance between them, the repulsive forces increase sharply. The relatively large attraction between the molecules of solids leads to the fact that they retain their shape and volume.
The atoms or molecules of most solids are arranged in a certain order and form crystal lattice. Figure 63 shows the crystal lattice of table salt. At the nodes of the crystal lattice there are atoms of sodium (Na) and chlorine (Cl). Particles of a solid body (atoms or molecules) undergo oscillatory motion relative to a node of the crystal lattice.
In liquids, the molecules are also located quite close to each other. Therefore, they are difficult to compress and have their own volume. However, the attractive forces between the molecules of a liquid are not strong enough for the liquid to retain its shape.
The nature of the movement of liquid molecules is very complex. They are not arranged as orderly as the molecules of solids, but in a greater order than the molecules of gases. Liquid molecules undergo oscillatory motion relative to equilibrium positions, but over time these equilibrium positions shift.
Figure 64 shows the arrangement of water molecules in different states of aggregation: solid (c), liquid (b), gaseous (a).
Part 1
1. The molecule is
1) the smallest particle of matter
2) a particle of a substance that retains its chemical properties
3) the smallest particle of a substance that retains all its properties
4) the smallest particle of a substance that retains its chemical properties
2. The fact that there are gaps between particles of a substance is indicated by:
A. Compressibility of gases
B. Dividing a substance into parts
Correct answer
1) only A
2) only B
3) both A and B
4) neither A nor B
3. When heating a column of water in a kettle
1) the average distance between water molecules decreases
2) the average distance between water molecules increases
3) the volume of water molecules increases
4) the volume of water molecules decreases
4. When stretching copper wire between molecules
1) only attractive forces act
2) both attractive and repulsive forces act, but the attractive forces are greater than the repulsive forces
3) both attractive and repulsive forces act, but the repulsive forces are greater than the attractive forces
4) only repulsive forces act
5. A solid elastic body was compressed and a load was placed on it. How have the interaction forces between the molecules of the substance of this body changed?
1) only the forces of attraction have increased
2) only the repulsive forces increased
3) both the attractive and repulsive forces increased, but the attractive forces became greater than the repulsive forces
4) both the attractive and repulsive forces increased, but the repulsive forces became greater than the attractive forces
6. What state of aggregation is a substance in if it does not have its own shape, but has its own volume?
1) only in liquid
2) only in gaseous
3) in liquid or gaseous
4) only in solid
7. What state of aggregation is a substance in if it has neither its own shape nor its own volume?
1) only in liquid
2) only in gaseous
3) in liquid or gaseous
4) only in solid
8. The least order in the arrangement of particles is characteristic of
1) gases
2) liquids
3) crystalline bodies
4) amorphous bodies
9. During the transition of water from a liquid to a crystalline state
1) the distance between molecules increases
2) molecules begin to attract each other
3) orderliness in the arrangement of molecules increases
4) the distance between molecules decreases
10. When the candy transforms from an amorphous state to a crystalline state, sugar crystals form on its surface. Wherein
1) the distances between sugar molecules increase significantly
2) sugar molecules stop moving chaotically
3) orderliness in the arrangement of sugar molecules increases
4) the distances between sugar molecules are significantly reduced
11. From the list of statements below, select two correct ones and write their numbers in the table.
1) A molecule is the smallest particle of a substance.
2) The transfer of pressure by liquid and gas is due to the mobility of their molecules.
3) In an undeformed body, the attractive forces between molecules are equal to the repulsive forces.
4) At small distances between molecules, only repulsive forces act.
5) The interaction between molecules is of a gravitational nature.
12. From the given statements, select two correct ones and write their numbers in the table.
1) When water is poured from one vessel to another, it takes the shape of the vessel.
2) Diffusion in liquids occurs faster than in gases.
3) The molecules of a substance are in continuous directed motion.
4) At a given temperature, all molecules move at the same speeds.
5) Water spreads over a wooden table, since the interaction forces between water molecules are less than the interaction forces between water and wood molecules.
Answers
