We learn what bodies and substances are; we learn how bodies differ from. What is a substance? What are the classes of substances

In life, we are surrounded by various bodies and objects. For example, indoors it is a window, a door, a table, a light bulb, a cup, on the street - a car, a traffic light, asphalt. Any body or object is made up of matter. This article will discuss what a substance is.

What is chemistry?

Water is an essential solvent and stabilizer. It has strong heat capacity and thermal conductivity. Water environment favorable for the occurrence of basic chemical reactions. It is transparent and practically resistant to compression.

What is the difference between inorganic and organic substances?

Particularly strong external differences there is no difference between these two groups. The main difference lies in the structure, where inorganic substances have a non-molecular structure, and organic substances have a molecular structure.

Inorganic substances have a non-molecular structure, therefore, they are characterized by high melting and boiling points. They do not contain carbon. These include noble gases (neon, argon), metals (calcium, calcium, sodium), amphoteric substances (iron, aluminum) and non-metals (silicon), hydroxides, binary compounds, salts.

Organic substances of molecular structure. They have enough low temperatures melting, and they quickly decompose when heated. Mostly composed of carbon. Exceptions: carbides, carbonates, oxides of carbon and cyanides. Carbon allows the formation of a huge number of complex compounds (more than 10 million are known in nature).

Most of their classes belong to biological origin (carbohydrates, proteins, lipids, nucleic acids). These compounds include nitrogen, hydrogen, oxygen, phosphorus and sulfur.

To understand what a substance is, it is necessary to imagine what role it plays in our life. Interacting with other substances, it forms new ones. Without them, the vital activity of the surrounding world is inseparable and unthinkable. All objects are made up of certain substances, so they play an important role in our lives.

Substances and bodies belong to the material component of reality. Both of them have their own signs. Consider the difference between matter and body.

Definition

Substance called matter that has mass (in contrast, for example, from electromagnetic field) and having a structure of many particles. There are substances consisting of independent atoms, such as aluminum. More often, atoms are combined into more or less complex molecules. Such a molecular substance is polyethylene.

Body- a separate material object having its own boundaries, occupying a part of the surrounding space. The constant characteristics of such an object are mass and volume. Bodies also have specific sizes and shapes, which form a certain visual image of objects. Bodies may already exist in nature or be the result of human creativity. Examples of bodies: a book, an apple, a vase.

Comparison

In general, the difference between a substance and a body is as follows: substance is what existing objects are created from (the internal aspect of matter), and these objects themselves are bodies (the external aspect of matter). So, paraffin is a substance, and a candle from it is a body. It must be said that the body is not the only state in which substances can exist.

Any substance has a set of specific properties due to which it can be distinguished from a number of other substances. Such properties include, for example, features of the crystal structure or the degree of heating at which melting occurs.

By mixing the existing components, you can get completely different substances with their own unique set of properties. There are many substances created by people based on those found in nature. Such artificial products are, for example, nylon and soda. Substances from which something is made by people are called materials.

What is the difference between matter and body? A substance is always homogeneous in composition, that is, all molecules or other individual particles in it are the same. At the same time, the body is not always characterized by uniformity. For example, a jar made of glass is a homogeneous body, but a digging shovel is heterogeneous, since its upper and lower parts are made of different materials.

From certain substances, many different bodies can be made. For example, balls are made from rubber, car tires, rugs. At the same time, bodies that perform the same function can be made of different substances like, say, aluminum and wooden spoons.

In today's article, we will discuss what the physical body is. this term has already met you more than once during the years of schooling. We first encounter the concepts of "physical body", "substance", "phenomenon" in the lessons of natural history. They are the subject of study of most sections of the special science - physics.

According to "physical body" means a certain material object that has a form and a clearly defined outer boundary that separates it from external environment and other bodies. In addition, the physical body has such characteristics as mass and volume. These parameters are basic. But there are others besides them. We are talking about transparency, density, elasticity, hardness, etc.

Physical bodies: examples

To put it simply, we can call any of the surrounding objects a physical body. The most familiar examples of them are a book, a table, a car, a ball, a cup. Physics calls a simple body that whose geometric shape uncomplicated. Composite physical bodies are those that exist in the form of combinations of interconnected simple bodies. For example, a very conditionally human figure can be represented as a set of cylinders and balls.

The material of which any of the bodies consists is called substance. At the same time, they can contain in their composition both one and a number of substances. Let's give examples. physical bodies- cutlery (forks, spoons). They are usually made from steel. A knife can serve as an example of a body consisting of two different types substances - steel blade and wooden handle. And such a complex product as a cell phone is made from a much larger number of "ingredients".

What are the substances

They can be natural or artificially created. In ancient times, people made all the necessary items from natural materials (arrowheads - from clothes - from animal skins). With the development of technological progress, substances created by man appeared. And now they are in the majority. A classic example of a physical body artificial origin can be plastic. Each of its types was created by a person in order to ensure the necessary qualities of a particular object. For example, transparent plastic - for glasses lenses, non-toxic food - for dishes, durable - for car bumpers.

Any object (from to a high-tech device) has a number of certain qualities. One of the properties of physical bodies is their ability to attract each other as a result of gravitational interaction. It is measured using a physical quantity called mass. By definition of physicists, the mass of bodies is a measure of their gravity. It is denoted by the symbol m.

Mass measurement

This physical quantity, like any other, is measurable. To find out what is the mass of any object, you need to compare it with the standard. That is, with a body whose mass is taken as a unit. international system units (SI) it is considered a kilogram. Such an "ideal" unit of mass exists in the form of a cylinder, which is an alloy of iridium and platinum. This international design is kept in France, and copies are available in almost every country.

In addition to kilograms, the concept of tons, grams or milligrams is used. Body weight is measured by weighing. This is a classic way for everyday calculations. But in modern physics there are others that are much more modern and highly accurate. With their help, the mass of microparticles, as well as giant objects, is determined.

Other properties of physical bodies

Shape, mass and volume are the most important characteristics. But there are other properties of physical bodies, each of which is important in a particular situation. For example, objects of equal volume can differ significantly in their mass, that is, have different densities. In many situations, characteristics such as brittleness, hardness, resilience or magnetic qualities are important. We should not forget about thermal conductivity, transparency, uniformity, electrical conductivity and other numerous physical properties bodies and substances.

In most cases, all such characteristics depend on the substances or materials of which the objects are composed. For example, rubber, glass and steel balls will have completely different sets of physical properties. This is important in situations where bodies interact with each other, for example, in studying the degree of their deformation when colliding.

About accepted approximations

Certain sections of physics consider the physical body as a kind of abstraction with ideal characteristics. For example, in mechanics, bodies are represented as material points, having no mass and other properties. This branch of physics deals with the movement of such conditional points, and for solving the problems posed here, such quantities are of no fundamental importance.

In scientific calculations, the concept of absolutely solid body. Such is conditionally considered a body that is not subject to any deformations, with no displacement of the center of mass. This simplified model makes it possible to theoretically reproduce a number of specific processes.

The section of thermodynamics for its own purposes uses the concept of a completely black body. What is it? A physical body (a certain abstract object) capable of absorbing any radiation falling on its surface. At the same time, if the task requires it, they can emit electromagnetic waves. If, according to the conditions of theoretical calculations, the shape of physical bodies is not fundamental, it is considered by default that it is spherical.

Why are the properties of bodies so important?

Physics itself, as such, originated from the need to comprehend the laws by which physical bodies behave, as well as the mechanisms for the existence of various external phenomena. Natural factors include any changes in our environment that are not related to the results of human activity. Many of them are used by people to their advantage, but others can be dangerous and even catastrophic.

The study of the behavior and various properties of physical bodies is necessary for people in order to predict adverse factors and prevent or reduce the harm they cause. For example, by building breakwaters, people are accustomed to dealing with the negative manifestations of the sea. Mankind has learned to resist earthquakes by developing special earthquake-resistant building structures. The load-bearing parts of the car are made in a special, carefully calibrated form to reduce damage in accidents.

About the structure of bodies

According to another definition, the term "physical body" means everything that can be recognized as really existing. Any of them necessarily occupies a part of space, and the substances of which they are composed are a collection of molecules of a certain structure. Others, more small particles his - atoms, but each of them is not something indivisible and completely simple. The structure of an atom is rather complicated. It contains positively and negatively charged elementary particles- ions.

The structure, according to which such particles line up in a certain system, for solids is called crystalline. Any crystal has a certain, strictly fixed shape, which indicates the ordered movement and interaction of its molecules and atoms. When the structure of crystals changes, a violation of the physical properties of the body occurs. The state of aggregation, which can be solid, liquid or gaseous, depends on the degree of mobility of elementary components.

To characterize these complex phenomena, the concept of compression coefficients or volumetric elasticity, which are mutually reciprocal, is used.

Molecule movement

The state of rest is not inherent in either atoms or molecules of solids. They are in constant motion, the nature of which depends on the thermal state of the body, and the influences that it is in. this moment exposed. Part of the elementary particles - negatively charged ions (called electrons) moves at a higher speed than those with a positive charge.

From the point of view of the state of aggregation, physical bodies are hard objects, liquids or gases, depending on the nature of molecular motion. The whole set of solids can be divided into crystalline and amorphous. The motion of particles in a crystal is recognized as completely ordered. In liquids, molecules move according to a completely different principle. They move from one group to another, which can be figuratively represented like comets wandering from one celestial system to another.

In any of the gaseous bodies, the molecules have a much weaker bond than in liquid or solid. Particles there can be called repulsive from each other. The elasticity of physical bodies is determined by a combination of two main quantities - the shear coefficient and the coefficient of volume elasticity.

Body fluidity

Despite all the significant differences between solid and liquid physical bodies, their properties have much in common. Some of them, called soft ones, occupy an intermediate state of aggregation between the first and second ones with physical properties inherent in both. Such a quality as fluidity can be found in a solid body (an example is ice or shoe pitch). It is also inherent in metals, including rather hard ones. Under pressure, most of them are able to flow like a liquid. By joining and heating two solid pieces of metal, it is possible to solder them into a single whole. Moreover, the soldering process takes place at a temperature much lower than the melting point of each of them.

This process is possible provided that both parts are in full contact. It is in this way that various metal alloys are obtained. The corresponding property is called diffusion.

About liquids and gases

Based on the results of numerous experiments, scientists have come to the following conclusion: solid physical bodies are not some isolated group. The difference between them and liquid ones is only in greater internal friction. The transition of substances into different states takes place at a certain temperature.

Gases differ from liquids and solids in that there is no increase in the elastic force even with a strong change in volume. The difference between liquids and solids is in the occurrence of elastic forces in solids during shear, that is, a change in shape. This phenomenon is not observed in liquids, which can take any of the forms.

Crystalline and amorphous

As already mentioned, two possible states of solids are amorphous and crystalline. Amorphous bodies are bodies that have the same physical properties in all directions. This quality is called isotropy. Examples include hardened resin, amber products, glass. Their isotropy is the result of the random arrangement of molecules and atoms in the composition of matter.

In the crystalline state, elementary particles are arranged in a strict order and exist in the form of an internal structure, periodically repeating in different directions. The physical properties of such bodies are different, but in parallel directions they coincide. This property inherent in crystals is called anisotropy. Its reason is the unequal force of interaction between molecules and atoms in different directions.

Mono- and polycrystals

In single crystals, the internal structure is homogeneous and repeats throughout the volume. Polycrystals look like a lot of small crystallites chaotically intergrown with each other. Their constituent particles are located at a strictly defined distance from each other and in the right order. A crystal lattice is understood as a set of nodes, that is, points that serve as centers of molecules or atoms. Metals with a crystalline structure serve as a material for the frames of bridges, buildings and other durable structures. That is why the properties of crystalline bodies are carefully studied for practical purposes.

The actual strength characteristics are negative impact defects crystal lattice both superficial and internal. A separate section of physics, called solid body mechanics, is devoted to similar properties of solids.

Bodies are objects that surround us.

Bodies are made up of substances.

Physical bodies differ in shape, size, have mass, volume.

Matter is what the physical body is made of. The essential property of a substance is its mass.

Material is the substance from which bodies are made.

Define "substance", "material", "body".

What is the difference between "substance" and "body"? Give examples. Why are there more bodies than substances?

Figures and facts

One ton of waste paper can produce 750 kg of paper or 25,000 school notebooks.

20 tons of waste paper save a hectare of forest from cutting down.

inquisitive

In the aviation and space industry, in gas turbines, in plants for the chemical processing of coal, where heat using composite materials. These are materials consisting of a plastic base (matrix) and a filler. Composites include ceramic-metal materials (cermets), norplasts (filled organic polymers). As a matrix, metals and alloys, polymers, and ceramics are used. Composites are much more durable than traditional materials.

home experiment

Chromatography on paper

Mix a drop of blue and red ink (maybe a mixture of water-soluble paints that do not interact with each other). Take a sheet of filter paper, apply a small drop of the mixture to the center of the paper, then water drips into the center of this drop. A color chromatogram will begin to form on the filter paper.

Familiarization with laboratory glassware and chemical equipment

In the process of studying chemistry, many experiments have to be carried out, for which special equipment and utensils are used.

In chemistry, special dishes made of thin-walled and thick-walled glass are used. Products made of thin-walled glass are resistant to temperature extremes; chemical operations that require heating are carried out in them. Thick glassware should not be heated. By appointment, glassware is general purpose, special purpose and measured. General purpose cookware is used for most jobs.

Thin-walled General Purpose Glassware

Test tubes are used when performing experiments with small amounts of solutions or solids, for demonstration experiments. Let's use the utensils to perform the experiments.

Pour into two small test tubes of 1-2 ml. hydrochloric acid solution. In one add 1-2 drops of litmus, and the second - so much methyl orange. We observe the change in the color of the indicators. Litmus turns red and methyl orange turns pink.

Pour into three small test tubes 1-2 ml of sodium hydroxide solution. Add 1-2 drops of litmus to one, the color becomes blue. In the second - the same amount of methyl orange - the color becomes yellow. In the third - phenolphthalein, the color becomes crimson. So, with the help of indicators, you can determine the environment of solutions.

Place a little soda sodium hydrogen carbonate in a large test tube and add 1-2 ml of acetic acid solution. We immediately observe a kind of “boiling” of a mixture of these substances. This impression is created due to the rapid release of bubbles. carbon dioxide. If a lit match is brought into the upper particle of the test tube when gas is released, it goes out without burning out.

Substances are dissolved in flasks, solutions are filtered and titrated. Chemical beakers are used to carry out precipitation reactions, the dissolution of solids when heated. The group of special purpose includes dishes used for a specific purpose. In thick-walled dishes, experiments are performed that do not require heating. Most often, reagents are stored in it. Droppers, funnels, gasometers, Kipp apparatus, glass rods are also made from thick glass.

We dip one glass rod in concentrated p hydrochloric acid, and the second in p ammonia. Let's bring the sticks closer to each other, we observe the formation of "smoke without fire".

In measuring utensils belong pipettes, burettes, flasks, cylinders, beakers, glasses. Measuring utensils accurately determine the volume of liquids, prepare solutions of various concentrations.

In addition to glassware, porcelain dishes are used in the laboratory: cups, crucibles, mortars. Porcelain cups are used to evaporate solutions, and porcelain crucibles are used to calcinate substances in muffle furnaces. Mortars grind solids.

Laboratory equipment

To heat substances in chemical laboratories, alcohol stoves, electric stoves with a closed spiral, water baths, and, in the presence of gas, gas burners are used. You can also use dry fuel, burning it on special stands.

Auxiliary accessories are of great importance when performing chemical experiments: a metal stand, a stand for test tubes, crucible tongs, asbestos mesh.

Scales are used to weigh substances.

1.1. Bodies and environments. Understanding Systems

While studying physics last year, you learned that the world we live in is a world physical bodies and Wednesdays. How is the physical body different from the environment? Any physical body has a shape and volume.

For example, a wide variety of objects are physical bodies: an aluminum spoon, a nail, a diamond, a glass, a plastic bag, an iceberg, a grain of table salt, a lump of sugar, a raindrop. And the air? He is constantly around us, but we do not see his form. For us, air is a medium. Another example: for a person, the sea is, although very large, but still a physical body - it has a shape and volume. And for the fish that swims in it, the sea is most likely the environment.

From my life experience you know that everything that surrounds us consists of something. The textbook that lies before you consists of thin sheets of text and a more durable cover; an alarm clock that wakes you up in the morning - from a variety of different parts. That is, we can say that the textbook and the alarm clock are system.

It is very important that the constituent parts of the system are connected, since in the absence of connections between them, any system would turn into a "heap".

The most important feature of each system is its compound and structure. All other features of the system depend on the composition and structure.

The concept of systems is necessary for us in order to understand what physical bodies and environments consist of, because all of them are systems. (Gas media (gases) form a system only together with what keeps them from expanding.)

BODY, ENVIRONMENT, SYSTEM, COMPOSITION OF THE SYSTEM, STRUCTURE OF THE SYSTEM.
1. Give several examples of physical bodies missing in the textbook (no more than five).
2. What physical environments does a frog face in everyday life?
3. How do you think the physical body differs from the environment?

If you look into a sugar bowl or salt shaker, you will see that sugar and salt are made up of fairly small grains. And if you look at these grains through a magnifying glass, you can see that each of them is a polyhedron with flat edges (crystal). Without special equipment, we will not be able to distinguish what these crystals are made of, but modern science is well aware of methods that allow this to be done. These methods and the devices that use them were developed by physicists. They use very complex phenomena, which we will not consider here. We will only say that these methods can be likened to a very powerful microscope. If we look at a crystal of salt or sugar in such a "microscope" with greater and greater magnification, then, in the end, we will find that very small particles of a spherical shape are part of this crystal. Usually they are called atoms(although this is not entirely true, their more accurate name is nuclides). Atoms are part of all the bodies and environments around us.

Atoms are very small particles, their size ranges from one to five angstroms (denoted - A o .). One angstrom is 10-10 meters. The size of a sugar crystal is approximately 1 mm; such a crystal is approximately 10 million times larger than any of its constituent atoms. To get a better idea of ​​how small particles atoms are, consider this example: if an apple is enlarged to the size the globe, then an atom magnified by the same factor will become the size of an average apple.
Despite their small size, atoms are rather complex particles. You will get acquainted with the structure of atoms this year, but for now we will only say that any atom consists of atomic nucleus and related electron shell, which is also a system.
Just over a hundred types of atoms are currently known. Of these, about eighty are stable. And from these eighty types of atoms, all the objects around us are built in all their infinite variety.
One of key features atoms is their tendency to combine with each other. Most often, this results in molecules.

A molecule can contain from two to several hundred thousand atoms. At the same time, small molecules (diatomic, triatomic ...) can also consist of identical atoms, while large ones, as a rule, consist of different atoms. Since a molecule consists of several atoms and these atoms are connected, the molecule is a system. In solids and liquids, molecules are connected to each other, but in gases they are not.
The bonds between atoms are called chemical bonds, and bonds between molecules intermolecular bonds.
Molecules linked together form substances.

Substances made up of molecules are called molecular substances. So, water is made up of water molecules, sugar is made up of sucrose molecules, and polyethylene is made up of polyethylene molecules.
In addition, many substances are composed directly of atoms or other particles and do not contain molecules in their composition. For example, aluminum, iron, diamond, glass, salt do not contain molecules. Such substances are called non-molecular.

In non-molecular substances, atoms and other chemical particles, as in molecules, are interconnected by chemical bonds. The division of substances into molecular and non-molecular is the classification of substances by building type.
Assuming that interconnected atoms retain a spherical shape, it is possible to construct three-dimensional models of molecules and non-molecular crystals. Examples of such models are shown in Figs. 1.1.
Most substances are usually found in one of three aggregate states: solid, liquid or gaseous. When heated or cooled, molecular substances can pass from one state of aggregation to another. Such transitions are schematically shown in Fig. 1.2.

The transition of a nonmolecular substance from one state of aggregation to another may be accompanied by a change in the type of structure. Most often, this phenomenon occurs during the evaporation of non-molecular substances.

At melting, boiling, condensation and similar phenomena that occur with molecular substances, the molecules of substances are not destroyed and are not formed. Only intermolecular bonds are broken or formed. For example, when ice melts, it turns into water, and when water boils, it turns into water vapour. Water molecules are not destroyed in this case, and, therefore, as a substance, water remains unchanged. Thus, in all three states of aggregation, this is the same substance - water.

But not all molecular substances can exist in all three states of aggregation. Many of them when heated decompose, that is, they are converted into other substances, while their molecules are destroyed. For example, cellulose (the main component of wood and paper) does not melt when heated, but decomposes. Its molecules are destroyed, and completely different molecules are formed from the "fragments".

So, the molecular substance remains itself, that is, chemically unchanged, as long as its molecules remain unchanged.

But you know that molecules are in constant motion. And the atoms that make up molecules also move (oscillate). As the temperature rises, the vibrations of atoms in molecules increase. Can we say that the molecules remain completely unchanged? Of course not! What then remains unchanged? The answer to this question is in one of the following paragraphs.

ATOM (NUCLIDE), MOLECULE, CHEMICAL BOND, INTERMOLECULAR BOND, MOLECULAR SUBSTANCE, NON-MOLECULAR SUBSTANCE, STRUCTURE TYPE, AGGREGATE STATE.

1. What bonds are stronger: chemical or intermolecular?
2. What is the difference between solid, liquid and gaseous states from each other? How do molecules move in gas, liquid and solid?
3. Have you ever observed the melting of any substances (except ice)? What about boiling (other than water)?
4. What are the features of these processes? Give examples of sublimation of solids known to you.
5. Give examples of substances known to you that can be a) in all three states of aggregation; b) only in solid or liquid state; c) only in the solid state.

As you already know, atoms are the same and different. How different atoms differ from each other in structure, you will soon learn, but for now we will only say that different atoms differ chemical behavior, that is, its ability to combine with each other, forming molecules (or non-molecular substances).

In other words, chemical elements are the very types of atoms that were mentioned in the previous paragraph.
Each chemical element has its own name, for example: hydrogen, carbon, iron, and so on. In addition, each element is also assigned its own symbol. You see these symbols, for example, in the "Table of Chemical Elements" in the school chemistry room.
A chemical element is an abstract collection. This is the name of any number of atoms of a given type, and these atoms can be anywhere, for example: one on Earth, and the other on Venus. A chemical element cannot be seen or felt by hand. The atoms that make up a chemical element may or may not be bonded to each other. Consequently, a chemical element is neither a substance nor a material system.

CHEMICAL ELEMENT, ELEMENT SYMBOL.
1. Give a definition of the concept of "chemical element" using the words "type of atoms".
2. How many meanings does the word "iron" have in chemistry? What are these values?

Before proceeding with the classification of any objects, it is necessary to choose the feature by which you will carry out this classification ( classification feature). For example, when putting a pile of pencils into boxes, you can be guided by their color, shape, length, hardness, or something else. The selected characteristic will be the classification feature. Substances are much more complex and diverse objects than pencils, so there are much more classification features here.
All substances (and you already know that matter is a system) are made up of particles. The first classification feature is the presence (or absence) of atomic nuclei in these particles. On this basis, all substances are divided into chemical substances and physical substances.

Such particles (and they are called chemical particles) can be atoms (particles with one nucleus), molecules (particles with several nuclei), non-molecular crystals (particles with many nuclei), and some others. Any chemical particle, in addition to nuclei or nuclei, also contains electrons.
Except chemical substances, there are other substances in nature. For example: the substance of neutron stars, consisting of particles called neutrons; flows of electrons, neutrons and other particles. Such substances are called physical.

On Earth, you almost never encounter physical matter.
According to the type of chemical particles or the type of structure, all chemicals are divided into molecular and non-molecular, you already know that.
A substance can consist of chemical particles of the same composition and structure - in this case it is called clean, or individual substance. If the particles are different, then mixture.

This applies to both molecular and non-molecular substances. For example, the molecular substance "water" consists of water molecules of the same composition and structure, and the non-molecular substance "salt" consists of salt crystals of the same composition and structure.
Most natural substances are mixtures. For example, air is a mixture of molecular substances "nitrogen" and "oxygen" with impurities of other gases, and rock "granite" is a mixture of non-molecular substances "quartz", "feldspar" and "mica" also with various impurities.
Individual chemicals are often referred to simply as substances.
Chemical substances can contain atoms of only one chemical element or atoms of different elements. On this basis, substances are divided into simple and complex.

For example, the simple substance "oxygen" consists of diatomic oxygen molecules, and the composition of the substance "oxygen" includes only atoms of the element oxygen. Another example: the simple substance "iron" consists of iron crystals, and the composition of the substance "iron" includes only atoms of the element iron. Historically, a simple substance usually has the same name as the element whose atoms are part of this substance.
However, some elements form not one, but several simple substances. For example, the element oxygen forms two simple substances: "oxygen", consisting of diatomic molecules, and "ozone", consisting of triatomic molecules. The element carbon forms two well-known non-molecular simple substances: diamond and graphite. Such a phenomenon is called allotropy.

These simple substances are called allotropic modifications. They are identical in quality composition, but differ from each other in structure.

Thus, the complex substance "water" consists of water molecules, which, in turn, consist of hydrogen and oxygen atoms. Therefore, hydrogen atoms and oxygen atoms are part of water. The complex substance "quartz" consists of quartz crystals, quartz crystals consist of silicon atoms and oxygen atoms, that is, silicon atoms and oxygen atoms are part of quartz. Of course, the composition of a complex substance can include atoms and more than two elements.
Compounds are also called compounds.
Examples of simple and complex substances, as well as their type of structure, are shown in Table 1.

Table I. Simple and complex substances molecular (m) and non-molecular (n / m) type of structure

On fig. 1.3 shows a scheme for classifying substances according to the characteristics we have studied: by the presence of nuclei in the particles that form the substance, by the chemical identity of substances, by the content of atoms of one or more elements, and by the type of structure. The scheme is supplemented by dividing mixtures into mechanical mixtures and solutions, here the classification feature is the structural level at which the particles are mixed.

Like individual substances, solutions can be solid, liquid (commonly referred to simply as "solutions"), and gaseous (called mixtures of gases). Examples of solid solutions: gold-silver jewelry alloy, ruby ​​gemstone. Examples of liquid solutions are well known to you: for example, a solution of table salt in water, table vinegar (a solution of acetic acid in water). Examples of gaseous solutions: air, oxygen-helium mixtures for breathing scuba divers, etc.

CHEMICAL SUBSTANCE, INDIVIDUAL SUBSTANCE, MIXTURE, SIMPLE SUBSTANCE, COMPOUND SUBSTANCE, ALLOTROPY, SOLUTION.
1. Give at least three examples of individual substances and the same number of examples of mixtures.
2. What simple substances do you constantly encounter in life?
3. Which of the individual substances you gave as an example are simple substances, and which are complex?
4. In which of the following sentences are we talking about a chemical element, and which ones are about a simple substance?
a) An oxygen atom collided with a carbon atom.
b) Water contains hydrogen and oxygen.
c) A mixture of hydrogen and oxygen is explosive.
d) The most refractory metal is tungsten.
e) The pan is made of aluminum.
f) Quartz is a compound of silicon with oxygen.
g) An oxygen molecule consists of two oxygen atoms.
h) Copper, silver and gold have been known to people since ancient times.
5. Give five examples of solutions you know.
6. What, in your opinion, is the external difference between a mechanical mixture and a solution?

Each of the objects of the material system (except elementary particles) is itself a system, that is, it consists of other, smaller, objects interconnected. So, any system itself is a complex object, and almost all objects are systems. For example, a system important for chemistry - a molecule - consists of atoms linked by chemical bonds (you will learn about the nature of these bonds by studying Chapter 7). Another example: an atom. It is also a material system consisting of an atomic nucleus and electrons associated with it (you will learn about the nature of these bonds by studying Chapter 3).
Each object can be described or characterized in more or less detail, that is, list it characteristics.

In chemistry, objects are, first of all, substances. Chemicals are very diverse: liquid and solid, colorless and colored, light and heavy, active and inert, and so on. One substance differs from another in a number of ways, which, as you know, are called characteristics.

There are a wide variety of characteristics of substances: state of aggregation, color, smell, density, ability to melt, melting point, ability to decompose when heated, decomposition temperature, hygroscopicity (ability to absorb moisture), viscosity, ability to interact with other substances and many others. The most important of these features are compound and structure. It is on the composition and structure of a substance that all its other characteristics, including properties, depend.
Distinguish qualitative composition and quantitative composition substances.
To describe the qualitative composition of a substance, list the atoms of which elements are part of this substance.
When describing the quantitative composition of a molecular substance, the atoms of which elements and in what quantity form a molecule of a given substance.
When describing the quantitative composition of a non-molecular substance, the ratio of the number of atoms of each of the elements that make up this substance is indicated.
The structure of a substance is understood as a) the sequence of interconnection of atoms forming given substance; b) the nature of the bonds between them; and c) the mutual arrangement of atoms in space.
Now let's return to the question that ended paragraph 1.2: what remains unchanged in molecules if the molecular substance remains itself? Now we can already answer this question: their composition and structure remain unchanged in molecules. And if so, then we can clarify the conclusion we made in paragraph 1.2:

A substance remains itself, that is, chemically unchanged, as long as the composition and structure of its molecules remain unchanged (for non-molecular substances - as long as its composition and the nature of the bonds between atoms are preserved ).

As for other systems, among the characteristics of substances in special group stand out properties of substances, that is, their ability to change as a result of interaction with other bodies or substances, as well as as a result of interaction constituent parts of this substance.
The second case is quite rare, so the properties of a substance can be defined as the ability of this substance to change in a certain way under some external influence. And since external influences can be very diverse (heating, compression, immersion in water, mixing with another substance, etc.), they can also cause various changes. When heated, a solid can melt, or it can decompose without melting, turning into other substances. If a substance melts when heated, then we say that it has the ability to melt. This is a property of a given substance (it appears, for example, in silver and is absent in cellulose). Also, when heated, a liquid may boil, or it may not boil, but also decompose. This is the ability to boil (it manifests itself, for example, in water and is absent in molten polyethylene). A substance immersed in water may or may not dissolve in it, this property is the ability to dissolve in water. Paper brought to the fire ignites in air, but gold wire does not, that is, paper (or rather, cellulose) exhibits the ability to burn in air, and gold wire does not have this property. Substances have many different properties.
The ability to melt, the ability to boil, the ability to deform and the like properties refer to physical properties substances.

The ability to react with other substances, the ability to decompose, and sometimes the ability to dissolve, refers to chemical properties substances.

Another group of characteristics of substances - quantitative characteristics. Of the characteristics given at the beginning of the paragraph, density, melting point, decomposition temperature, and viscosity are quantitative. All of them represent physical quantities. In the course of physics, you got acquainted with physical quantities in the seventh grade and continue to study them. The most important physical quantities used in chemistry, you will study in detail this year.
Among the characteristics of a substance, there are those that are neither properties nor quantitative characteristics, but are of great importance in describing the substance. These include the composition, structure, state of aggregation and other characteristics.
Each individual substance has its own set of characteristics, and the quantitative characteristics of such a substance are constant. For example, pure water under normal pressure, it boils at exactly 100 o C, ethyl alcohol boils at 78 o C under the same conditions. Both water and ethyl alcohol are individual substances. And gasoline, for example, being a mixture of several substances, does not have a specific boiling point (it boils in a certain temperature range).

Differences in the physical properties and other characteristics of substances make it possible to separate mixtures consisting of them.

To separate mixtures into their constituent substances, various physical separation methods are used, for example: upholding With decantation(by draining the liquid from the sediment), filtration(straining), evaporation,magnetic separation(separation with a magnet) and many other methods. You will get to know some of these methods practically.

CHARACTERISTICS OF THE SUBSTANCE, QUALITATIVE COMPOSITION, QUANTITATIVE COMPOSITION, STRUCTURE OF THE SUBSTANCE, PROPERTIES OF THE SUBSTANCE, PHYSICAL PROPERTIES, CHEMICAL PROPERTIES.
1. Describe how the system
a) any object well known to you,
b) solar system. Indicate the constituent parts of these systems and the nature of the connections between the constituent parts.
2. Give examples of systems consisting of the same components, but having a different structure
3. List as many characteristics as possible of some household item, for example, a pencil (as a system!). Which of these characteristics are properties?
4. What is a characteristic of a substance? Give examples.
5. What is a property of a substance? Give examples.
6. The following are sets of characteristics of three substances. All these substances are well known to you. Determine what substances are involved
a) A colorless solid with a density of 2.16 g / cm 3 forms transparent cubic crystals, odorless, soluble in water, an aqueous solution has a salty taste, melts when heated to 801 o C, and boils at 1465 o C, in moderate doses for humans is not toxic.
b) An orange-red solid with a density of 8.9 g / cm 3, the crystals are indistinguishable to the eye, the surface is shiny, does not dissolve in water, conducts electric current very well, is plastic (easily drawn into a wire), melts at 1084 o C , and at 2540 o C boils, in the air it gradually becomes covered with a loose pale blue-green bloom.
c) Transparent colorless liquid with a pungent odor, density 1.05 g/cm 3 , miscible with water in all respects, aqueous solutions have sour taste, in dilute aqueous solutions for humans is not poisonous, is used as a seasoning for food, when cooled to -17 o C it hardens, and when heated to 118 o C it boils, corrodes many metals. 7. Which of the characteristics given in the previous three examples are a) physical properties, b) Chemical properties, c) values ​​of physical quantities.
8. Make your own lists of characteristics of two more substances you know.
Separation of substances by filtration.

Everything that happens with the participation of physical objects is called natural phenomena. These include the transitions of substances from one state of aggregation to another, and the decomposition of substances when heated, and their interactions with each other.

During melting, boiling, sublimation, liquid flow, solid body bending and other similar phenomena, the molecules of substances do not change.

And what happens, for example, when burning sulfur?
During the combustion of sulfur, sulfur molecules and oxygen molecules change: they turn into sulfur dioxide molecules (see Fig. 1.4). Please note that and total number atoms, and the number of atoms of each of the elements remains unchanged.
Therefore, there are two types of natural phenomena:
1) phenomena in which the molecules of substances do not change - physical phenomena;
2) phenomena in which the molecules of substances change - chemical phenomena.
What happens to the substances during these phenomena?
In the first case, the molecules collide and fly apart without changing; in the second, the molecules, having collided, react with each other, while some molecules (old) are destroyed, and others (new) are formed.
What changes in molecules during chemical phenomena?
In molecules, atoms are bound by strong chemical bonds into a single particle (in non-molecular substances, into a single crystal). The nature of atoms in chemical phenomena does not change, that is, atoms do not turn into each other. The number of atoms of each element also does not change (atoms do not disappear and do not appear). What is changing? Bonds between atoms! Similarly, in non-molecular substances, chemical phenomena change the bonds between atoms. Changing bonds usually comes down to their breaking and the subsequent formation of new bonds. For example, during the combustion of sulfur in air, the bonds between sulfur atoms in sulfur molecules and between oxygen atoms in oxygen molecules are broken, and bonds are formed between sulfur and oxygen atoms in sulfur dioxide molecules.

The appearance of new substances is detected by the disappearance of the characteristics of the reacting substances and the appearance of new characteristics inherent in the reaction products. So, when sulfur is burned, yellow sulfur powder turns into a gas with a sharp unpleasant odor, and when phosphorus is burned, clouds of white smoke are formed, consisting of the smallest particles of phosphorus oxide.
So, chemical phenomena are accompanied by the breaking and formation of chemical bonds, therefore, chemistry as a science studies natural phenomena in which chemical bonds are broken and formed (chemical reactions), the physical phenomena accompanying them and, of course, the chemicals involved in these reactions.
To study chemical phenomena (that is, chemistry), you must first study the bonds between atoms (what they are, what they are, what are their features). But bonds are formed between atoms. Therefore, it is necessary first of all to study the atoms themselves, more precisely, the structure of atoms of different elements.
So in 8th and 9th grade you will learn
1) the structure of atoms;
2) chemical bonds and structure of substances;
3) chemical reactions and the processes that accompany them;
4) properties of the most important simple substances and compounds.
In addition, during this time you will get acquainted with the most important physical quantities used in chemistry, and with the relationships between them, as well as learn how to perform basic chemical calculations.