Material- the material has some general properties), by which it can be recognized. Its other properties can vary, which makes it possible to distinguish between varieties of the same material. Examples of materials are wood, leather, rubber and brass. Different types of wood have slightly different properties: color, density, hardness. Changing the properties that distinguish one variety of this material from another variety, not much. The chemical composition of the material can also be variable, but its changes are usually minor.

Substance- a substance has properties by which it can be recognized. These properties are constant for all samples of the substance. The chemical composition of the substance is unchanged. Examples of substances are iron, sugar, table salt. Many substances are compounds, some substances are simple substances.

Compound- a substance consisting of two or more elements combined in a certain proportion, which can be decomposed by a chemical reaction into simpler substances. The chemical composition of such a substance is known, and a chemical formula can be assigned to it. For example, lime is a compound of calcium and oxygen, one calcium atom combines with one oxygen atom to form one molecule of lime (calcium oxide), chemical formula of this compound CaO. The difference between the concepts material, substance and the connection is next material(for example, a tree) has chemical composition and properties that can vary within certain limits, a substance (for example, sugar) has a certain chemical composition and properties, but its structure is too complex to describe, a compound (for example, sulfuric acid) has a certain chemical composition, known chemical structure, and a precise chemical formula can be assigned to it.

Simple substance- a substance that cannot be further decomposed by ordinary chemical reactions. Each simple substance consists of atoms of only one element.

Property- that which can be seen, heard, smelled or touched and which allows a material or substance to be recognized and distinguished from other materials or substances All materials and substances have physical properties and chemical properties.

Physical property- a property of a substance that does not depend on the influence of other materials or substances on the latter. Examples of physical properties are shape, color, odor, solubility, melting point, density.

Extensive property- a property that does not depend on the amount of material or substance; such properties are used to identify the material or substance. For example, color, smell, density, boiling point.

Intensive property- a property that depends on the amount of material or substance, such properties are used to identify different samples of the same material or substance. For example, mass, volume

Characteristic (characteristic)- a property that allows you to easily distinguish any object, material, substance, crystallographic motif among all other similar objects. For example, copper has a characteristic reddish-brown color that makes it easy to distinguish from other metals.

Sign- a distinctive property common to any group of materials or substances.

Description- a list of properties of an object, material, substance, crystallographic motif, form of energy, or a list of a set or sequence of events in a process.

Physical state- solid, liquid or gaseous form of existence of a substance. Any substance can be in one of these three physical states.

State change- the physical transformation of a substance, transferring it from one physical state to another, for example from solid to liquid, from liquid to gaseous. The change in state is usually caused by heating or cooling.

Solid (substance)- one of the forms of existence of matter. A solid has a certain volume and a certain shape, which are difficult to change. Preservation of volume and shape is a property of a solid. For example, iron at room temperature is a solid .

Melt- convert a solid into a liquid by heating. For example, heating melts ice; ice melts when heated. Only one substance takes part in this process, in which two or more substances participate.

Molten- the term describes a substance in a liquid state. Such a substance is assumed to be solid at room temperature.

To harden (harden)- convert a liquid into a solid by cooling. Solidification is the opposite process of melting; only one material or substance takes part in this process. This concept applies only to materials and substances that are normally solid at room temperature. For example, molten iron solidifies when cooled to approximately 1500 °C

Grasping- hardening of liquid suspensions as the liquid evaporates and sets.

Freeze (freeze)- convert a liquid into a solid by cooling to below room temperature. This concept applies to substances that are normally liquid at room temperature. For example, water freezes to form ice. Freezing is the opposite process of melting.

Liquid- one of the physical states of matter. A liquid has a definite volume, but no definite shape. It is easy to change the shape of a liquid, but difficult to change the volume. For example, water and kerosene are liquids at room temperature. The liquid takes the shape of the container in which it is placed.

Boil-the term characterizes the transformation of liquid into vapor when heated. Bubbles of steam formed when a liquid boils and bubbles of dissolved air are released from it. During the boiling process, the temperature of the liquid remains constant.

Boiled water is water that has been boiling for some time. Such water no longer contains dissolved air

Liquefy- convert gas into liquid by cooling, liquefaction.

liquefy- convert a solid into a fluid form.

Gas- one of the physical states of matter. Gas does not have a specific volume or shape; they are easy to change. Gas has another special property: it is capable of expanding, filling the entire volume of the vessel in which it is located.

Gaseous (gas)- the term characterizes a substance in the form of a gas or chemical reaction between gases

Steam- a substance in a gaseous state. Steam can be turned into liquid by increasing pressure. Gas is called steam at a temperature below the critical temperature substances. Comparison of gas with steam, both represent the gaseous state of a substance, but above the critical temperature the substance is a gas and cannot be liquefied at any high pressure, and below the critical temperature the substance is a vapor and can be turned into a liquid with a sufficient increase in pressure to evaporate

Evaporate- turn into steam at a temperature below the boiling point of the substance. For example, naphthalene evaporates at room temperature.

Evaporate- turn liquid into steam and in this way gradually reduce the volume of liquid. The essential factor here is the reduction in volume.

Condense- convert steam into liquid by cooling or increasing pressure, or both at the same time; the transformation of steam into liquid as a result of cooling or increasing pressure. This term applies to materials and substances that are liquid at room temperature; the usual method of condensation is by cooling.

Condensation- formation of liquid from its vapor. For example, the condensation of water vapor into liquid water.

Fluid (fluid)- substance in fluid form - liquid or gas flowing

Boiling point- the temperature at which a liquid turns into vapor. At boiling point pressure saturated steam liquid is equal to atmospheric pressure. The lower the atmospheric pressure, the lower the boiling point of the liquid. The boiling point of water at normal atmospheric pressure equal to 100 °C.

Melting point- the temperature at which a solid becomes liquid. At the melting point, solid and liquid forms of a substance exist simultaneously. The melting point of a solid depends slightly on ambient pressure. The term melting point applies to substances that are solid at room temperature.

Freezing point- the temperature at which a liquid substance becomes solid. The term “freezing point” applies to substances that are liquid at room temperature. For example, the freezing point of water is 0 °C, but the melting point of naphthalene is 80 °C.

Weight- a property of a material or substance that causes its attraction to the earth. The force of attraction of an object or any substance to the earth is its weight. Mass is measured in kilograms, weight is measured in newtons.

Volume- the space occupied by an object in three dimensions.

Density- mass of material or substance per unit volume (1 m3). The density for any sample of material or substance is equal to the mass/volume ratio. Density is an extensive property used in identifying materials and substances. Density dimension kg/m3.

Relative density- the density of a material or substance relative to the density of water (divided by it). Relative density is a dimensionless numerical value.

Relative vapor density- the density of a gas or vapor relative to the density of hydrogen (divided by it) at the same temperature and pressure. Relative vapor density is a dimensionless numerical value that does not depend on temperature and pressure. The relative vapor density of any substance is numerically equal to half its molecular weight.

Vapor Density- the same as relative vapor density.

Physical transformation- a transformation in which no new materials or substances are formed. During a physical transformation, a material or substance can change its physical state or any of its physical properties; for example, the change from water to water vapor is a physical transformation.

Grinding degree- size of solid particles. For example, marble may have three different degrees grinding: pieces, crumbs or powder.

Particle- a very small portion of a solid material or substance.

Piece- a separate part of something, such as a large piece of solid material or substance irregular shape lump.

Chit- a small particle of solid material or substance. The crumb is smaller than a piece, but larger than a granule.

Flakes- small flat particles of solid material or substance. The flakes are similar in size to crumbs.

Granule (grain)- a small particle of solid material or substance consisting of several grains.

grain- a very small piece of solid material or substance, particle, visible to the naked eye. Sand and salt consist of grains.

Powder- a solid material or substance consisting of particles so small that they are indistinguishable to the naked eye.

Sawdust- small particles formed when processing the material with a saw or file; they are similar in size to grains or granules, but longer and thinner.

Shavings- thin, narrow particles, cut off with a sharp tool when processing the material, they are much larger than sawdust.

Fine grain- the term characterizes powders or sawdust with a very high degree of grinding.

Coarse grain- the term characterizes powders and sawdust with larger particles than fine-grained ones.

Finely ground- the term characterizes a solid material or substance in the form of a powder with very small particles, i.e. in the form of a fine-grained powder.

Texture- the nature of the surface of a solid material or substance, for example, a rough or smooth surface. The texture of the powder, granules or grains depends on whether the particles are fine or coarse. For example, the surface may have a smooth texture; the powder may have a rough texture.

Massive- the term characterizes a solid material or substance, in particular metal, taken in the form of large pieces. For example, solid zinc is made up of large pieces of zinc. The term massive is used in contrast to the term finely ground.

Elastic (elastic)- the term characterizes a solid material or substance that changes its shape under the influence of an applied force, but restores its original shape after the removal of this force. For example, a piece of rubber is elastic (elastic). This property of such substances is called elasticity .

Plastic- the term characterizes a solid material or substance that changes its shape under the influence of an applied force, but does not restore its original shape after the force ceases. For example, clay is plastic. This property of such substances is called plasticity.

Fragile- the term characterizes a solid material or substance that breaks into small pieces under the influence of applied force. For example, glass is fragile; it shatters into small pieces when struck. This property of such substances is called fragility.

Viscous- the term characterizes a solid material or substance that can be drawn into a thin wire. Metals and alloys are malleable. The specified property of similar solids called ductility.

Malleable- the term describes a solid material or substance that can change its shape into thin sheets when struck with a hammer. For example, iron is malleable. This property of solids is called malleability.

Abrasive- the term characterizes a material that abrades (grinds the surface of another material) .

Fireproof (refractory)- the term characterizes a solid material or substance whose properties do not change when heated to high temperature. For example, some types of bricks are fire-resistant.

Porous- the term characterizes a solid material permeated with very small pores through which fluid substances can pass. For example, brick is porous.

Crystal- the term characterizes a solid material or substance that consists of molecules, atoms or ions arranged in a regular structure. A crystalline substance forms crystals; metals have a crystalline structure, but do not form large crystals.

Amorphous- the term characterizes a solid material or substance that does not have a crystalline structure. Glass, rubber and many plastics are amorphous.

Dyed (colored)- the term characterizes a material or substance that has a color (color), for example, a colored solution can be brown, blue, green, black, etc. The material or substance can be characterized as white or colored. For example, milk is a white liquid, but lead sulfide forms as a black precipitate, which is considered a colored precipitate.

Colorless- the term characterizes a material or substance that has no color (color), for example, water is colorless, air is colorless. Colorless is the opposite in meaning to colored. It is necessary to distinguish white from colorless, the paper of this book is white, and the window glass is colorless

Smell- a property of a material or substance that is recognized by the sense of smell. For example, onions have a very specific smell odorous.

Deprived odor - the term characterizes a material or substance that has no odor.

Quality - essential features, features - properties of a material or substance that cannot be measured quantitatively. For example, color, smell or texture are qualitative properties of materials and substances.

Give- impart a new quality to any object or change quantitative characteristics any object. For example, sugar gives sweet taste tea, potassium salts are added lilac color flame

Surface- the outer part of a solid object; it has length, width and area, but no thickness (depth) and volume. The liquid has a surface at the interface with air. Examples of brick have six surfaces; surface of water in a cup.

Granular (granular)- term 1) characterizes a surface as if consisting of many grains or grains (granules); 2) coarse powder consisting of granules (grains).

Dull (matte)- the term characterizes a surface that weakly reflects the light falling on it. Dull has the opposite meaning of bright. For example, wax has a dull surface.

Shine- the property of a surface to strongly reflect light falling on it. Gloss is a quality property. For example, the surface of silver has a shine.

Transparent- the term characterizes solid object, a material or substance that allows light to pass through, allowing one to see through it. For example, glass is transparent .

Translucent (translucent)- the term characterizes a solid object, material or substance that allows light to pass through it, but does not allow one to see clearly through it. For example, wax paper is translucent, but not transparent, milk is a translucent, translucent liquid.

Opaque- the term characterizes an object, material or substance that does not transmit light through itself. For example, leather and thick paper are opaque, mercury is opaque.

Light- the term characterizes a transparent liquid. For example, water is a light-colored liquid. The light liquid can be colored or colorless. For example, tea is a light brown liquid; Kerosene is a light colorless liquid.

Soluble- the term characterizes solid or gaseous substance, which can be dissolved in liquid; this liquid is usually water. A substance can be characterized as readily soluble, sparingly soluble, sparingly soluble, insoluble or soluble. For example, sugar is soluble in water (sugar can be dissolved in water), lime is slightly soluble in water, solubility.

Insoluble- the term characterizes a solid or gaseous substance that does not dissolve in a liquid. This concept is opposite in meaning to the term soluble . Very few substances are completely insoluble.

Slightly soluble- the term characterizes a substance, only a small part of which is soluble in liquid. For example, lime is slightly soluble in water.

Poorly soluble- the term characterizes a substance, only a very small part of which is soluble in liquid, much less than that of a slightly soluble substance. For example, air is poorly soluble in water.

Flaky- the term characterizes a sediment that looks like wool fibers floating in a liquid. For example, the precipitate of aluminum hydroxide is flaky.

Lactic- the term characterizes a liquid with a white sediment that gives the liquid the appearance of milk. This sediment is very light. For example, passing carbon dioxide through lime water produces a light precipitate of calcium carbonate, which turns the lime water into a milky liquid.

Defending- the term characterizes a white (“creamy”) sediment that is heavier than the sediment that forms the milky liquid, but still floats in the liquid and slowly settles in it. For example, silver chloride forms a settling precipitate.

Heavy- the term characterizes the sediment that sinks to the bottom of a vessel with liquid. For example, barium sulfate forms a heavy precipitate.

Mixable- the term characterizes liquids that can be mixed in all proportions; As a result, a homogeneous liquid is formed. For example, water and alcohol can completely mix with each other and appear as a homogeneous liquid as a result.

Immiscible- the term characterizes liquids that do not mix with each other at all. For example, oil and water form two layers of liquid because oil and water are immiscible liquids.

Layer- a flat portion of a substance lying on the surface of another substance or between two substances. The layer can be thick or thin. For example, a layer of peel covers an orange, a sandwich has three layers - bread, sausage and more bread.

Film- a thin layer of substance. It can be a thin layer of liquid, vapor or solid, a thin layer of one liquid on another liquid, a thin layer of a solid on another solid. For example, a thin film of oil on water, a thin film of oxide on metal.

Interface boundary (surface)- the point of contact between two layers of liquid, a solid and a liquid, or two solids. For example, if oil floats on water, then the place where they touch is the interface.

Viscosity- a property of a liquid that prevents it fast current. For example, olive oil has a high viscosity, water has a very low viscosity.

Volatile- the term characterizes a liquid that evaporates easily. For example, gasoline is a highly volatile liquid.

The world around us is material. There are two types of matter: substance and field. The object of chemistry is a substance (including the influence of various fields on the substance - sound, magnetic, electromagnetic, etc.)

Matter is everything that has rest mass (i.e. is characterized by the presence of mass when it is not moving). So, although the rest mass of one electron (the mass of a non-moving electron) is very small - about 10 -27 g, but even one electron is matter.

Substance exists in three states of aggregation - gaseous, liquid and solid. There is another state of matter - plasma (for example, there is plasma in thunderstorms and ball lightning), but in school course Plasma chemistry is almost not considered.

Substances can be pure, very pure (needed, for example, to create fiber optics), they can contain noticeable amounts of impurities, or they can be mixtures.

All substances are made up of tiny particles called atoms. Substances consisting of atoms of the same type(from atoms of one element), called simple(for example, charcoal, oxygen, nitrogen, silver, etc.). Substances that contain atoms of different elements interconnected are called complex.

If a substance (for example, air) contains two or larger number simple substances, and their atoms are not connected to each other, then it is not called a complex substance, but a mixture of simple substances. The number of simple substances is relatively small (about five hundred), but the number of complex substances is huge. To date, tens of millions of different complex substances are known.

Chemical transformations

Substances are able to interact with each other, and new substances arise. Such transformations are called chemical. For example, a simple substance coal interacts (chemists say it reacts) with another simple substance - oxygen, resulting in the formation compound– carbon dioxide, in which carbon and oxygen atoms are connected to each other. Such transformations of one substance into another are called chemical. Chemical transformations are chemical reactions. So, when sugar is heated in air, a complex sweet substance - sucrose (which sugar is made of) - turns into a simple substance - coal and a complex substance - water.

Chemistry studies the transformation of one substance into another. The task of chemistry is to find out with which substances a particular substance can interact (react) under given conditions and what is formed. In addition, it is important to find out under what conditions a particular transformation can occur and the desired substance can be obtained.

Physical properties substances

Each substance is characterized by a set of physical and chemical properties. Physical properties are properties that can be characterized using physical instruments. For example, using a thermometer you can determine the melting and boiling points of water. Physical methods can be used to characterize the ability of a substance to conduct electricity, determine the density of a substance, its hardness, etc. At physical processes substances remain unchanged in composition.

The physical properties of substances are divided into countable (those that can be characterized using certain physical instruments by number, for example, by indicating density, melting and boiling points, solubility in water, etc.) and innumerable (those that cannot be characterized by number or is very difficult - such as color, smell, taste, etc.).

Chemical properties of substances

The chemical properties of a substance are a set of information about what other substances and under what conditions a given substance enters into chemical interactions. The most important task of chemistry is to identify the chemical properties of substances.

Participates in chemical transformations tiny particles substances - atoms. During chemical transformations, other substances are formed from some substances, and the original substances disappear, and new substances (reaction products) are formed in their place. A atoms at everyone chemical transformations are preserved. Their rearrangement occurs; during chemical transformations, old bonds between atoms are destroyed and new bonds arise.

Chemical element

Number various substances huge (and each of them has its own set of physical and chemical properties). There are relatively few atoms in the material world around us that differ from each other in their most important characteristics - about a hundred. Each type of atom has its own chemical element. A chemical element is a collection of atoms with the same or similar characteristics. About 90 different chemical elements are found in nature. To date, physicists have learned to create new types of atoms that are not found on Earth. Such atoms (and, accordingly, such chemical elements) are called artificial (in English - man-made elements). More than two dozen artificially obtained elements have been synthesized to date.

Each element has a Latin name and a one- or two-letter symbol. In Russian-language chemical literature there are no clear rules for pronunciation of symbols of chemical elements. Some pronounce it like this: they call the element in Russian (symbols for sodium, magnesium, etc.), others - according to Latin letters(symbols of carbon, phosphorus, sulfur), the third - what the name of the element sounds like in Latin (iron, silver, gold, mercury). We usually pronounce the symbol of the element hydrogen H the way this letter is pronounced in French.

Comparison the most important characteristics chemical elements and simple substances are given in the table below. One element may correspond to several simple substances (the phenomenon of allotropy: carbon, oxygen, etc.), or perhaps just one (argon and other inert gases).

State	Properties
Gaseous	1. The ability to take on the volume and shape of a vessel. 2. Compressibility. 3. Fast diffusion (chaotic movement of molecules). 4. E kinetic. > E potential
	1. The ability to take the shape of that part of the vessel that the substance occupies. 2. Failure to expand to fill the vessel. 3. Low compressibility. 4. Slow diffusion. 5. Fluidity. 6. E kinetic. = E potential
	1. The ability to maintain the characteristic shape and volume. 2. Low compressibility (under pressure). 3. Very slow diffusion due to oscillatory movements particles. 4. No turnover. 5. E kinetic.< Е потенц.

The state of aggregation of a substance is determined by the forces acting between molecules, the distance between particles and the nature of their movement.

IN hard state, the particles occupy a certain position relative to each other. It has low compressibility and mechanical strength, since the molecules do not have freedom of movement, but only vibration. The molecules, atoms, or ions that form a solid are called structural units. Solids are divided into amorphous and crystalline(Table 27 ).

Table 33

Comparative characteristics of amorphous and crystalline substances

Substance	Characteristic
Amorphous	1. Short-range order of particle arrangement. 2. Isotropy of physical properties. 3. No specific melting point. 4. Thermodynamic instability (large reserve of internal energy). 5. Fluidity. Examples: amber, glass, organic polymers, etc.
Crystalline	1. Long-range order of particle arrangement. 2. Anisotropy of physical properties. 3. Specific melting point. 4. Thermodynamic stability (low internal energy reserve). 5. There are elements of symmetry. Examples: metals, alloys, solid salts, carbon (diamond, graphite), etc.

Crystalline substances melt at a strictly defined temperature (Tm), amorphous substances do not have a clearly defined melting point; when heated, they soften (characterized by a softening interval) and pass into a liquid or viscous state. The internal structure of amorphous substances is characterized by a random arrangement of molecules . The crystalline state of a substance presupposes the correct arrangement in space of the particles that make up the crystal, and the formation crystalline (spatial)grates. The main feature of crystalline bodies is their anisotropy - dissimilarity of properties (thermal and electrical conductivity, mechanical strength, dissolution rate, etc.) according to different directions, while amorphous bodies isotropic .

Solidcrystals- three-dimensional formations characterized by strict repeatability of the same structural element (unit cell) in all directions. Unit cell- represents the smallest volume of a crystal in the form of a parallelepiped, repeated in the crystal an infinite number of times.

Main settings crystal lattice :

Energy of the crystal lattice (E cr. , kJ/mol) – This is the energy that is released during the formation of 1 mole of a crystal from microparticles (atoms, molecules, ions) that are in a gaseous state and separated from each other at a distance that precludes their interaction.

Lattice constant ( d , [ A 0 ]) – the smallest distance between the center of two particles in a crystal connected by a chemical bond.

Coordination number (c.n.) – the number of particles surrounding the central particle in space, connected to it by a chemical bond.

The points at which crystal particles are located are called crystal lattice nodes

Despite the variety of crystal shapes, they can be classified. Systematization of crystal forms was introduced A.V. Gadolin(1867), it is based on the features of their symmetry. In accordance with the geometric shape of crystals, the following systems (systems) are possible: cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal and rhombohedral (Fig. 18).

The same substance can have different crystalline forms, which differ in internal structure, and therefore in terms of physicochemical properties. This phenomenon is called polymorphism . Isomorphism – two substances of different nature form crystals of the same structure. Such substances can replace each other in the crystal lattice, forming mixed crystals.

Rice. 18. Basic crystal systems.

Depending on the type of particles located at the nodes of the crystal lattice and the type of bonds between them, crystals are of four types: ionic, atomic, molecular and metallic(rice . 19).

Rice. 19. Types of crystals

Characteristics of crystal lattices are presented in table. 34.

Properties of matter	Oxygen	Acetic acid	Aluminum
1. Physical state under normal conditions	Gas	Liquid	Solid
2. Color	No color	No color	Silver white
3. Taste	Tasteless	Sour	Tasteless
4. Smell	Doesn't have	Sharp specific	Doesn't have
5. Water solubility	Poorly soluble	Soluble	Practically insoluble
6. Thermal conductivity	Low	Small	High
7. Electrical conductivity	Absent	Small	High

Knowledge of the properties of substances is necessary for their practical application. For example, Figure 6 shows the applications of aluminum due to the properties of this metal.

1. What academic subjects Are they considered natural?

2. Give examples of positive human impact on the environment.

3. Give examples of the negative impact of humans on nature.

4. What does chemistry study?

5. From the following list of names, write down bodies and substances separately: snowflake, dew drop, water, piece of ice, granulated sugar, sugar cube, chalk, school chalk. How many bodies and how many substances are named in this list?

6. Compare the properties of substances (that is, establish the common and different between them):

A) carbon dioxide and oxygen;

b) nitrogen and carbon dioxide;

c) sugar and salt;

d) acetic and citric acids.

7. What properties of aluminum underlie its use?

8. Why do they begin to study chemistry later than biology, geography, and physics?

Man is connected with the world around him by thousands of invisible threads, and he himself is a part of it. Nature provides everything necessary for human life, provides for his daily needs, and gives unspeakable pleasure from communicating with her.

However, the relationship between man and the environment is very difficult. On the one hand, a person admires nature and glorifies it in poetry, reflects nature in excellent paintings and photographs (Fig. 1).

Rice. 1.
“How beautiful this world is, look!”

On the other hand, growth environmental problems- sad retribution for numerous human mistakes and mistakes: deforestation, extermination of animals, pollution environment industrial and household waste etc. (Fig. 2).

Rice. 2.
And this is what it looks like beautiful world as a result of human activity:
a - deforestation; b - atmospheric poisoning by industrial emissions; c - pollution of water bodies; d - forest clearing turned into a landfill

In order for the relationship between man and nature to be kind and harmonious, it is necessary to know and understand it, treat it with care, use it wisely and rationally natural resources. Natural science subjects are designed to teach understanding the world around us, knowledge of the laws of its existence: biology, geography, chemistry, physics (Fig. 3). You have already met some of them at previous stages of school.

Rice. 3.
Biology, geography, physics, chemistry belong to the natural sciences

This year you are starting to study physics. And only a year later, in the 8th grade, you will get acquainted with another academic subject - chemistry.

Chemistry is the science of substances, their structure, properties and transformations of some substances into others.

All the objects around us are usually called physical bodies, and what they consist of is called substances (Fig. 4).

Rice. 4.
Physical bodies and corresponding chemical substances:
a - steel products and iron powder; b - computer components and various plastics; V - solar battery and silicon

Every body has shape and volume. In turn, each substance is individual and unique in its characteristics - properties: state of aggregation, density, color, shine, smell, taste, hardness, plasticity, solubility in water, ability to conduct heat and electric current.

Let us describe, for example, the properties of three substances in different states of aggregation under normal conditions: oxygen, acetic acid and aluminum (Table 1).

Table 1
Properties of oxygen, acetic acid and aluminum

Knowledge of the properties of substances is necessary for their practical use. For example, Figure 5 shows the applications of aluminum due to the properties of this metal.

Rice. 5.
Applications of aluminum based on its properties

Many substances are toxic, explosive, flammable, and therefore require careful and competent handling when working with them.

Our book is designed to prepare you for the study of this serious and important subject and is therefore called “Chemistry. Introductory course."

Whether chemistry is a completely new discipline for you, you will find out in the following paragraphs.

1. Chemistry is part of natural science.
2. Relationships between man and the environment.
3. Physical bodies and substances.
4. Properties of substances.
5. Application of substances based on their properties.

Questions and tasks

1. What subjects are considered natural?
2. Give examples of positive human impact on the environment.
3. Give examples of the negative impact of humans on nature.
4. What does chemistry study?
5. From the following list of names, write down bodies and substances separately: snowflake, dew drop, water, piece of ice, granulated sugar, sugar cube, chalk, school chalk. How many bodies and how many substances are named in this list?
6. Compare the properties of substances (i.e., establish similarities and differences between them):

   a) carbon dioxide and oxygen;
   b) nitrogen and carbon dioxide;
   c) sugar and salt;
   d) acetic and citric acid.

7. What properties of aluminum underlie its use (see Fig. 5)?