The main difference between them is their composition. Thus, simple substances include atoms of one element. Their (simple substances) crystals can be synthesized in the laboratory, and sometimes at home. However, it is often necessary to create certain conditions for storing the resulting crystals.

There are five classes into which simple substances are divided: metals, semimetals, nonmetals, intermetallic compounds, and halogens (not found in nature). They can be represented by atomic (Ar, He) or molecular (O2, H2, O3) gases.

As an example, we can take the simple substance oxygen. It includes molecules consisting of two atoms of the element Oxygen. Or, for example, the substance iron consists of crystals containing only atoms of the element Iron. Historically, it was customary to name a simple substance by the name of the element whose atoms are included in its composition. The structure of these compounds can be molecular or non-molecular.

Complex substances include atoms various types and upon decomposition can form two (or more) compounds. For example, when water splits, it forms oxygen and hydrogen. However, not every compound can be broken down into simple substances. For example, iron sulfide, formed by sulfur and iron atoms, cannot be broken down. In this case, in order to prove that the compound is complex and includes dissimilar atoms, the reverse reaction principle is used. In other words, iron sulfide is obtained using the starting components.

Simple substances are forms of chemical elements that exist in free form. Today science knows more than four hundred types of these elements.

Unlike complex substances, simple substances cannot be obtained from other simple substances. They also cannot be decomposed into other compounds.

All allotropic modifications have the property of transforming into each other. Different types simple substances formed by one chemical element can have different and different levels chemical activity. For example, oxygen exhibits less activity than ozone, and the melting point of fullerene, for example, is lower than that of diamond.

IN normal conditions for eleven elements, simple substances will be gases (Ar, Xe, Rn, N, H, Ne, O, F, Kr, Cl, He,), for two liquids (Br, Hg), and for other elements - solids.

At temperatures close to room temperature, the five metals will take on a liquid or semi-liquid state. This is due to the fact that their melting point is almost equal. Thus, mercury and rubidium melt at 39 degrees, francium at 27, cesium at 28, and gallium at 30 degrees.

It should be noted that the concepts of “chemical element”, “atom”, “simple substance” should not be confused. So, for example, an atom has a certain specific meaning and it really exists. The definition of “chemical element” is generally abstract and collective. In nature, elements are present in the form of free or chemically bonded atoms. At the same time, the characteristics of simple substances (collections of particles) and chemical elements (isolated atoms) specific type) have their own characteristics.

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.

The substance comes 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), may contain noticeable amounts of impurities, may 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 bonded to each other different elements, are called complex.

If a substance (for example, air) contains two or more 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 enormous. 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 of a complex substance - carbon dioxide, in which the 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. By physical methods can 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 it enters into contact. chemical interactions this substance. The most important task chemistry - identifying the chemical properties of substances.

IN chemical transformations The smallest particles of substances involved are atoms. During chemical transformations, other substances are formed from some substances, and starting materials disappear, and instead of them new substances (reaction products) are formed. 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). Atoms that differ from each other in their most important characteristics in the environment around us material world relatively small - 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 Latin name and a one- or two-letter character. 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).

Under chemical element understand a collection of atoms with the same positive nuclear charge and with a certain set of properties. Atoms of the same chemical element combine to form simple substance. When atoms of different chemical elements combine, complex substances (chemical compounds) or mixtures. Difference chemical compounds from mixtures is that:

They have new properties that the simple substances from which they were obtained did not have;

They cannot be mechanically divided into their component parts;

Chemical elements in their composition can only be in strictly defined quantitative ratios.

Some chemical elements (carbon, oxygen, phosphorus, sulfur) can exist in the form of several simple substances. This phenomenon is called allotropy, and varieties of simple substances of the same chemical element are called its allotropic modifications(modifications).

Tasks

1.1. What more exists in nature: chemical elements or simple substances? Why?

1.2. Is it true that sulfur and iron are included in the composition of iron sulfide as substances? If not, what is the correct answer?

1.3. Name allotropic modifications of oxygen. Do they differ in their properties? If so, how?

1.4. Which of the allotropic modifications of oxygen is chemically more active and why?

1.5. The simple substances or chemical elements are zinc, sulfur and oxygen in the following reactions:

1) CuSO 4 + Zn = ZnSO 4 + Cu;

2) S + O 2 = SO 2;

3) Zn + 2HC1 = ZnCl 2 + H 2 ;

4) Zn + S = ZnS;

5) 2H 2 0 = 2H 2  + O 2 .

1.6. Is it possible to get another simple substance from one simple substance? Give a reasoned answer.

1.7. When a substance is burned in oxygen, sulfur (IV) oxide, nitrogen and water are produced. What chemical elements form the starting substance?

1.8. Indicate whether simple or complex substances include: H 2 O, C1 2, NaOH, O 2, HNO 3, Fe, S, ZnSO 4, N 2, AgCl, I 2, A1 2 O 3, O 3?

1.9. For which chemical elements are allotropic modifications known? Name these modifications.

1.10. Is it possible for a chemical element to transition from one allotropic modification to another? Give examples.

1.11. What chemical elements do they mean when they talk about diamond and ozone?

1.12. Which of the substances are chemical compounds and which are mixtures:

2) air;

4) sulfuric acid;

1.13. How to prove that sodium chloride is a complex substance?

1.14. Name three allotropic modifications of carbon.

1.15. What are allotropic modifications of phosphorus called and how do they differ from each other?

1.16. What are allotropic modifications of sulfur called and how do they differ from each other?

1.17. Indicate which of the statements is true and why - the composition of barium sulfate includes:

1) simple substances barium, sulfur, oxygen;

2) chemical elements barium, sulfur, oxygen.

1.18. How many liters of ammonia can be produced from a mixture of 10 liters of nitrogen and 30 liters of hydrogen?

1.19. How many liters of water vapor are produced from a mixture of 10 liters of hydrogen and 4 liters of oxygen? What gas and in what volume will remain in excess?

1.20. How many grams of zinc sulfide (ZnS) can be formed from a mixture of 130 g of zinc and 48 g of sulfur?

1.22. What is a solution of alcohol in water - a mixture or a chemical compound?

1.23. Can a complex substance consist of atoms of the same type?

1.24. Which of the following substances are mixtures and which are chemical compounds:

1) bronze;

2) nichrome;

3) kerosene;

4) potassium nitrate:

5) rosin;

6) superphosphate.

1.25. Given a mixture of Cl 2 + HCl + CaCl 2 + H 2 O.

1) How many different substances are in the mixture;

2) How many chlorine molecules are in the mixture;

3) How many chlorine atoms are in the mixture;

4) How many molecules of different substances are contained in the mixture.

All substances are divided into simple and complex.

Simple substances- These are substances that consist of atoms of one element.

In some simple substances, atoms of the same element combine with each other to form molecules. Such simple substances have molecular structure . These include: , . All these substances consist of diatomic molecules. (Note that the names of the simple substances are the same as the names of the elements!)

Other simple substances have atomic structure , i.e. they consist of atoms between which there are certain bonds. Examples of such simple substances are all (, etc.) and some (, etc.). Not only the names, but also the formulas of these simple substances coincide with the symbols of the elements.

There is also a group of simple substances called. These include: helium He, neon Ne, argon Ar, krypton Kr, xenon Xe, radon Rn. These simple substances are made up of atoms that are not bonded to each other.

Each element forms at least one simple substance. Some elements can form not one, but two or more simple substances. This phenomenon is called allotropy.

Allotropy is the phenomenon of the formation of several simple substances by one element.

Different simple substances that are formed by the same chemical element are called allotropic modifications(modifications).

Allotropic modifications may differ from each other in molecular composition. For example, the element oxygen forms two simple substances. One of them consists of diatomic molecules O 2 and has the same name as the element-. Another simple substance consists of triatomic O 3 molecules and has proper name- ozone.

Oxygen O 2 and ozone O 3 have different physical and Chemical properties.

Allotropic modifications can be solids that have different crystal structures. An example is the allotropic modifications of carbon C - diamond and graphite.

The number of known simple substances (approximately 400) is significantly greater than the number of chemical elements, since many elements can form two or more allotropic modifications.

Complex substances- These are substances that consist of atoms of different elements.

Examples of complex substances: HCl, H 2 O, NaCl, CO 2, H 2 SO 4, etc.

Complex substances are often called chemical compounds. In chemical compounds, the properties of the simple substances from which these compounds are formed are not preserved. The properties of a complex substance differ from the properties of the simple substances from which it is formed.

For example, chloride sodium NaCl can be formed from simple substances - sodium metal Na and chlorine gas Cl The physical and chemical properties of NaCl differ from the properties of Na and Cl 2.

In nature, as a rule, they are not found pure substances, but mixtures of substances. IN practical activities we also usually use mixtures of substances. Any mixture consists of two or more substances called mixture components.

For example, air is a mixture of several gaseous substances: oxygen O 2 (21% by volume), (78%), etc. Mixtures are solutions of many substances, alloys of some metals, etc.

Mixtures of substances are homogeneous (homogeneous) and heterogeneous (heterogeneous).

Homogeneous mixtures- These are mixtures in which there is no interface between the components.

Mixtures of gases (in particular, air) and liquid solutions (for example, a solution of sugar in water) are homogeneous.

Heterogeneous mixtures- These are mixtures in which the components are separated by an interface.

Heterogeneous include mixtures of solids (sand + chalk powder), mixtures of liquids insoluble in each other (water + oil), mixtures of liquids and solids insoluble in it (water + chalk).

Key differences mixtures of chemical compounds:

1. In mixtures, the properties of individual substances (components) are preserved.
2. The composition of mixtures is not constant.

About atoms and chemical elements

There is nothing else in nature

neither here nor there, in the depths of space:

everything - from small grains of sand to planets -

consists of unified elements.

S. P. Shchipachev, “Reading Mendeleev.”

In chemistry, except for terms "atom" And "molecule" the concept is often used "element". What do these concepts have in common and how do they differ?

Chemical element – these are atoms of the same type . So, for example, all hydrogen atoms are the element hydrogen; all oxygen and mercury atoms are the elements oxygen and mercury, respectively.

Currently, more than 107 types of atoms are known, that is, more than 107 chemical elements. It is necessary to distinguish between the concepts of “chemical element”, “atom” and “simple substance”

Simple and complex substances

According to their elemental composition they are distinguished simple substances, consisting of atoms of one element (H 2, O 2, Cl 2, P 4, Na, Cu, Au), and complex substances, consisting of atoms of different elements (H 2 O, NH 3, OF 2, H 2 SO 4, MgCl 2, K 2 SO 4).

Currently, 115 chemical elements are known, which form about 500 simple substances.

Native gold is a simple substance.

The ability of one element to exist in the form of various simple substances differing in properties is called allotropy For example, the element oxygen O has two allotropic forms - dioxygen O 2 and ozone O 3 with different numbers of atoms in the molecules.

Allotropic forms of the element carbon C - diamond and graphite - differ in the structure of their crystals. There are other reasons for allotropy.

chemical compounds, for example, mercury(II) oxide HgO (obtained by combining atoms of simple substances - mercury Hg and oxygen O 2), sodium bromide (obtained by combining atoms of simple substances - sodium Na and bromine Br 2).

So, let's summarize the above. There are two types of molecules of matter:

1. Simple– the molecules of such substances consist of atoms of the same type. In chemical reactions they cannot decompose to form several simpler substances.

2. Complex- molecules of such substances consist of atoms different types. In chemical reactions they can decompose to form simpler substances.

The difference between the concepts of “chemical element” and “simple substance”

Distinguish between concepts "chemical element" And “simple substance” possible by comparing the properties of simple and complex substances. For example, a simple substance - oxygen– a colorless gas necessary for breathing and supporting combustion. smallest particle The simple substance oxygen is a molecule that consists of two atoms. Oxygen is also included in carbon monoxide ( carbon monoxide) and water. However, water and carbon monoxide contain chemically bound oxygen, which does not have the properties of a simple substance; in particular, it cannot be used for respiration. Fish, for example, do not breathe chemically bound oxygen, which is part of the water molecule, but free oxygen dissolved in it. That's why when we're talking about about the composition of any chemical compounds, it should be understood that these compounds do not include simple substances, but atoms certain type, that is, the corresponding elements.

When complex substances decompose, atoms can be released in a free state and combine to form simple substances. Simple substances consist of atoms of one element. The difference between the concepts of “chemical element” and “simple substance” is also confirmed by the fact that the same element can form several simple substances. For example, atoms of the element oxygen can form diatomic molecules oxygen and triatomic - ozone. Oxygen and ozone are completely different simple substances. This explains the fact that much more simple substances are known than chemical elements.

Using the concept of “chemical element”, we can give the following definition to simple and complex substances:

Simple substances are those that consist of atoms of one chemical element.

Complex substances are those that consist of atoms of different chemical elements.

The difference between the concepts of “mixture” and “chemical compound”

Complex substances are often called chemical compounds.

Try to answer the questions:

1. How do mixtures differ in composition from chemical compounds?

2. Compare the properties of mixtures and chemical compounds?

3. In what ways can you separate the components of a mixture and a chemical compound?

4. Is it possible to judge by external signs about the formation of a mixture and a chemical compound?

Comparative characteristics of mixtures and chemicals

Tasks for consolidation

I. Work with simulators

II. Solve the problem

№1

How many simple substances are written in a series of formulas:
H 2 O, N 2, O 3, HNO 3, P 2 O 5, S, Fe, CO 2, KOH.

№2

Both substances are complex:

A) C (coal) and S (sulfur);
B) CO 2 (carbon dioxide) and H 2 O (water);
B) Fe (iron) and CH 4 (methane);
D) H 2 SO 4 (sulfuric acid) and H 2 (hydrogen).

№3

Choose the correct statement:
Simple substances consist of atoms of the same type.

A) Correct

B) Incorrect

№4

What is typical for mixtures is that
A) They have a constant composition;
B) Substances in the “mixture” do not retain their individual properties;
C) Substances in “mixtures” can be separated by physical properties;
D) Substances in “mixtures” can be separated using a chemical reaction.

№5

The following are typical for “chemical compounds”:
A) Variable composition;
B) Substances contained in a “chemical compound” can be separated by physical means;
C) The formation of a chemical compound can be judged by the signs of chemical reactions;
D) Permanent composition.

№6

In what case are we talking about gland how about chemical element?
A) Iron is a metal that is attracted by a magnet;
B) Iron is part of rust;
C) Iron is characterized by a metallic luster;
D) Iron sulfide contains one iron atom.

№7

In what case are we talking about oxygen as a simple substance?
A) Oxygen is a gas that supports respiration and combustion;
B) Fish breathe oxygen dissolved in water;
C) The oxygen atom is part of the water molecule;
D) Oxygen is part of air.