In the previous chapter, it was said that not only atoms of one chemical element, but also atoms of different elements can form bonds with each other. Substances formed by atoms of one chemical element are called simple substances, and substances formed by atoms of different chemical elements are complex. Some simple substances have a molecular structure, i.e. are made up of molecules. For example, substances such as oxygen, nitrogen, hydrogen, fluorine, chlorine, bromine, and iodine have a molecular structure. Each of these substances is formed by diatomic molecules, so their formulas can be written as O 2, N 2, H 2, F 2, Cl 2, Br 2 and I 2, respectively. As you can see, simple substances can have the same name with the elements that form them. Therefore, one should clearly distinguish between situations when it comes to a chemical element, and when it is about a simple substance.

Often, simple substances have not a molecular, but an atomic structure. In such substances, atoms can form various types of bonds with each other, which will be discussed in detail a little later. Substances of this structure are all metals, for example, iron, copper, nickel, as well as some non-metals - diamond, silicon, graphite, etc. For these substances, not only the name of the chemical element coincides with the name of the substance formed by it, but the formula of the substance and the designation of the chemical element are also identical. For example, the chemical elements iron, copper and silicon, which have the designations Fe, Cu and Si, form simple substances, the formulas of which are Fe, Cu and Si, respectively. There is also a small group of simple substances, consisting of disparate atoms, not connected in any way. Such substances are gases, which are called, due to their extremely low chemical activity, noble. These include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn).

Since there are only about 500 known simple substances, it follows logically that many chemical elements are characterized by a phenomenon called allotropy.

Allotropy is the phenomenon when one chemical element can form several simple substances. Different chemicals formed by one chemical element are called allotropic modifications or allotropes.

So, for example, the chemical element oxygen can form two simple substances, one of which has the name of the chemical element - oxygen. Oxygen as a substance consists of diatomic molecules, i.e. its formula is O 2 . It is this compound that is part of the vital air we need. Another allotropic modification of oxygen is the triatomic gas ozone, whose formula is O 3 . Despite the fact that both ozone and oxygen are formed by the same chemical element, their chemical behavior is very different: ozone is much more active than oxygen in reactions with the same substances. In addition, these substances differ from each other in physical properties already at least due to the fact that the molecular weight of ozone is 1.5 times greater than that of oxygen. This leads to the fact that its density in the gaseous state is also 1.5 times greater.

Many chemical elements tend to form allotropic modifications that differ from each other in the structural features of the crystal lattice. So, for example, in Figure 5, you can see schematic representations of fragments of the crystal lattices of diamond and graphite, which are allotropic modifications of carbon.

Figure 5. Fragments of crystal lattices of diamond (a) and graphite (b)

In addition, carbon can also have a molecular structure: such a structure is observed in such a type of substances as fullerenes. Substances of this type are formed by spherical carbon molecules. Figure 6 shows 3D models of the c60 fullerene molecule and a soccer ball for comparison. Note their interesting resemblance.

Figure 6. C60 fullerene molecule (a) and soccer ball (b)

Compounds are substances that are made up of atoms of different elements. They, like simple substances, can have a molecular and non-molecular structure. The non-molecular type of structure of complex substances can be more diverse than that of simple ones. Any complex chemical substances can be obtained either by direct interaction of simple substances, or by a sequence of their interactions with each other. It is important to be aware of one fact, which is that the properties of complex substances, both physical and chemical, are very different from the properties of the simple substances from which they are derived. For example, salt, which has the NaCl forum and is a colorless transparent crystal, can be obtained by reacting sodium, which is a metal with properties characteristic of metals (luster and electrical conductivity), with chlorine Cl 2, a yellow-green gas.

Sulfuric acid H 2 SO 4 can be formed by a series of successive transformations from simple substances - hydrogen H 2 , sulfur S and oxygen O 2 . Hydrogen is a gas lighter than air that forms explosive mixtures with air, sulfur is a yellow solid that can burn, and oxygen is a gas slightly heavier than air in which many substances can burn. Sulfuric acid, which can be obtained from these simple substances, is a heavy oily liquid with strong water-removing properties, due to which it chars many substances of organic origin.

Obviously, in addition to individual chemicals, there are also mixtures of them. It is mainly mixtures of various substances that form the world around us: metal alloys, food, drinks, various materials that make up the objects around us.

For example, the air we breathe consists mainly of nitrogen N 2 (78%), oxygen that is vital for us (21%), while the remaining 1% is impurities of other gases (carbon dioxide, noble gases, etc.).

Mixtures of substances are divided into homogeneous and heterogeneous. Homogeneous mixtures are those mixtures that do not have phase boundaries. Homogeneous mixtures are a mixture of alcohol and water, metal alloys, a solution of salt and sugar in water, mixtures of gases, etc. Heterogeneous mixtures are those mixtures that have a phase boundary. Mixtures of this type include a mixture of sand and water, sugar and salt, a mixture of oil and water, etc.

The substances that make up mixtures are called components.

Mixtures of simple substances, unlike chemical compounds that can be obtained from these simple substances, retain the properties of each component.

All substances that we talk about in the school chemistry course are usually divided into simple and complex. Simple substances are those substances whose molecules contain atoms of the same element. Atomic oxygen (O), molecular oxygen (O2) or simply oxygen, ozone (O3), graphite, diamond are examples of simple substances that form the chemical elements oxygen and carbon. Compounds are divided into organic and inorganic. Among inorganic substances, the following four classes are primarily distinguished: oxides (or oxides), acids (oxygenous and oxygen-free), bases (water-soluble bases are called alkalis) and salts. Compounds of non-metals (excluding oxygen and hydrogen) are not included in these four classes, we will call them conditionally "and other complex substances."

Simple substances are usually divided into metals, non-metals and inert gases. Metals include all chemical elements whose d- and f-sublevels are being filled, these are elements in the 4th period: Sc - Zn, in the 5th period: Y - Cd, in the 6th period: La - Hg, Ce - Lu, in the 7th period Ac - Th - Lr. If we now draw a line from Be to At among the remaining elements, then metals will be located to the left and below it, and non-metals to the right and top. Group 8 of the Periodic Table contains inert gases. Elements located on the diagonal: Al, Ge, Sb, Po (and some others. For example, Zn) in the free state have the properties of metals, and hydroxides have the properties of both bases and acids, i.e. are amphoteric hydroxides. Therefore, these elements can be considered metal-non-metals, occupying an intermediate position between metals and non-metals. Thus, the classification of chemical elements depends on what properties their hydroxides will have: basic - it means metal, acidic - non-metal, and both (depending on conditions) - metal-non-metal. The same chemical element in compounds with the lowest positive oxidation state (Mn + 2, Cr + 2) exhibits pronounced "metallic" properties, and in compounds with the maximum positive oxidation state (Mn + 7, Cr + 6) it exhibits the properties of a typical non-metal. To see the relationship of simple substances, oxides, hydroxides and salts, we present a summary table.

The environment is material. Matter is of two types: substance and field. The object of chemistry is a substance (including the influence on the substance of various fields - sound, magnetic, electromagnetic, etc.)

Substance - everything that has a rest mass (i.e., it 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 a substance.

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

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

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

If a substance (for example, in air) contains two or more simple substances, and their atoms are not interconnected, then it is called not a complex, but a mixture of simple substances. The number of simple substances is relatively small (about five hundred), while 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 - reacts) with another simple substance - oxygen, resulting in the formation of a complex substance - carbon dioxide, in which carbon and oxygen atoms are bonded. 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 consists of) - turns into a simple substance - coal and a complex substance - water.

Chemistry is the study of the transformation of one substance into another. The task of chemistry is to find out with which substances this or that substance can interact (react) under given conditions, what is formed in this case. In addition, it is important to find out under what conditions this or that transformation can proceed and the desired substance can be obtained.

Physical properties of substances

Each substance is characterized by a combination 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 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 devices by a number, for example, indicating density, melting and boiling points, solubility in water, etc.) and innumerable (those that cannot be characterized by a number or 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.

Chemical transformations involve the smallest particles of substances - atoms. During chemical transformations, other substances are formed from some substances, and the original substances disappear, and instead of them new substances (reaction products) are formed. A atoms at all chemical transformations are preserved. Their rearrangement occurs, during chemical transformations, old bonds between atoms are destroyed and new bonds arise.

Chemical element

The number of different substances is 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, differing 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.. There are about 90 different chemical elements found in nature. To date, physicists have learned how to create new types of atoms that are absent 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. There are no clear rules for the pronunciation of the symbols of chemical elements in the Russian-language chemical literature. Some pronounce it like this: they call the element in Russian (symbols of sodium, magnesium, etc.), others - in Latin letters(symbols of carbon, phosphorus, sulfur), the third - how the name of the element sounds in Latin (iron, silver, gold, mercury). It is customary to pronounce the symbol of the hydrogen element H in the same way as this letter is pronounced in French.

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

When studying the material of the previous paragraphs, you have already become acquainted with some substances. So, for example, a hydrogen gas molecule consists of two atoms of the chemical element hydrogen - H + H = H2.

Simple substances are substances that contain atoms of the same type.

Simple substances, from among the substances known to you, include: oxygen, graphite, sulfur, nitrogen, all metals: iron, copper, aluminum, gold, etc. Sulfur is made up of only atoms of the chemical element sulfur, while graphite is made up of atoms of the chemical element carbon.

It is necessary to clearly distinguish between concepts "chemical element" And "simple substance". For example, diamond and carbon are not the same thing. Carbon is a chemical element, and diamond is a simple substance formed by the chemical element carbon. In this case, a chemical element (carbon) and a simple substance (diamond) are called differently. Often a chemical element and a simple substance corresponding to it are called the same. For example, the element oxygen corresponds to a simple substance - oxygen.

Distinguish where in question about the element, and where about the substance, you need to learn! For example, when they say that oxygen is part of water, we are talking about the element oxygen. When they say that oxygen is a gas necessary for breathing, we are talking about a simple substance, oxygen.

Simple substances of chemical elements are divided into two groups - metals and non-metals.

Metals and non-metals fundamentally different in their physical properties. All metals are solids under normal conditions, with the exception of mercury - the only liquid metal. Metals are opaque, have a characteristic metallic sheen. Metals are ductile and conduct heat and electricity well.

Non-metals are not similar to each other in physical properties. So, hydrogen, oxygen, nitrogen are gases, silicon, sulfur, phosphorus are solids. The only liquid non-metal, bromine, is a brown-red liquid.

If we draw a conditional line from the chemical element boron to the chemical element astatine, then in the long version Periodic System above the line are non-metallic elements, and below it - metal. In the short version of the Periodic Table, the non-metallic elements are located below this line, and both the metallic and non-metallic elements are above it. This means that it is more convenient to determine whether an element is metallic or non-metallic using the long version of the Periodic System. This division is conditional, since all elements in one way or another exhibit both metallic and non-metallic metallic properties, but in most cases this distribution is true.

Compound substances and their classification

If the composition of simple substances includes atoms of only one type, it is easy to guess that the composition of complex substances will include several types of different atoms, at least two. An example of a complex substance is water, you know its chemical formula - H2O. Water molecules are made up of two types of atoms: hydrogen and oxygen.

Complex Substances Substances that are made up of different types of atoms

Let's do the following experiment. Mix powders of sulfur and zinc. We place the mixture on a metal sheet and set it on fire with a wooden torch. The mixture ignites and quickly burns with a bright flame. After finishing chemical reaction a new substance was formed, which includes sulfur and zinc atoms. The properties of this substance are completely different from the properties starting materials- sulfur and zinc.

Complex substances are usually divided into two groups: Not organic matter and their derivatives and organic substances and their derivatives. For example, rock salt- This inorganic matter, and the starch contained in the potato is an organic substance.

Structure types of substances

According to the type of particles that make up substances, substances are divided into substances molecular and not molecular structure.

The composition of a substance can include various structural particles, such as atoms, molecules, ions. Therefore, there are three types of substances: substances of atomic, ionic and molecular structure. Substances various types buildings will have different properties.

Substances of atomic structure

An example of substances atomic structure substances may be formed by the element carbon: graphite and diamond. The composition of these substances includes only carbon atoms, but the properties of these substances are very different. Graphite- fragile, easily exfoliating substance of gray-black color. Diamond- transparent, one of the hardest mineral on the planet. Why do substances composed of the same type of atoms have different properties? It's all about the structure of these substances. Carbon atoms in graphite and diamond bond in a different way. Substances of atomic structure have high temperatures boiling and melting, generally insoluble in water, non-volatile.

Crystal lattice - an auxiliary geometric image introduced to analyze the structure of a crystal

Substances of molecular structure

Substances of molecular structure- These are almost all liquids and most gaseous substances. There are also crystalline substances, whose crystal lattice contains molecules. Water is a substance of molecular structure. Ice also has a molecular structure, but unlike liquid water, it has a crystal lattice, where all molecules are strictly ordered. Substances of a molecular structure have low boiling and melting points, are usually brittle, and do not conduct electric current.

Substances of ionic structure

Substances of ionic structure are solid crystalline substances. An example of an ionic compound substance is table salt. Its chemical formula is NaCl. As you can see, NaCl consists of ions Na+ and Cl⎺, alternating in certain places (nodes) of the crystal lattice. Substances of an ionic structure have high melting and boiling points, are brittle, as a rule, are highly soluble in water, and do not conduct electric current.

The concepts of "atom", "chemical element" and "simple substance" should not be confused.

• "Atom"- a concrete concept, since atoms really exist.
• "Chemical element" is a collective, abstract concept; in nature, a chemical element exists in the form of free or chemically bound atoms, that is, simple and complex substances.

The names of chemical elements and the corresponding simple substances coincide in most cases.

When we talk about a material or a component of a mixture - for example, a flask filled with gaseous chlorine, an aqueous solution of bromine, let's take a piece of phosphorus - we are talking about a simple substance. If we say that a chlorine atom contains 17 electrons, a substance contains phosphorus, a molecule consists of two bromine atoms, then we mean a chemical element.

It is necessary to distinguish between the properties (characteristics) of a simple substance (sets of particles) and the properties (characteristics) of a chemical element (an isolated atom of a certain type), see the table below:

Compounds must be distinguished from mixtures, which also consist of different elements.

The quantitative ratio of the components of the mixture can be variable, and the chemical compounds have a constant composition.

For example, in a glass of tea, you can add one spoonful of sugar, or several, and sucrose molecules С12Н22О11 contains exactly 12 carbon atoms, 22 hydrogen atoms and 11 oxygen atoms.

Thus, the composition of compounds can be described by one chemical formula, and the composition mixture is not.

The components of the mixture retain their physical and Chemical properties. For example, if you mix iron powder with sulfur, then a mixture of two substances is formed. Both sulfur and iron in this mixture retain their properties: iron is attracted by a magnet, and sulfur is not wetted by water and floats on its surface.

If sulfur and iron react with each other, a new compound is formed with the formula FeS, which does not have the properties of either iron or sulfur, but has a set of its own properties. In conjunction FeS iron and sulfur are bound together and cannot be separated by methods that separate mixtures.

Thus, substances can be classified according to several parameters:

Conclusions from the article on the topic Simple and complex substances

• Simple substances- substances that contain atoms of the same type
• Elements are divided into metals and non-metals
• Complex Substances Substances that are made up of different types of atoms
• Compounds are divided into organic and inorganic
• There are substances of atomic, molecular and ionic structure, their properties are different
• Crystal cell is an auxiliary geometric image introduced to analyze the crystal structure

Under chemical element understand a set of atoms with the same positive charge of the nucleus and with a certain set of properties. Atoms of the same chemical element combine to form simple substance. When atoms of different chemical elements are combined, complex substances (chemical compounds) or mixtures. The difference between chemical compounds and mixtures is that:

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

They cannot be mechanically separated 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 exists more 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 the 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. Simple substances or chemical elements are zinc, sulfur and oxygen in the following reactions:

1) СuSO 4 + Zn = ZnSO 4 + Cu;

2) S + O 2 \u003d SO 2;

3) Zn + 2HC1 = ZnCl 2 + H 2 ;

4) Zn + S = ZnS;

5) 2H 2 0 \u003d 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 certain substance is burned in oxygen, sulfur oxide (IV), nitrogen and water are obtained. What chemical elements form the original 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 allotropic modifications are known? Name these modifications.

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

1.11. What chemical elements do they mean when they talk about diamond, 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 the names of allotropic modifications of phosphorus and how do they differ from each other?

1.16. What are the 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 obtained from a mixture of 10 liters of nitrogen and 30 liters of hydrogen?

1.19. How many liters of water vapor are formed 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 be made up of atoms of the same kind?

1.24. Which of the following substances are mixtures and which 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 various substances are contained in the mixture.