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A simple substance made up of atoms. Simple and complex substances. Chemical element

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 matter. 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.

Simple and complex substances. Chemical element

About atoms and chemical elements

In chemistry, in addition to the terms “atom” and “molecule”, the concept of “element” is often used. What is common and how do these concepts differ?

Chemical element 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, that is, more than 107 chemical elements, are known. It is necessary to distinguish between the concepts of "chemical element", "atom" and "simple substance"

Simple and complex substances

By elemental composition, simple substances are distinguished, consisting of atoms of one element (H2, O2, Cl2, P4, Na, Cu, Au), and complex substances, consisting of atoms of different elements (H2O, NH3, OF2, H2SO4, MgCl2, K2SO4) .

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 that differ in properties is called allotropy. For example, the element oxygen O has two allotropic forms - dioxygen O2 and ozone O3c different number atoms in molecules.

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

Allotropic forms of carbon:

graphite:

diamond:

Complex substances are often called chemical compounds, for example, mercury (II) oxide HgO (obtained by combining atoms of simple substances - mercury Hg and oxygen O2), sodium bromide (obtained by combining atoms of simple substances - sodium Na and bromine Br2).

So let's summarize the above. Molecules of matter are of two types:

1. Simple Molecules of such substances consist of atoms of the same type. IN chemical reactions cannot decompose to form several simpler substances.

2.Complex- the molecules of such substances are composed of atoms different kind. In chemical reactions, they can decompose to form simpler substances.

The difference between the concepts of "chemical element" and "simple substance"

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

When complex substances are decomposed, atoms can be released in a free state and combined to form simple substances. Simple substances are made up of atoms of one element. The difference between the concepts of "chemical element" and "simple substance" is also confirmed by the fact that one and the same element can form several simple substances. For example, atoms of the element oxygen can form diatomic oxygen molecules and triatomic ozone molecules. 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 of simple and complex substances:

Simple Substances that are made up of atoms of a single chemical element are called.

complex Substances that are made up of atoms of different chemical elements are called.

The difference between the concepts of "mixture" and "chemical compound"

Complex substances are often called chemical compounds.

Follow the link and view the experience of the interaction of simple substances of iron and sulfur.

Try to answer the questions:

1. What is the difference in the composition of the mixture from chemical compounds?

2. Compare the properties of mixtures and chemical compounds?

3. In what ways can a mixture and a chemical compound be divided into constituent components?

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

Comparative characteristics of mixtures and chemical connections

Tasks for fixing

I. Work with the machines

Trainer #1

Trainer №2

Trainer №3

II. Solve the task

From the proposed list of substances, write out separately simple and complex substances:

NaCl, H2SO4, K, S8, CO2, O3, H3PO4, N2, Fe.

Explain your choice, in each case.

III. Answer the questions

№1

How many simple substances are written in a series of formulas:

H2O, N2, O3, HNO3, P2O5, S, Fe, CO2, KOH.

№2

Both substances are complex:

A) C (coal) and S (sulfur);

B) CO2 (carbon dioxide) and H2O (water);

C) Fe (iron) and CH4 (methane);

D) H2SO4 (sulfuric acid) and H2 (hydrogen).

№3

Choose the correct statement:

Simple substances are made up of atoms of the same kind.

A) right

B) False

№4

Mixtures are characterized by

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 by a chemical reaction.

№5

For "chemical compounds" the following is characteristic:

A) Variable composition;

B) Substances in the composition of 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 is it about iron as a chemical element?

A) Iron is a metal that is attracted by a magnet;

B) Iron is part of the composition of rust;

C) Iron has a metallic luster;

D) Iron sulfide contains one iron atom.

№7

In which case is it 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 present in the air.

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.

Matter exists 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, air) contains two or more simple substances, and their atoms are not interconnected, then it is called not 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 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 characterize the ability of a substance to conduct electricity, determine the density of a substance, its hardness, etc. During 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).

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 called complex substances. 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 bonds with each other various types, 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 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 the interaction of 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, forming explosive mixtures with air, sulfur is a solid yellow color, capable of burning, and oxygen, 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 chemical substances, 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 due to 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.

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

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

An example is the simple substance oxygen. It includes molecules consisting of two atoms of the element Oxygen. Or, for example, the substance iron consists of crystals, including only atoms of the element Iron. Historically, it is customary to call a simple substance by the name of the element, the atoms of which are part of it. The structure of these compounds can be molecular and non-molecular.

Compounds include atoms different kind and upon decomposition may form two (or more) compounds. For example, water breaks down into oxygen and hydrogen. However, not every compound can be decomposed 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 principle of reverse reaction is applied. In other words, iron sulfide is obtained using the starting components.

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

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 passing into each other. different types simple substances formed by one chemical element may have different and different levels of chemical activity. So, for example, oxygen exhibits less activity than ozone, and the melting point of fullerene, for example, is lower than that of diamond.

Under 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 - solid bodies.

At temperatures close to room temperature, the five metals will assume a liquid or semi-liquid state. This is due to the fact that their melting point is almost equal to So, 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 definite, concrete meaning and exists in reality. The definition of "chemical element" is generally abstract, collective. In nature, elements are present in the form of free or chemically bonded atoms. At the same time, the characteristics of simple substances (sets of particles) and chemical elements (isolated atoms of a particular type) have their own characteristics.