Simple and complex substances. Nomenclature

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.

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 molecules O 3 and has its own 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, sodium chloride NaCl can be formed from simple substances - metallic sodium Na and gaseous chlorine Cl. The physical and chemical properties of NaCl differ from the properties of Na and Cl 2.

In nature, as a rule, there are not 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).

The most important differences between mixtures and chemical compounds:

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

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. The difference between chemical compounds and 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 certain substance is burned in oxygen, sulfur (IV) oxide, nitrogen and water are obtained. 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.

Simple and complex substances. Chemical element

About atoms and chemical elements

In chemistry, in addition to the terms “atom” and “molecule,” the concept “element” is often used. What do these concepts have in common and how do they 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 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 distinguish between simple substances 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 O3 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.

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. 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– the molecules of such substances consist of atoms of different types. 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 – is a colorless gas necessary for breathing and supporting combustion. The smallest particle of 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. Therefore, when we talk about the composition of any chemical compounds, it should be understood that these compounds do not contain simple substances, but atoms of a 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 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 to simple and complex substances:

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

Complex are called substances 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.

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

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 the formation of a mixture or chemical compound?

Comparative characteristics of mixtures and chemicals connections

Tasks for consolidation

I. Work with simulators

Simulator No. 1

Simulator No. 2

Simulator No. 3

II. Solve the task

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

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);

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

D) H2SO4 (sulfuric acid) and H2 (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 iron as a 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.

When studying the material in the previous paragraphs, you have already become acquainted with some substances. For example, a molecule of hydrogen gas 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 known to you include: oxygen, graphite, sulfur, nitrogen, all metals: iron, copper, aluminum, gold, etc. Sulfur consists only of atoms of the chemical element sulfur, while graphite consists of atoms of the chemical element carbon.

It is necessary to clearly distinguish between concepts "chemical element" And "simple matter". 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, the chemical element (carbon) and the simple substance (diamond) are called differently. Often a chemical element and its corresponding simple substance are named the same. For example, the element oxygen corresponds to a simple substance - oxygen.

It is necessary to learn how to distinguish between where we are talking about an element and where about a substance! 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 the simple substance oxygen.

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

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

Nonmetals 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 is bromine, a brownish-red liquid.

If you draw a conventional line from the chemical element boron to the chemical element astatine, then in the long version of the Periodic System there are non-metallic elements above the line, and below it - metal. In the short version of the Periodic Table, there are non-metallic elements below this line, and both metallic and non-metallic elements 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 Table. This division is arbitrary, since all elements in one way or another exhibit both metallic and non-metallic properties, but in most cases this distribution corresponds to reality.

Complex 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 containing atoms of various types

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

Complex substances are usually divided into two groups: inorganic substances and their derivatives and organic substances and their derivatives. For example, rock salt is an inorganic substance, and the starch contained in potatoes is an organic substance.

Types of structure of substances

Based on the type of particles that make up the substances, substances are divided into substances molecular and non-molecular structure.

The substance may contain various structural particles, such as atoms, molecules, ions. Consequently, there are three types of substances: substances of atomic, ionic and molecular structure. Substances of different types of structure will have different properties.

Substances of atomic structure

An example of substances of atomic structure are substances formed by the element carbon: graphite and diamond. These substances contain only carbon atoms, but the properties of these substances are very different. Graphite– a fragile, easily exfoliating substance of gray-black color. Diamond– transparent, one of the hardest minerals on the planet. Why do substances consisting of the same type of atom have different properties? It's all about the structure of these substances. The carbon atoms in graphite and diamond join together in different ways. Substances of atomic structure have high boiling and melting points, are usually insoluble in water, and nonvolatile.

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 includes 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 molecular structure have low boiling and melting points, are usually fragile, and do not conduct electricity.

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 we can see, NaCl consists of ions Na+ and Cl⎺, alternating in certain places (nodes) of the crystal lattice. Substances with an ionic structure have high melting and boiling points, are fragile, are usually 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 specific 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 bonded atoms, that is, simple and complex substances.

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

When we talk about a material or component of a mixture - for example, a flask is filled with chlorine gas, 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, the substance contains phosphorus, the 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 (a collection of particles) and the properties (characteristics) of a chemical element (an isolated atom of a certain type), see the table below:

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

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

For example, in a glass of tea you can add one spoon 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 no mixture.

The components of the mixture retain their physical and chemical properties. For example, if you mix iron powder with sulfur, 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 has neither the properties of iron nor sulfur, but has a set of its own properties. In connection FeS iron and sulfur are bound to each other, and they cannot be separated using the methods used to separate mixtures.

Thus, substances can be classified according to several parameters:

Conclusions from an article on the topic Simple and complex substances

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