Dictionary of chemical formulas. Chemical formulas of substances Information provided by the chemical formula of a substance

What is the chemical formula? Every science has its own notation system. Chemistry is no exception in this regard. You already know that symbols derived from the Latin names of the elements are used to designate chemical elements. Chemical elements are capable of forming both simple and complex substances, the composition of which can be expressed chemical formula. To write the chemical formula of a simple substance, you need to write down the symbol of the chemical element that forms the simple substance, and write down the number at the bottom right showing the number of its atoms. This figure is called index. For example, the chemical formula of oxygen is O2. The number 2 after the oxygen symbol is an index indicating that the oxygen molecule consists of two atoms of the element oxygen. Index - a number showing the number of atoms of a certain type in a chemical formula To write the chemical formula of a complex substance, you need to know which atoms of elements it consists of (qualitative composition), and the number of atoms of each element (quantitative composition). For example, the chemical formula of baking soda is NaHCO3. The composition of this substance includes atoms of sodium, hydrogen, carbon, oxygen - this is its qualitative composition. There are one sodium, hydrogen, and carbon atoms each, and three oxygen atoms. This is the quantitative composition of soda High-quality composition a substance shows which atoms of elements are included in its composition Quantitative composition a substance shows the number of atoms that make up it Chemical formula– conventional recording of the composition of a substance using chemical symbols and indices Please note that if a chemical formula contains only one atom of one type, the subscript 1 is not used. For example, the formula for carbon dioxide is written as follows: CO2, not C1O2.

How to understand chemical formulas correctly?

When writing chemical formulas, you often come across numbers that are written before the chemical formula. For example, 2Na, or 5O2. What do these numbers mean and what are they for? The numbers written before a chemical formula are called coefficients. Coefficients show the total number of particles of a substance: atoms, molecules, ions. For example, the notation 2Na represents two sodium atoms. The notation 5O2 means five/ Coefficient - a number that shows the total number of particles. The coefficient is written before the chemical formula of the substance of oxygen molecules. Please note that molecules cannot consist of one atom, the minimum number of atoms in a molecule is two. So the entries are: 2H, 4P stand for two hydrogen atoms and four phosphorus atoms, respectively. Record 2H2 denotes two hydrogen molecules containing two atoms of the element hydrogen. Record 4S8– denotes four sulfur molecules, each containing eight atoms of the element sulfur. A similar system of notation for the number of particles is used for ions. Record 5K+ stands for five potassium ions. It is worth noting that ions can be formed not only by an atom of one element. Ions formed by atoms of one chemical element are called simple: Li+, N3−. Ions formed by several chemical elements are called complex: OH⎺, SO4 2−. Note that the charge of an ion is indicated by a superscript. What will the entry mean? 2NaCl? If the answer to this question is two molecules of table salt, then the answer is not correct. Table salt, or sodium chloride, has an ionic crystal lattice, that is, it is an ionic compound and consists of ions Na+ and Cl⎺. A pair of these ions is called formula unit of a substance. Thus, the notation 2NaCl means two formula units sodium chloride. The term formula unit is also used for substances of atomic structure. Formula unit– the smallest particle of a substance of non-molecular structure Ionic compounds are just as electrically neutral as molecular ones. This means that the positive charge of the cations is completely balanced by the negative charge of the anions. For example, what is the formula unit of a substance consisting of ions Ag+ and PO4 3−? Obviously, to compensate for the negative charge of the ion (charge –3), it is necessary to have a charge of +3. Taking into account the fact that the silver cation has a charge of +1, then three such cations are needed. This means the formula unit (formula) of a given substance is Ag3PO4. Thus, using the symbols of chemical elements, indices and coefficients, it is possible to clearly compose the chemical formula of a substance, which will provide information about both the qualitative and quantitative composition of the substance. Finally, let's look at how to correctly pronounce chemical formulas. For example, record 3Ca2+ pronounced: "three calcium ions two plus" or "three calcium ions with charge two plus." Record 4HCl, pronounced “four molecules of ash chlorine.” Record 2NaCl, pronounced like "two formula units of sodium chloride."

Law of constancy of the composition of matter

The same chemical compound can be prepared in different ways. For example, carbon dioxide CO2, is formed by burning fuels: coal, natural gas. Fruits contain a lot of glucose. During long-term storage, fruits begin to deteriorate and a process called glucose fermentation begins, which results in the release of carbon dioxide. Carbon dioxide is also formed when rocks such as chalk, marble, and limestone are heated. Chemical reactions are completely different, but the substance formed as a result of their occurrence has the same qualitative and quantitative composition – CO2. This pattern applies mainly to substances of molecular structure. In the case of substances of non-molecular structure, there may be cases when the composition of the substance depends on the methods of its preparation. The law of constancy of the composition of substances of molecular structure: the composition of a complex substance is always the same and does not depend on the method of its preparation Conclusions from an article on the topic Chemical formulas of substances

Index– a number showing the number of atoms of a certain type in a chemical formula
The qualitative composition of a substance shows which atoms of elements are included in its composition
The quantitative composition of a substance shows the number of atoms that are included in its composition
Chemical formula - a conventional recording of the composition of a substance using chemical symbols and indices (if necessary)
Coefficient– a number that shows the total number of particles. The coefficient is written before the chemical formula of the substance
Formula unit– the smallest particle of a substance of atomic or ionic structure

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The lesson is devoted to learning the rules of drawing up and reading chemical formulas of substances. You will learn what information the chemical formula of a substance provides and how to compose a chemical formula based on data on the mass fractions of chemical elements.

Topic: Initial chemical ideas

Lesson: Chemical formula of a substance

Chemical formulas are used to designate substances.

Chemical formula is a conventional notation of the composition of a substance using chemical signs And indexes.

Using the indices of Y.Ya. Berzelius proposed to designate the number of atoms of a chemical element in a molecule of a substance. For example: a water molecule contains two hydrogen atoms and one oxygen atom - H 2 O (2 - index). Carbon dioxide contains one carbon atom and two oxygen atoms - CO 2. An index equal to one is not written.

The number before the formula of a substance is called coefficient and indicates the number of molecules of a given substance. For example, 4H 2 O - 4 water molecules. Four water molecules contain 8 hydrogen atoms and 4 oxygen atoms.

Using carbon dioxide CO 2 as an example, let us consider what information about a substance can be obtained from its chemical formula.

Table 1.

Based on the chemical formula, you can calculate the mass fractions of chemical elements in a substance; this will be discussed in the material of the next lesson.

Chemical formulas are derived based on data obtained experimentally. If the elements in a substance and the relative substance are known, one can find the number of atoms of each element in the molecule.

Example. It is known that the relative molecular weight of carbon dioxide is 44. The mass fraction of oxygen in this substance is 0.727 (72.7%), the rest is carbon. Let's make up the chemical formula of carbon dioxide. To do this you need:

1. determine the mass per share of oxygen atoms in the molecule:

44*0.727=32 (relative units);

2. determine the number of oxygen atoms, knowing that the relative atomic mass of oxygen is 16:

3. determine the mass per share of carbon atoms:

44-32=12 (relative units);

4. determine the number of carbon atoms, knowing that the relative atomic mass of carbon is 12:

5. create the formula for carbon dioxide: CO 2.

1. Collection of problems and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry, 8th grade” / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M.: AST: Astrel, 2006. (p.26-28)

2. Ushakova O.V. Chemistry workbook: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. 8th grade” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006. (p. 32-34)

3. Chemistry: 8th grade: textbook. for general education institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005.(§14)

4. Chemistry: inorg. chemistry: textbook. for 8th grade. general education institutions / G.E. Rudzitis, Fyu Feldman. - M.: Education, OJSC “Moscow Textbooks”, 2009. (§10)

5. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed.V.A. Volodin, Ved. scientific ed. I. Leenson. - M.: Avanta+, 2003.

Additional web resources

1. Unified collection of digital educational resources ().

2. Electronic version of the journal “Chemistry and Life” ().

Homework

1. p.77 No. 3 from the textbook “Chemistry: 8th grade” (P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005).

2. With. 32-34 No. 3,4,6,7 from the Workbook in Chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. 8th grade” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006.

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Books

Japanese-English-Russian dictionary for installation of industrial equipment. About 8,000 terms, Popova I.S.. The dictionary is intended for a wide range of users and primarily for translators and technical…
A brief dictionary of biochemical terms, Kunizhev S.M.. The dictionary is intended for students of chemical and biological specialties at universities,…

Chemical formulas are used to designate substances.

Chemical formula is a conventional notation of the composition of a substance using chemical symbols and indices.

Using the indices of Y.Ya. Berzelius proposed to designate the number of atoms of a chemical element in a molecule of a substance. For example: a water molecule contains two hydrogen atoms and one oxygen atom - H 2 O (2 is the index). Carbon dioxide contains one carbon atom and two oxygen atoms – CO 2 . An index equal to one is not written.

The number before the formula of a substance is called a coefficient and indicates the number of molecules of a given substance. For example, 4H 2 O – 4 water molecules. Four water molecules contain 8 hydrogen atoms and 4 oxygen atoms.

Information provided by the chemical formula of a substance

Using carbon dioxide CO2 as an example, let’s consider what information about a substance can be obtained from its chemical formula.

Based on the chemical formula, you can calculate the mass fractions of chemical elements in a substance; this will be discussed in the material of the next lesson.

Derivation of the chemical formula of a substance

Chemical formulas are derived based on data obtained experimentally. If the mass fractions of elements in a substance and the relative molecular weight of the substance are known, the number of atoms of each element in the molecule can be found.

Example. It is known that the relative molecular weight of carbon dioxide is 44. The mass fraction of oxygen in this substance is 0.727 (72.7%), the rest is carbon. Let's make up the chemical formula of carbon dioxide. To do this you need:

1. determine the mass per share of oxygen atoms in the molecule:

44*0.727=32 (relative units);

2. determine the number of oxygen atoms, knowing that the relative atomic mass of oxygen is 16:

3. determine the mass per share of carbon atoms:

44-32=12 (relative units);

4. determine the number of carbon atoms, knowing that the relative atomic mass of carbon is 12:

5. create the formula for carbon dioxide: CO 2.

Literature

3. Chemistry: 8th grade: textbook. for general education institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005.(§14)

4. Chemistry: inorg. chemistry: textbook. for 8th grade. general education institutions / G.E. Rudzitis, Fyu Feldman. – M.: Education, OJSC “Moscow Textbooks”, 2009. (§10)

5. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed.V.A. Volodin, Ved. scientific ed. I. Leenson. – M.: Avanta, 2003.

1. What amount of calcium oxide substance has a mass of 140 g? (CaO)
2. Calculate the mass and volume of carbon dioxide Co2 with an amount of substance of 2.2 mol.
Answer the questions.
3. The position of metals in PSCE, features of their electronic structure. General physical properties of metal. Create electronic formulas for calcium, lithium and aluminum.

We urgently need answers to these questions!

Answer the questions.Yes/No
1. The composition of the bases must include a hydroxy group??? Not really
2.Water-soluble hydroxides are called alkalis??? Not really
3. The number of hydroxy groups per one atom of a metal element is twice the valency of this element??? Not really
4. Alkalis are part of almost all minerals on Earth??? Not really
5. In the presence of alkalis, phenolphthalein becomes colorless??? Not really
6. Sodium oxide reacts with water to form an alkali??? Not really
7. Alkalis can be obtained through the interaction of the most active metals with water??? Not really
8. Does cuprum(2) oxide actively interact with water? Not really
9.Aluminum hydroxide is an alkali? Not really
10. Does methyl orange turn red in the presence of alkalis? Not really
11.Zinc hydroxide is an amphoteric hydroxide? Not really
12.Barium hydroxide has the formula Ba(OH)3? Not really

Before answering a question, be sure to write the number of the question you are answering. Thank you very much in advance!

Characterize the chemical element C according to plan:

a) position in PSHE - period, group, number of energy levels, number of electrons at the last level;
b) the formula of the higher oxide, its character;
c) the formula of the higher hydroxide, its character;
d) formula and name of a volatile hydrogen compound.

Which of the following substances will sodium oxide react with?

1) NO
2) NaCl
3) H2
4) H2O
In the list of substances, acid oxides include:
1) Na2O, N2O5, CaO
2) N2O5, SO2, SiO2
3) CaO, SiO2, SO3
4) CuO, CO2, MgO
Which of the following substances will nitric oxide (V) interact with?
1) KOH;
2) HCl;
3) NaCl;
4) O2
What chemical properties are characteristic of calcium oxide?
Choose the correct answer.
1) gas under normal conditions;
2) a solid, white substance;
3) black solid;
4) colorless volatile liquid.
A5. What is the name of the substance SO3?
1) sulfur oxide;
2) sulfur oxide (II)
3) sulfur oxide (VI)
4) sulfur oxide (IV).
A6. Oxides are formed:
1) during the combustion of simple and complex substances;
2) during the decomposition of soluble bases;
3) only when burning complex substances;
4) during the decomposition of silicic acid.
Which of the following substances will zinc oxide react with?
1) H2O
2) HCl
3) O2
4) Al2O3
Match the formula with the name of the corresponding oxide:
Formula
Oxide name
A) CuO
B) Na2O
B) Mn2O7
D) SO3
1) copper (II) oxide
2) sodium oxide
3) sulfur oxide (VI)
4) manganese (II) oxide
5) potassium oxide
6) manganese (VII) oxide

Establish a correspondence between the formula of the oxide and the reagents with each of which it can interact.
Formula
Reagents
A) Na2O
B) CO2
B) Al2O3
1) HCl, Na(OH), K2CO3
2) H2O, CaO, Ca(OH)2
3) CO2, H2SO4, H2O
4) CaCl2, SiO2, K2O

Vanadium(V) oxide is produced by burning metal powder in oxygen. Calculate the mass of vanadium required to obtain an oxide weighing 50 g.

Another task number 3 in the test that I don’t understand. The chemical formulas are given: a) MnO c) Fe e) 3SO3 g)

I presented small letters as numbers: z - 3; z - 2.

Complete task 1,2,3..., selecting one or more correct answers under the letters a, b, c...

1. What letter represents two chlorine molecules?

2. Which entry reads magnesium-chlorine-two?

3. Choose simple substances.

4. Select formulas of substances only with index "1".

5. Select the formula of complex substances only with coefficient “1”.

6. Find formulas with chemical elements of side subgroups of the Periodic System D.I. Mendeleev.

7. Find formulas with chemical elements of the third period.

8 Identify a complex substance whose relative molecular weight is 170.

And help me solve this extra. exercise:

Using the data from task 3, answer the questions.

Which formulas contain the same number of atoms of the same chemical element?