Chemical formula is an image with symbols .

Signs of chemical elements

chemical sign or element chemical symbol is the first or two first letters of the Latin name of this element.

For example: Ferrum-Fe , cuprum-Cu , oxygenium-O etc.

Table 1: Information provided by the chemical mark

Intelligence	On the example of Cl
Element name	Chlorine
	Non-metal, halogen
One element	1 chlorine atom
(ar) given element	Ar(Cl) = 35.5
Absolute atomic mass chemical element m = Ar 1.66 10 -24 g = Ar 1.66 10 -27 kg	M (Cl) \u003d 35.5 1.66 10 -24 \u003d 58.9 10 -24 g

The name of a chemical sign in most cases is read as the name of a chemical element. For example, K - potassium, Ca - calcium, Mg - magnesium, Mn - manganese.

Cases where the name of the chemical mark is read differently are given in Table 2:

Name of the chemical element	chemical sign	The name of the chemical symbol (pronunciation)
Nitrogen	N	En
Hydrogen	H	Ash
Iron	Fe	Ferrum
Gold	Au	Aurum
Oxygen	O	ABOUT
Silicon	Si	Silicium
Copper	Cu	Cuprum
Tin	sn	Stanum
Mercury	hg	hydrargium
Lead	Pb	Plumbum
Sulfur	S	Es
Silver	Ag	Argentum
Carbon	C	Tse
Phosphorus	P	Pe

Chemical formulas of simple substances

The chemical formulas of most simple substances (all metals and many non-metals) are the signs of the corresponding chemical elements.

So substance iron And chemical element iron are labeled the same Fe .

If it has a molecular structure (exists in the form , then its formula is the chemical sign of the element with index bottom right, indicating number of atoms in a molecule: H2, O2, O 3, N 2, F2, Cl2, Br2, P4, S8.

Table 3: Information provided by the chemical mark

Intelligence	For example C
Substance name	Carbon (diamond, graphite, graphene, carbine)
Belonging of an element to a given class of chemical elements	Non-metal
One element atom	1 carbon atom
Relative atomic mass (ar) the element that makes up the substance	Ar(C)=12
Absolute atomic mass	M (C) \u003d 12 1.66 10-24 \u003d 19.93 10 -24 g
One substance	1 mole of carbon, i.e. 6.02 10 23 carbon atoms
	M(C) = Ar(C) = 12 g/mol

Chemical formulas of complex substances

The formula of a complex substance is compiled by writing the signs of the chemical elements of which this substance consists, indicating the number of atoms of each element in the molecule. In this case, as a rule, chemical elements are written in order of increasing electronegativity according to the following practice series:

Me , Si , B , Te , H , P , As , I , Se , C , S , Br , Cl , N , O , F

For example, H2O , CaSO4 , Al2O3 , CS2 , OF 2 , NaH.

The exception is:

• some compounds of nitrogen with hydrogen (for example, ammonia NH3 , hydrazine N 2H4 );
• salts of organic acids (for example, sodium formate HCOONa , calcium acetate (CH 3COO) 2Ca) ;
• hydrocarbons ( CH 4 , C 2 H 4 , C 2 H 2 ).

Chemical formulas of substances that exist in the form dimers (NO 2 , P2O 3 , P2O5, monovalent mercury salts, for example: HgCl , HgNO3 etc.), is written in the form N 2 O 4 ,P4 O 6 ,P4 O 10 ,Hg 2 Cl2,Hg 2 ( NO 3) 2 .

The number of atoms of a chemical element in a molecule and a complex ion is determined based on the concept valency or oxidation states and recorded index bottom right from the sign of each element (index 1 is omitted). This is based on the rule:

the algebraic sum of the oxidation states of all atoms in a molecule must be equal to zero (the molecules are electrically neutral), and in a complex ion, the charge of the ion.

For example:

2Al 3 + + 3SO 4 2- \u003d Al 2 (SO 4) 3

The same rule is used when determining the degree of oxidation of a chemical element according to the formula of a substance or complex. Usually it is an element that has several oxidation states. The oxidation states of the remaining elements forming the molecule or ion must be known.

The charge of a complex ion is the algebraic sum of the oxidation states of all the atoms that form the ion. Therefore, when determining the oxidation state of a chemical element in a complex ion, the ion itself is enclosed in brackets, and its charge is taken out of brackets.

When compiling formulas for valency a substance is represented as a compound consisting of two particles various types, whose valencies are known. Further enjoy rule:

in a molecule, the product of valence and the number of particles of one type must be equal to the product of valency and the number of particles of another type.

For example:

The number in front of a formula in a reaction equation is called coefficient. She indicates either number of molecules, or number of moles of a substance.

The coefficient before the chemical sign, indicates the number of atoms of a given chemical element, and in the case when the sign is a formula of a simple substance, the coefficient indicates either number of atoms, or the number of moles of this substance.

For example:

• 3 Fe- three iron atoms, 3 moles of iron atoms,
• 2 H- two hydrogen atoms, 2 mol hydrogen atoms,
• H2- one molecule of hydrogen, 1 mole of hydrogen.

The chemical formulas of many substances have been determined empirically, which is why they are called "empirical".

Table 4: Information provided by the chemical formula of a complex substance

Intelligence	For example C aCO3
Substance name	Calcium carbonate
Belonging of an element to a certain class of substances	Medium (normal) salt
One molecule of a substance	1 molecule of calcium carbonate
One mole of a substance	6.02 10 23 molecules CaCO3
Relative molecular weight of the substance (Mr)	Mr (CaCO3) \u003d Ar (Ca) + Ar (C) + 3Ar (O) \u003d 100
Molar mass of a substance (M)	M (CaCO3) = 100 g/mol
Absolute molecular weight of a substance (m)	M (CaCO3) = Mr (CaCO3) 1.66 10 -24 g = 1.66 10 -22 g
Qualitative composition (what chemical elements form a substance)	calcium, carbon, oxygen
The quantitative composition of the substance:
The number of atoms of each element in one molecule of a substance:	The calcium carbonate molecule is made up of 1 atom calcium, 1 atom carbon and 3 atoms oxygen.
The number of moles of each element in 1 mole of a substance:	In 1 mol CaCO 3(6.02 10 23 molecules) contains 1 mol(6.02 10 23 atoms) calcium, 1 mol(6.02 10 23 atoms) carbon and 3 mol(3 6.02 10 23 atoms) of the chemical element oxygen)
Mass composition of the substance:
The mass of each element in 1 mole of a substance:	1 mole of calcium carbonate (100g) contains chemical elements: 40g calcium, 12g carbon, 48g oxygen.
Mass fractions of chemical elements in a substance (composition of a substance in percent by weight):	Composition of calcium carbonate by mass: W (Ca) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (1 40) / 100 \u003d 0.4 (40%) W (C) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (1 12) / 100 \u003d 0.12 (12%) W (O) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (3 16) / 100 \u003d 0.48 (48%)
For a substance with an ionic structure (salts, acids, bases) - the formula of a substance gives information about the number of ions of each type in a molecule, their number and mass of ions in 1 mol of a substance:	Molecule CaCO 3 is made up of an ion Ca 2+ and ion CO 3 2- 1 mol ( 6.02 10 23 molecules) CaCO 3 contains 1 mol of Ca 2+ ions And 1 mole of ions CO 3 2-; 1 mole (100g) of calcium carbonate contains 40g ions Ca 2+ And 60g ions CO 3 2-
Molar volume of a substance under normal conditions (only for gases)

Graphic formulas

For more information about a substance use graphic formulas , which indicate the order in which atoms are connected in a molecule And valency of each element.

Graphic formulas of substances consisting of molecules, sometimes, to one degree or another, reflect the structure (structure) of these molecules, in these cases they can be called structural .

To draw up a graphical (structural) formula of a substance, you must:

• Determine the valence of all chemical elements that form a substance.
• Write down the signs of all chemical elements that form a substance, each in an amount equal to the number of atoms of a given element in a molecule.
• Connect the signs of chemical elements with dashes. Each line denotes a pair that makes a connection between chemical elements and therefore equally belongs to both elements.
• The number of dashes surrounding the sign of a chemical element must correspond to the valence of this chemical element.
• When formulating oxygen-containing acids and their salts, hydrogen atoms and metal atoms are bound to the acid-forming element through an oxygen atom.
• Oxygen atoms are connected to each other only when formulating peroxides.

Examples of graphic formulas:

Check information. It is necessary to check the accuracy of the facts and the reliability of the information presented in this article. There is a discussion on the talk page on the topic: Doubts about terminology. Chemical formula ... Wikipedia

A chemical formula is a reflection of information about the composition and structure of substances using chemical signs, numbers and separating brackets. Currently, the following types of chemical formulas are distinguished: The simplest formula. Can be obtained by experienced ... ... Wikipedia

A chemical formula is a reflection of information about the composition and structure of substances using chemical signs, numbers and separating brackets. Currently, the following types of chemical formulas are distinguished: The simplest formula. Can be obtained by experienced ... ... Wikipedia

A chemical formula is a reflection of information about the composition and structure of substances using chemical signs, numbers and separating brackets. Currently, the following types of chemical formulas are distinguished: The simplest formula. Can be obtained by experienced ... ... Wikipedia

A chemical formula is a reflection of information about the composition and structure of substances using chemical signs, numbers and separating brackets. Currently, the following types of chemical formulas are distinguished: The simplest formula. Can be obtained by experienced ... ... Wikipedia

Main article: Inorganic compounds List of inorganic compounds by element informational list of inorganic compounds provided in alphabetical order(according to the formula) for each substance, the hydrogen acids of the elements (with their ... ... Wikipedia

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A chemical equation (chemical reaction equation) is a conditional record of a chemical reaction using chemical formulas, numerical coefficients and mathematical symbols. The chemical reaction equation gives qualitative and quantitative ... ... Wikipedia

Chemical software are computer programs used in the field of chemistry. Contents 1 Chemical editors 2 Platforms 3 Literature ... Wikipedia

Books

• Brief Dictionary of Biochemical Terms, Kunizhev S.M. , The dictionary is intended for students of chemical and biological specialties of universities studying the course of general biochemistry, ecology and the basics of biotechnology, and can also be used in ... Category: Biology Publisher: VUZOVSKAYA KNIGA, Manufacturer:

Industrial methods for obtaining simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw material for its production. So, oxygen, which is available in a free state, is obtained in a physical way - by isolation from liquid air. Almost all hydrogen is in the form of compounds, so chemical methods are used to obtain it. In particular, decomposition reactions can be used. One of the ways to produce hydrogen is the reaction of decomposition of water by electric current.

The main industrial method for producing hydrogen is the reaction with water of methane, which is part of natural gas. It is carried out at a high temperature (it is easy to verify that when methane is passed even through boiling water, no reaction occurs):

CH 4 + 2H 2 0 \u003d CO 2 + 4H 2 - 165 kJ

In the laboratory, to obtain simple substances, not necessarily natural raw materials are used, but those initial substances are chosen from which it is easier to isolate the necessary substance. For example, in the laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water by electric current.

Hydrogen is usually produced in the laboratory by reacting zinc with hydrochloric acid.

In industry

1.Electrolysis of aqueous solutions of salts:

2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2

2.Passing water vapor over hot coke at approx. 1000°C:

H 2 O + C ⇄ H 2 + CO

3.From natural gas.

Steam conversion: CH 4 + H 2 O ⇄ CO + 3H 2 (1000 °C) catalytic oxidation oxygen: 2CH 4 + O 2 ⇄ 2CO + 4H 2

4. Cracking and reforming of hydrocarbons in the process of oil refining.

In the laboratory

1.Action of dilute acids on metals. To carry out such a reaction, zinc and hydrochloric acid are most often used:

Zn + 2HCl → ZnCl 2 + H 2

2.Interaction of calcium with water:

Ca + 2H 2 O → Ca (OH) 2 + H 2

3.Hydrolysis of hydrides:

NaH + H 2 O → NaOH + H 2

4.The action of alkalis on zinc or aluminum:

2Al + 2NaOH + 6H 2 O → 2Na + 3H 2 Zn + 2KOH + 2H 2 O → K 2 + H 2

5.With the help of electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is released at the cathode, for example:

2H 3 O + + 2e - → H 2 + 2H 2 O

• Bioreactor for hydrogen production

Physical Properties

Gaseous hydrogen can exist in two forms (modifications) - in the form of ortho - and para-hydrogen.

In the orthohydrogen molecule (mp −259.10 °C, bp −252.56 °C), the nuclear spins are directed in the same way (parallel), while in parahydrogen (mp −259.32 °C, t bp −252.89 °C) - opposite to each other (anti-parallel).

The allotropic forms of hydrogen can be separated by adsorption on active carbon at liquid nitrogen temperature. At very low temperatures the equilibrium between orthohydrogen and parahydrogen is almost entirely shifted towards the latter. At 80 K, the aspect ratio is approximately 1:1. Desorbed parahydrogen, when heated, transforms into orthohydrogen up to the formation of an equilibrium at room temperature mixtures (ortho-para: 75:25). Without a catalyst, the transformation occurs slowly, which makes it possible to study the properties of individual allotropic forms. The hydrogen molecule is diatomic - H₂. Under normal conditions, it is a colorless, odorless and tasteless gas. Hydrogen is the lightest gas, its density is many times less than that of air. Obviously, the smaller the mass of molecules, the higher their speed at the same temperature. As the lightest, hydrogen molecules move faster than the molecules of any other gas and thus can transfer heat from one body to another faster. It follows that hydrogen has the highest thermal conductivity among gaseous substances. Its thermal conductivity is about seven times higher than that of air.

Chemical properties

Hydrogen molecules H₂ are quite strong, and in order for hydrogen to react, a lot of energy must be expended: H 2 \u003d 2H - 432 kJ. Therefore, at ordinary temperatures, hydrogen reacts only with very active metals, for example, with calcium, forming calcium hydride: Ca + H 2 \u003d CaH 2 and with the only non-metal - fluorine, forming hydrogen fluoride: F 2 + H 2 \u003d 2HF With most metals and non-metals, hydrogen reacts at elevated temperatures or under other influences, such as lighting. It can “take away” oxygen from some oxides, for example: CuO + H 2 \u003d Cu + H 2 0 The written equation reflects the reduction reaction. Reduction reactions are called processes, as a result of which oxygen is taken away from the compound; Substances that take away oxygen are called reducing agents (they themselves oxidize). Further, another definition of the concepts of "oxidation" and "reduction" will be given. A this definition, historically the first, retains its significance at the present time, especially in organic chemistry. The reduction reaction is the opposite of the oxidation reaction. Both of these reactions always proceed simultaneously as one process: when one substance is oxidized (reduced), the other is necessarily reduced (oxidized) at the same time.

N 2 + 3H 2 → 2 NH 3

Forms with halogens hydrogen halides:

F 2 + H 2 → 2 HF, the reaction proceeds with an explosion in the dark and at any temperature, Cl 2 + H 2 → 2 HCl, the reaction proceeds with an explosion, only in the light.

It interacts with soot at strong heating:

C + 2H 2 → CH 4

Interaction with alkali and alkaline earth metals

Hydrogen forms with active metals hydrides:

Na + H 2 → 2 NaH Ca + H 2 → CaH 2 Mg + H 2 → MgH 2

hydrides- salty, solid substances, easily hydrolyzed:

CaH 2 + 2H 2 O → Ca(OH) 2 + 2H 2

Interaction with metal oxides (usually d-elements)

Oxides are reduced to metals:

CuO + H 2 → Cu + H 2 O Fe 2 O 3 + 3H 2 → 2 Fe + 3H 2 O WO 3 + 3H 2 → W + 3H 2 O

Hydrogenation of organic compounds

Under the action of hydrogen on unsaturated hydrocarbons in the presence of a nickel catalyst and elevated temperature, the reaction occurs hydrogenation:

CH 2 \u003d CH 2 + H 2 → CH 3 -CH 3

Hydrogen reduces aldehydes to alcohols:

CH 3 CHO + H 2 → C 2 H 5 OH.

Geochemistry of hydrogen

Hydrogen is the main building material of the universe. This is the most common element, and all elements are formed from it as a result of thermonuclear and nuclear reactions.

Free hydrogen H 2 is relatively rare in terrestrial gases, but in the form of water it takes an exceptionally important part in geochemical processes.

Hydrogen can be present in minerals in the form of ammonium ion, hydroxyl ion, and crystalline water.

In the atmosphere, hydrogen is continuously produced as a result of the decomposition of water by solar radiation. It migrates to the upper atmosphere and escapes into space.

Application

• Hydrogen energy

Atomic hydrogen is used for atomic hydrogen welding.

In the food industry, hydrogen is registered as food additive E949 as packing gas.

Features of circulation

Hydrogen, when mixed with air, forms an explosive mixture - the so-called detonating gas. This gas is most explosive when the volume ratio of hydrogen and oxygen is 2:1, or hydrogen and air is approximately 2:5, since air contains approximately 21% oxygen. Hydrogen is also flammable. Liquid hydrogen can cause severe frostbite if it comes into contact with the skin.

Explosive concentrations of hydrogen with oxygen occur from 4% to 96% by volume. When mixed with air from 4% to 75 (74)% by volume.

Use of hydrogen

In the chemical industry, hydrogen is used in the production of ammonia, soap and plastics. In the food industry, margarine is made from liquid vegetable oils using hydrogen. Hydrogen is very light and always rises in the air. Once airships and Balloons filled with hydrogen. But in the 30s. 20th century there were several terrible accidents when the airships exploded and burned. Nowadays, airships are filled with helium gas. Hydrogen is also used as rocket fuel. One day, hydrogen may be widely used as a fuel for cars and trucks. Hydrogen engines do not pollute environment and emit only water vapor (however, the very production of hydrogen leads to some environmental pollution). Our Sun is mostly made up of hydrogen. Solar heat and light are the result of the release of nuclear energy during the fusion of hydrogen nuclei.

Use of hydrogen as a fuel (economic efficiency)

The most important characteristic of substances used as fuel is their heat of combustion. From the course of general chemistry, it is known that the reaction of the interaction of hydrogen with oxygen occurs with the release of heat. If we take 1 mol H 2 (2 g) and 0.5 mol O 2 (16 g) under standard conditions and excite the reaction, then according to the equation

H 2 + 0.5 O 2 \u003d H 2 O

after completion of the reaction, 1 mol of H 2 O (18 g) is formed with an energy release of 285.8 kJ / mol (for comparison: the heat of combustion of acetylene is 1300 kJ / mol, propane - 2200 kJ / mol). 1 m³ of hydrogen weighs 89.8 g (44.9 mol). Therefore, to obtain 1 m³ of hydrogen, 12832.4 kJ of energy will be spent. Taking into account the fact that 1 kWh = 3600 kJ, we get 3.56 kWh of electricity. Knowing the tariff for 1 kWh of electricity and the cost of 1 m³ of gas, we can conclude that it is advisable to switch to hydrogen fuel.

For example, an experimental 3rd generation Honda FCX model with a 156-liter hydrogen tank (containing 3.12 kg of hydrogen at a pressure of 25 MPa) travels 355 km. Accordingly, 123.8 kWh is obtained from 3.12 kg H2. At 100 km, the energy consumption will be 36.97 kWh. Knowing the cost of electricity, the cost of gas or gasoline, their consumption for a car per 100 km, it is easy to calculate the negative economic effect of switching cars to hydrogen fuel. Let's say (Russia 2008), 10 cents per kWh of electricity leads to the fact that 1 m³ of hydrogen leads to a price of 35.6 cents, and taking into account the efficiency of water decomposition of 40-45 cents, the same amount of kWh from burning gasoline costs 12832.4 kJ/42000 kJ/0.7 kg/l*80 cents/l=34 cents at retail prices, while for hydrogen we calculated the ideal variant, without taking into account transportation, equipment depreciation, etc. For methane with a combustion energy of about 39 MJ per m³, the result will be two to four times lower due to the difference in price (1m³ for Ukraine costs $179, and for Europe $350). That is, the equivalent amount of methane will cost 10-20 cents.

However, we should not forget that when we burn hydrogen, we get clean water from which it was extracted. That is, we have a renewable storekeeper energy without harm to the environment, unlike gas or gasoline, which are primary sources of energy.

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Formulas for covalent bonds are fundamentally different from formulas for ionic bonds. The fact is that covalent compounds can be formed by the most different ways, therefore, as a result of the reaction, the appearance of various compounds is possible.

1. Empirical formula

IN empirical formula the elements that make up the molecule are indicated with the smallest integer ratios.

For example, C 2 H 6 O - the compound contains two carbon atoms, six hydrogen atoms and one oxygen atom.

2. Molecular formula

The molecular formula indicates what atoms the compound consists of and in what quantities these atoms are in it.

For example, for the compound C 2 H 6 O molecular formulas can be: C 4 H 12 O 2 ; C 6 H 18 O 3 ...

For a complete description of a covalent compound, the molecular formula is not enough:

As you can see, both compounds have the same molecular formula - C 2 H 6 O, but are completely different substances:

• dimethyl ether is used in refrigeration;
• ethyl alcohol is the basis of alcoholic beverages.

3. Structural formula

The structural formula serves to accurately determine the covalent compound, because, in addition to the elements in the compound and the number of atoms, it also shows link diagram connections.

The structural formula is electron point formula And Lewis formula.

4. Structural formula for water (H 2 O)

Consider the procedure for constructing a structural formula using the example of a water molecule.

I We build the connection frame

The atoms of the compound are arranged around the central atom. As the central atoms usually act: carbon, silicon, nitrogen, phosphorus, oxygen, sulfur.

II Find the sum of valence electrons of all atoms of the compound

For water: H 2 O \u003d (2 1 + 6) \u003d 8

There is one valence electron in the hydrogen atom, and 6 in the oxygen atom. Since there are two hydrogen atoms in the compound, then total number valence electrons of a water molecule will be equal to 8.

III Determine the number of covalent bonds in a water molecule

We determine by the formula: S=N-A, Where

S is the number of electrons shared in the molecule;

N- the sum of valence electrons corresponding to the completed external energy level of atoms in the compound:

N=2- for the hydrogen atom;

N = 8- for atoms of other elements

A is the sum of the valence electrons of all atoms in the compound.

N = 2 2 + 8 = 12

A = 2 1 +6 = 8

S=12 - 8=4

There are 4 shared electrons in a water molecule. Since a covalent bond consists of a pair of electrons, we get two covalent bonds.

IV We distribute joint electrons

There must be at least one bond between the central atom and the atoms that surround it. For a water molecule, there will be two such bonds for each hydrogen atom:

V Distribute the remaining electrons

Of the eight valence electrons, four have already been distributed. Where to "put" the remaining four electrons?

Each atom in a compound must have a full octet of electrons. For hydrogen, these are two electrons; for oxygen - 8.

The shared electrons are called binding.

The electron point formula and the Lewis formula clearly describe the structure of a covalent bond, but they are cumbersome and take up a lot of space. These shortcomings can be avoided by using concise structural formula, which indicates only the order of "following" links.

An example of a compressed structural formula:

• dimethyl ether - CH 3 OCH 3
• ethyl alcohol - C 2 H 5 OH

2.1. Chemical language and its parts

Mankind uses many different languages. Except natural languages(Japanese, English, Russian - more than 2.5 thousand in total), there are also artificial languages e.g. Esperanto. Among the artificial languages ​​are languages various Sciences. So, in chemistry, one uses its own, chemical language.
chemical language- a system of symbols and concepts designed for concise, concise and visual recording and transmission of chemical information.
A message written in most natural languages ​​is divided into sentences, sentences into words, and words into letters. If we call sentences, words and letters parts of the language, then we can distinguish similar parts in the chemical language (Table 2).

Table 2.Parts of the chemical language

It is impossible to master any language at once, this also applies to the chemical language. Therefore, for now, you will only get acquainted with the basics of this language: learn some "letters", learn to understand the meaning of "words" and "sentences". At the end of this chapter, you will be introduced to titles chemicals are an integral part of the chemical language. As you study chemistry, your knowledge of the chemical language will expand and deepen.

CHEMICAL LANGUAGE.
1. What artificial languages ​​do you know (except those named in the text of the textbook)?
2. How do natural languages ​​differ from artificial ones?
3. Do you think it is possible to do without the use of chemical language when describing chemical phenomena? If not, why not? If so, what would be the advantages and disadvantages of such a description?

2.2. Symbols of chemical elements

The symbol for a chemical element denotes the element itself or one atom of that element.
Each such character is an abbreviation Latin name chemical element, consisting of one or two letters of the Latin alphabet (for the Latin alphabet, see Appendix 1). The symbol is capitalized. Symbols, as well as Russian and Latin names of some elements, are given in Table 3. Information about the origin of Latin names is also given there. There is no general rule for the pronunciation of symbols, therefore Table 3 also shows the "reading" of a symbol, that is, how this symbol is read in a chemical formula.

It is impossible to replace the name of an element with a symbol in oral speech, and in handwritten or printed texts this is allowed, but not recommended. Currently, 110 chemical elements are known, 109 of them have names and symbols approved by the International Union of Pure and Applied Chemistry (IUPAC).
Table 3 provides information on only 33 elements. These are the elements that you will encounter first when studying chemistry. Russian names (in alphabetical order) and symbols of all elements are given in Appendix 2.

Table 3Names and symbols of some chemical elements

Name
	latin		Writing
-	Writing	Origin	-	-
Nitrogen	N itrogenium	From Greek. "giving birth to saltpeter"		"en"
Aluminum	Al uminium	From lat. "alum"		"aluminum"
Argon	Ar gon	From Greek. "inactive"		"argon"
Barium	Ba rium	From Greek. " heavy"		"barium"
Bor	B orum	From Arabic. "white mineral"		"bor"
Bromine	Br omum	From Greek. "malodorous"		"bromine"
Hydrogen	H hydrogenium	From Greek. "giving birth to water"		"ash"
Helium	He lium	From Greek. " Sun"		"helium"
Iron	Fe rrum	From lat. "sword"		"ferrum"
Gold	Au rum	From lat. "burning"		"aurum"
Iodine	I odum	From Greek. " violet"		" iodine"
Potassium	K alium	From Arabic. "lye"		"potassium"
Calcium	Ca lcium	From lat. "limestone"		"calcium"
Oxygen	O xygenium	From Greek. "producer of acids"		" O"
Silicon	Si licium	From lat. "flint"		"silicium"
Krypton	kr ypton	From Greek. "hidden"		"krypton"
Magnesium	M a g nesium	From the name peninsulas of Magnesia		"magnesium"
Manganese	M a n ganum	From Greek. "purifying"		"manganese"
Copper	Cu prum	From Greek. name O. Cyprus		"cuprum"
Sodium	Na trium	From Arabic, "detergent"		"sodium"
Neon	Ne on	From Greek. " new"		"neon"
Nickel	Ni colum	From him. "copper of St. Nicholas"		"nickel"
Mercury	H ydrar g yrum	Lat. "liquid silver"		"hydrargyrum"
Lead	P lum b um	From lat. the name of the alloy of lead and tin.		"plumbum"
Sulfur	S sulfur	From Sanskrit "flammable powder"		"es"
Silver	A r g entum	From Greek. " light"		"argentum"
Carbon	C arboneum	From lat. " coal"		"ce"
Phosphorus	P hosphorus	From Greek. "bringer of light"		"pe"
Fluorine	F luorum	From lat. verb "to flow"		"fluorine"
Chlorine	Cl orum	From Greek. "greenish"		"chlorine"
Chromium	C h r omium	From Greek. " dye"		"chrome"
Cesium	C ae s ium	From lat. "sky blue"		"cesium"
Zinc	Z i n cum	From him. "tin"		"zinc"

2.3. Chemical formulas

Used to refer to chemicals chemical formulas.

For molecular substances, the chemical formula can also denote one molecule of this substance.
Information about a substance can be different, so there are different types of chemical formulas.
Depending on the completeness of information, chemical formulas are divided into four main types: protozoa, molecular, structural And spatial.

Subscripts in the simplest formula do not have a common divisor.
Index "1" is not put in formulas.
Examples of the simplest formulas: water - H 2 O, oxygen - O, sulfur - S, phosphorus oxide - P 2 O 5, butane - C 2 H 5, phosphoric acid - H 3 PO 4, sodium chloride (table salt) - NaCl.
The simplest formula of water (H 2 O) shows that the water contains the element hydrogen(H) and element oxygen(O), and in any portion (a portion is a part of something that can be divided without losing its properties.) of water, the number of hydrogen atoms is twice the number of oxygen atoms.
Number of particles, including number of atoms, denoted by the Latin letter N. Denoting the number of hydrogen atoms - N H , and the number of oxygen atoms is N O , we can write that

Or N H: N O=2:1.

The simplest formula of phosphoric acid (H 3 PO 4) shows that phosphoric acid contains atoms hydrogen, atoms phosphorus and atoms oxygen, and the ratio of the numbers of atoms of these elements in any portion of phosphoric acid is 3:1:4, that is

NH: N P: N O=3:1:4.

The simplest formula can be drawn up for any individual chemical, and for a molecular substance, in addition, it can be composed molecular formula.

Examples of molecular formulas: water - H 2 O, oxygen - O 2, sulfur - S 8, phosphorus oxide - P 4 O 10, butane - C 4 H 10, phosphoric acid - H 3 PO 4.

Nonmolecular substances do not have molecular formulas.

The sequence of writing the symbols of elements in the simplest and molecular formulas is determined by the rules of the chemical language, which you will learn as you study chemistry. The sequence of characters does not affect the information conveyed by these formulas.

Of the signs reflecting the structure of substances, we will use so far only valence stroke("dash"). This sign shows the presence between the atoms of the so-called covalent bond(what kind of connection is this and what are its features, you will soon find out).

In the water molecule, the oxygen atom is connected by simple (single) bonds with two hydrogen atoms, and the hydrogen atoms are not connected to each other. This is clearly shown by the structural formula of water.

Another example: the sulfur molecule S 8 . In this molecule, 8 sulfur atoms form an eight-membered cycle, in which each sulfur atom is connected to two other atoms by simple bonds. Compare the structural formula of sulfur with the three-dimensional model of its molecule shown in fig. 3. Please note that the structural formula of sulfur does not convey the shape of its molecule, but only shows the sequence of connecting atoms by covalent bonds.

The structural formula of phosphoric acid shows that in the molecule of this substance one of the four oxygen atoms is connected only with the phosphorus atom by a double bond, and the phosphorus atom, in turn, is connected with three more oxygen atoms by simple bonds. Each of these three oxygen atoms, in addition, is connected by a simple bond with one of the three hydrogen atoms present in the molecule./p>

Compare the following three-dimensional model of the methane molecule with its spatial, structural and molecular formula:

In the spatial formula of methane, wedge-shaped valence strokes, as if in perspective, show which of the hydrogen atoms is "closer to us" and which is "farther from us".

Sometimes the spatial formula indicates the bond lengths and the values ​​of the angles between the bonds in the molecule, as shown in the example of the water molecule.

Nonmolecular substances do not contain molecules. For the convenience of carrying out chemical calculations in a nonmolecular substance, the so-called formula unit.

Examples of the composition of the formula units of some substances: 1) silicon dioxide (quartz sand, quartz) SiO 2 - the formula unit consists of one silicon atom and two oxygen atoms; 2) sodium chloride (common salt) NaCl - the formula unit consists of one sodium atom and one chlorine atom; 3) iron Fe - a formula unit consists of one iron atom. Like a molecule, a formula unit is the smallest portion of a substance that retains its chemical properties.

Table 4

Information Conveyed by Different Types of Formulas

Formula type	The information passed by the formula.
Protozoa Molecular Structural Spatial		Atoms of which elements make up a substance. The ratios between the numbers of atoms of these elements. The number of atoms of each of the elements in the molecule. Types of chemical bonds. The sequence of connecting atoms by covalent bonds. Multiplicity of covalent bonds. Mutual arrangement atoms in space. Bond lengths and bond angles (if specified).

Let us now consider, with examples, what information formulas of different types give us.

1. Substance: acetic acid. The simplest formula is CH 2 O, the molecular formula is C 2 H 4 O 2, the structural formula

The simplest formula tells us that
1) in the composition acetic acid includes carbon, hydrogen and oxygen;
2) in this substance, the number of carbon atoms is related to the number of hydrogen atoms and to the number of oxygen atoms, as 1:2:1, that is N H: N C: N O = 1:2:1.
Molecular formula adds that
3) in a molecule of acetic acid - 2 carbon atoms, 4 hydrogen atoms and 2 oxygen atoms.
Structural formula adds that
4, 5) in the molecule, two carbon atoms are linked by a single bond; one of them, in addition, is associated with three hydrogen atoms, with each single bond, and the other with two oxygen atoms, with one double bond, and with the other a single bond; the last oxygen atom is also linked by a simple bond to the fourth hydrogen atom.

2. Substance: sodium chloride. The simplest formula is NaCl.
1) Sodium chloride contains sodium and chlorine.
2) In this substance, the number of sodium atoms is equal to the number of chlorine atoms.

3. Substance: iron. The simplest formula is Fe.
1) The composition of this substance includes only iron, that is, it is a simple substance.

4. Substance: trimetaphosphoric acid . The simplest formula is HPO 3, the molecular formula is H 3 P 3 O 9, the structural formula

1) The composition of trimetaphosphoric acid includes hydrogen, phosphorus and oxygen.
2) N H: N P: N O = 1:1:3.
3) A molecule consists of three hydrogen atoms, three phosphorus atoms and nine oxygen atoms.
4, 5) Three phosphorus atoms and three oxygen atoms, alternating, form a six-membered cycle. All links in the cycle are simple. Each phosphorus atom, in addition, is associated with two more oxygen atoms, with one - a double bond, and the other - a simple one. Each of the three oxygen atoms linked by simple bonds to phosphorus atoms is also linked by a simple bond to a hydrogen atom.

Phosphoric acid - H 3 PO 4(another name is phosphoric acid) is a transparent colorless crystalline substance of a molecular structure, melting at 42 o C. This substance is very soluble in water and even absorbs water vapor from the air (hygroscopically). Phosphoric acid is produced in large quantities and is used primarily in the production of phosphate fertilizers, as well as in the chemical industry, in the production of matches, and even in construction. In addition, phosphoric acid is used in the manufacture of cement in dental technology, is part of many medicines. This acid is cheap enough that in some countries, such as the United States, very pure phosphoric acid, highly diluted with water, is added to refreshments to replace expensive citric acid.

Methane - CH 4. If you have a gas stove at home, then you come across this substance every day: the natural gas that burns in the burners of your stove is 95% methane. Methane is a colorless and odorless gas with a boiling point of -161 o C. When mixed with air, it is explosive, which explains the explosions and fires that sometimes occur in coal mines (another name for methane is firedamp). The third name of methane - swamp gas - is due to the fact that bubbles of this particular gas rise from the bottom of swamps, where it is formed as a result of the activity of certain bacteria. In industry, methane is used as a fuel and raw material for the production of other substances. Methane is the simplest hydrocarbon. This class of substances also includes ethane (C 2 H 6), propane (C 3 H 8), ethylene (C 2 H 4), acetylene (C 2 H 2) and many other substances.

Table 5.Examples of formulas of different types for some substances-