Chemical formula h2. Chemical names and formulas of substances

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Chemical formula is an image using symbols.

Chemical element signs

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

For example: FerrumFe , Cuprum –Cu , OxygeniumO etc.

Table 1: Information provided by a chemical sign

Intelligence	Using the example of Cl
Item name	Chlorine
	Non-metal, halogen
One element	1 chlorine atom
(Ar) of this element	Ar(Cl) = 35.5
Absolute atomic mass of a chemical element m = Ar 1.66 10 -24 g = Ar 1.66 10 -27 kg	M (Cl) = 35.5 1.66 10 -24 = 58.9 10 -24 g

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

Cases when the name of a chemical symbol is read differently are given in Table 2:

Chemical element name	Chemical sign	Chemical symbol name (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 iron substance And chemical element iron are designated the same - Fe .

If it has a molecular structure (exists in the form , then its formula is the chemical symbol of the element with index bottom right indicating number of atoms in a molecule: H 2, O2, O 3, N 2, F 2, Cl2, BR 2, P 4, S 8.

Table 3: Information provided by a chemical sign

Intelligence	Using C as an example
Substance name	Carbon (diamond, graphite, graphene, carbyne)
Belonging of an element to a given class of chemical elements	Non-metal
One atom of an element	1 carbon atom
Relative atomic mass (Ar) element that forms a substance	Ar(C) = 12
Absolute atomic mass	M(C) = 12 1.66 10-24 = 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 prepared by writing down the signs of the chemical elements of which the substance is composed, 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 in accordance with the following practical series:

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

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

The exceptions are:

some compounds of nitrogen with hydrogen (for example, ammonia NH 3 , hydrazine N 2H 4 );
salts of organic acids (for example, sodium formate HCOONa , calcium acetate (CH 3COO) 2Ca) ;
hydrocarbons ( CH 4 , C2H4 , C2H2 ).

Chemical formulas of substances existing in the form dimers (NO 2 , P2O 3 , P2O5, salts of monovalent mercury, for example: HgCl , HgNO3 etc.), written in the form N 2 O4,P 4 O6,P 4 O 10Hg 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 is recorded index lower right from the sign of each element (index 1 is omitted). In this case, they proceed from 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- =Al 2 (SO 4) 3

The same rule is used when determining the oxidation state of a chemical element using the formula of a substance or complex. It is usually 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 placed 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 of different types, the valencies of which are known. Next they use rule:

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

For example:

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

The coefficient before the chemical symbol, indicates number of atoms of a given chemical element, and in the case when the sign is the 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 moles of hydrogen atoms,
H 2– one molecule of hydrogen, 1 mole of hydrogen.

The chemical formulas of many substances have been determined experimentally, 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 substance	1 molecule calcium carbonate
One mole of substance	6.02 10 23 molecules CaCO3
Relative molecular mass of the substance (Mr)	Мr (CaCO3) = Ar (Ca) +Ar (C) +3Ar (O) =100
Molar mass of the substance (M)	M (CaCO3) = 100 g/mol
Absolute molecular mass of the substance (m)	M (CaCO3) = Mr (CaCO3) 1.66 10 -24 g = 1.66 10 -22 g
Qualitative composition (what chemical elements form the substance)	calcium, carbon, oxygen
Quantitative composition of the substance:
*The number of atoms of each element in one molecule of a substance:*	a 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 the substance:*	In 1 mole CaCO 3(6.02 · 10 23 molecules) contained 1 mole(6.02 · 10 23 atoms) calcium, 1 mole(6.02 10 23 atoms) of carbon and 3 mol(3 6.02 10 23 atoms) of the chemical element oxygen)
Mass composition of the substance:
*Mass of each element in 1 mole of substance:*	1 mole of calcium carbonate (100g) contains the following chemical elements: 40g calcium, 12g carbon, 48g oxygen.
*Mass fractions of chemical elements in the substance (composition of the substance as a percentage by weight):*	Composition of calcium carbonate by weight: W (Ca) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (1·40)/100= 0.4 (40%) W (C) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (1 12)/100 = 0.12 (12%) W (O) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (3 16)/100 = 0.48 (48%)
For a substance with an ionic structure (salt, acid, base), the formula of the substance provides information about the number of ions of each type in the molecule, their quantity and the mass of ions per 1 mole of the substance:	Molecule CaCO 3 consists of an ion Ca 2+ and ion CO 3 2- 1 mol ( 6.02 10 23 molecules) CaCO 3 contains 1 mol 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 at standard conditions (for gases only)*

Graphic formulas

To obtain more complete information about a substance, use graphic formulas , which indicate order of connection of atoms in a molecule And valence 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 compile a graphical (structural) formula of a substance, you must:

Determine the valence of all chemical elements that form the substance.
Write down the signs of all chemical elements that form the substance, each in an amount equal to the number of atoms of a given element in the molecule.
Connect the signs of chemical elements with dashes. Each dash denotes a pair that communicates between chemical elements and therefore belongs equally to both elements.
The number of lines 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 bonded to the acid-forming element through an oxygen atom.
Oxygen atoms are combined with each other only when formulating peroxides.

Examples of graphic formulas:

The formula for the basis of life - water - is well known. Its molecule consists of two hydrogen atoms and one oxygen, which is written as H2O. If there is twice as much oxygen, then a completely different substance will be obtained - H2O2. What is it and how will the resulting substance differ from its “relative” water?

H2O2 - what is this substance?

Let's look at it in more detail. H2O2 is the formula of hydrogen peroxide, Yes, the same one that is used to treat scratches, white. Hydrogen peroxide H2O2 - scientific.

For disinfection, use a three percent peroxide solution. In pure or concentrated form, it causes chemical burns to the skin. A thirty percent peroxide solution is otherwise called perhydrol; Previously, it was used in hairdressers to bleach hair. The skin burned by it also turns white.

Chemical properties of H2O2

Hydrogen peroxide is a colorless liquid with a “metallic” taste. It is a good solvent and easily dissolves in water, ether, and alcohols.

Three and six percent peroxide solutions are usually prepared by diluting a thirty percent solution. When storing concentrated H2O2, the substance decomposes with the release of oxygen, so it should not be stored in tightly sealed containers to avoid an explosion. As the peroxide concentration decreases, its stability increases. Also, to slow down the decomposition of H2O2, you can add various substances to it, for example, phosphoric or salicylic acid. To store solutions of high concentration (more than 90 percent), sodium pyrophosphate is added to peroxide, which stabilizes the state of the substance, and aluminum vessels are also used.

H2O2 can be both an oxidizing agent and a reducing agent in chemical reactions. However, more often peroxide exhibits oxidizing properties. Peroxide is considered to be an acid, but a very weak one; salts of hydrogen peroxide are called peroxides.

as a method of producing oxygen

The decomposition reaction of H2O2 occurs when the substance is exposed to high temperature (more than 150 degrees Celsius). As a result, water and oxygen are formed.

Reaction formula - 2 H2O2 + t -> 2 H2O + O2

The oxidation state of H in H 2 O 2 and H 2 O = +1.
Oxidation state of O: in H 2 O 2 = -1, in H 2 O = -2, in O 2 = 0
2 O -1 - 2e -> O2 0

O -1 + e -> O -2
2 H2O2 = 2 H2O + O2

Hydrogen peroxide can also decompose at room temperature if a catalyst (a chemical that speeds up the reaction) is used.

In laboratories, one of the methods for producing oxygen, along with the decomposition of berthollet salt or potassium permanganate, is the decomposition reaction of peroxide. In this case, manganese (IV) oxide is used as a catalyst. Other substances that accelerate the decomposition of H2O2 are copper, platinum, and sodium hydroxide.

History of the discovery of peroxide

The first steps towards the discovery of peroxide were taken in 1790 by the German Alexander Humboldt, when he discovered the transformation of barium oxide into peroxide when heated. That process was accompanied by the absorption of oxygen from the air. Twelve years later, scientists Tenard and Gay-Lussac conducted an experiment on burning alkali metals with excess oxygen, resulting in sodium peroxide. But hydrogen peroxide was obtained later, only in 1818, when Louis Thénard studied the effect of acids on metals; a low amount of oxygen was necessary for their stable interaction. Conducting a confirmatory experiment with barium peroxide and sulfuric acid, the scientist added water, hydrogen chloride and ice to them. After a short time, Tenar discovered small frozen drops on the walls of the container with barium peroxide. It became clear that this was H2O2. Then they gave the resulting H2O2 the name “oxidized water.” This was hydrogen peroxide - a colorless, odorless, difficult-to-evaporate liquid that dissolves other substances well. The result of the interaction of H2O2 and H2O2 is a dissociation reaction, peroxide is soluble in water.

An interesting fact is that the properties of the new substance were quickly discovered, allowing it to be used in restoration work. Tenar himself, using peroxide, restored a painting by Raphael that had darkened with time.

Hydrogen peroxide in the 20th century

After careful study of the resulting substance, it began to be produced on an industrial scale. At the beginning of the twentieth century, electrochemical technology for the production of peroxide, based on the process of electrolysis, was introduced. But the shelf life of the substance obtained by this method was short, about a couple of weeks. Pure peroxide is unstable, and for the most part it was produced in thirty percent concentration for bleaching fabrics and in three or six percent concentration for household needs.

Scientists in Nazi Germany used peroxide to create a liquid-fuel rocket engine, which was used for defense purposes in World War II. As a result of the interaction of H2O2 and methanol/hydrazine, powerful fuel was obtained, on which the aircraft reached speeds of more than 950 km/h.

Where is H2O2 used now?

in medicine - for treating wounds;
in the pulp and paper industry the bleaching properties of the substance are used;
in the textile industry, natural and synthetic fabrics, furs, and wool are bleached with peroxide;
as rocket fuel or its oxidizer;
in chemistry - to produce oxygen, as a foaming agent for the production of porous materials, as a catalyst or hydrogenating agent;
for the production of disinfectants or cleaning agents, bleaches;
for bleaching hair (this is an outdated method, since hair is severely damaged by peroxide);

Hydrogen peroxide can be successfully used to solve various household problems. But only three percent hydrogen peroxide can be used for these purposes. Here are some ways:

To clean surfaces, you need to pour peroxide into a container with a spray bottle and spray it on contaminated areas.
To disinfect objects, they need to be wiped with an undiluted H2O2 solution. This will help cleanse them of harmful microorganisms. Washing sponges can be soaked in water with peroxide (1:1 ratio).
To bleach fabrics, add a glass of peroxide when washing white items. You can also rinse white fabrics in water mixed with a glass of H2O2. This method restores whiteness, protects fabrics from yellowing and helps remove stubborn stains.
To combat mold and mildew, mix peroxide and water in a 1:2 ratio in a container with a spray bottle. Spray the resulting mixture onto contaminated surfaces and after 10 minutes clean them with a brush or sponge.
You can renew darkened grout in tiles by spraying peroxide on the desired areas. After 30 minutes, you need to thoroughly rub them with a stiff brush.
To wash dishes, add half a glass of H2O2 to a full basin of water (or a sink with a closed drain). Cups and plates washed in this solution will shine clean.
To clean your toothbrush, you need to dip it in an undiluted three percent peroxide solution. Then rinse under strong running water. This method disinfects hygiene items well.
To disinfect purchased vegetables and fruits, you should spray a solution of 1 part peroxide and 1 part water on them, then rinse them thoroughly with water (can be cold).
At your summer cottage, using H2O2 you can fight plant diseases. You need to spray them with a peroxide solution or soak the seeds shortly before planting in 4.5 liters of water mixed with 30 ml of forty percent hydrogen peroxide.
To revive aquarium fish, if they are poisoned by ammonia, suffocated when the aeration is turned off, or for another reason, you can try placing them in water with hydrogen peroxide. You need to mix three percent peroxide with water at the rate of 30 ml per 100 liters and place lifeless fish in the resulting mixture for 15-20 minutes. If they do not come to life during this time, then the remedy did not help.

Even as a result of vigorously shaking a bottle of water, a certain amount of peroxide is formed in it, since the water is saturated with oxygen during this action.

Fresh fruits and vegetables also contain H2O2 until they are cooked. When heating, cooking, frying and other processes with accompanying high temperatures, a large amount of oxygen is destroyed. This is why cooked foods are considered not so healthy, although some vitamins remain in them. Freshly squeezed juices or oxygen cocktails served in sanatoriums are useful for the same reason - due to saturation with oxygen, which gives the body new strength and cleanses it.

Danger of peroxide when ingested

After the above, it may seem that peroxide can be specifically taken orally, and this will benefit the body. But this is not true at all. In water or juices, the compound is found in minimal quantities and is closely associated with other substances. Taking “unnatural” hydrogen peroxide internally (and all peroxide purchased in a store or produced as a result of chemical experiments independently cannot be considered natural, and also has too high a concentration compared to natural) can lead to dangers to life and health consequences. To understand why, we need to turn again to chemistry.

As already mentioned, under certain conditions, hydrogen peroxide breaks down and releases oxygen, which is an active oxidizing agent. can occur when H2O2 collides with peroxidase, an intracellular enzyme. The use of peroxide for disinfection is based on its oxidizing properties. So, when a wound is treated with H2O2, the released oxygen destroys living pathogenic microorganisms that have entered it. It has the same effect on other living cells. If you treat intact skin with peroxide and then wipe the treated area with alcohol, you will feel a burning sensation, which confirms the presence of microscopic damage after peroxide. But when low concentration peroxide is used externally, there will be no noticeable harm to the body.

It’s another matter if you try to take it orally. That substance, which can damage even relatively thick skin on the outside, ends up on the mucous membranes of the digestive tract. That is, chemical mini-burns occur. Of course, the released oxidizing agent - oxygen - can also kill harmful microbes. But the same process will happen with the cells of the food tract. If burns as a result of the action of the oxidizing agent are repeated, then atrophy of the mucous membranes is possible, and this is the first step on the path to cancer. The death of intestinal cells leads to the body's inability to absorb nutrients, which explains, for example, weight loss and the disappearance of constipation in some people who practice “treatment” with peroxide.

Separately, it is necessary to say about this method of using peroxide, such as intravenous injections. Even if for some reason they were prescribed by a doctor (this can only be justified in case of blood poisoning, when there are no other suitable drugs available), then under medical supervision and with strict dosage calculations, there are still risks. But in such an extreme situation, this will be a chance for recovery. Under no circumstances should you prescribe hydrogen peroxide injections to yourself. H2O2 poses a great danger to blood cells - red blood cells and platelets, since it destroys them when it enters the bloodstream. In addition, a fatal blockage of blood vessels by the released oxygen can occur - a gas embolism.

Safety precautions for handling H2O2

Keep out of the reach of children and disabled persons. The lack of odor and distinct taste makes peroxide especially dangerous for them, since large doses can be taken. If the solution gets inside, the consequences of use can be unpredictable. You should consult a doctor immediately.
Peroxide solutions with a concentration of more than three percent cause burns if they come into contact with the skin. The burn area should be washed with plenty of water.

Do not allow the peroxide solution to get into your eyes, as this will cause swelling, redness, irritation, and sometimes pain. First aid before contacting a doctor is to wash the eyes generously with water.
Store the substance in such a way that it is clear that it is H2O2, that is, in a container with a sticker to avoid accidental use for other purposes.
Storage conditions that prolong its life are a dark, dry, cool place.
Hydrogen peroxide should not be mixed with any liquids other than clean water, including chlorinated tap water.
All of the above applies not only to H2O2, but also to all preparations containing it.

2.1. Chemical language and its parts

Humanity uses many different languages. Except natural languages(Japanese, English, Russian - more than 2.5 thousand in total), there are also artificial languages, for example, Esperanto. Among artificial languages there are languages various sciences. So, in chemistry they use their own, chemical language.
Chemical language– a system of symbols and concepts designed for a brief, succinct 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 language, then we can identify similar parts in chemical language (Table 2).

Table 2.Parts of chemical language

It is impossible to master any language immediately; this also applies to a 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 names chemical substances are an integral part of the chemical language. As you study chemistry, your knowledge of chemical language will expand and deepen.

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

2.2. Chemical element symbols

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

It is impossible to replace the name of an element with a symbol in oral speech, but 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 3.Names 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"		"boron"
Bromine	Br omum	From Greek "smelly"		"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 "acid-generating"		" O"
Silicon	Si licium	From lat. "flint"		"silicium"
Krypton	Kr ypton	From Greek "hidden"		"krypton"
Magnesium	M a g nesium	From the name Magnesia Peninsula		"magnesium"
Manganese	M a n ganum	From Greek "cleansing"		"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 ccolum	From him. "St. Nicholas Copper"		"nickel"
Mercury	H ydrar g yrum	Lat. "liquid silver"		"hydrargyrum"
Lead	P lum b um	From lat. names of an alloy of lead and tin.		"plumbum"
Sulfur	S ulfur	From Sanskrit "combustible powder"		"es"
Silver	A r g entum	From Greek " light"		"argentum"
Carbon	C arboneum	From lat. " coal"		"tse"
Phosphorus	P hosphorus	From Greek "bringer of light"		"peh"
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 designate chemical substances chemical formulas.

For molecular substances, a chemical formula can denote one molecule of this substance.
Information about a substance may vary, so there are different types of chemical formulas.
Depending on the completeness of the 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.
The index "1" is not used 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 composition of water includes 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 a 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 compiled for any individual chemical substance, and for a molecular substance, in addition, it can be compiled 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.

Non-molecular substances do not have molecular formulas.

The sequence of writing element symbols in simple and molecular formulas is determined by the rules of chemical language, which you will become familiar with as you study chemistry. The information conveyed by these formulas is not affected by the sequence of symbols.

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

In a water molecule, an oxygen atom is connected by simple (single) bonds to two hydrogen atoms, but the hydrogen atoms are not connected to each other. This is precisely what the structural formula of water clearly shows.

Another example: the sulfur molecule S8. In this molecule, 8 sulfur atoms form an eight-membered ring, 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 connection of 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 to the phosphorus atom by a double bond, and the phosphorus atom, in turn, is connected to three more oxygen atoms by single bonds. Each of these three oxygen atoms is also connected by a simple bond to one of the three hydrogen atoms present in the molecule.

Compare the following three-dimensional model of a 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 “further from us”.

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

Non-molecular substances do not contain molecules. For the convenience of chemical calculations in a non-molecular substance, the so-called formula unit.

Examples of the composition of formula units of some substances: 1) silicon dioxide (quartz sand, quartz) SiO 2 – a formula unit consists of one silicon atom and two oxygen atoms; 2) sodium chloride (table 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

Information conveyed by the formula.

The simplest

Molecular

Structural

Spatial

The atoms of which elements make up the substance.
Relationships between the numbers of atoms of these elements.
The number of atoms of each element in a molecule.
Types of chemical bonds.
The sequence of joining atoms by covalent bonds.
Multiplicity of covalent bonds.
Mutual arrangement of atoms in space.
Bond lengths and angles between bonds (if specified).

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

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

The simplest formula tells us that
1) acetic acid contains carbon, hydrogen and oxygen;
2) in this substance the number of carbon atoms relates to the number of hydrogen atoms and 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 there are 2 carbon atoms, 4 hydrogen atoms and 2 oxygen atoms.
Structural formula adds that
4, 5) in a molecule two carbon atoms are connected to each other by a simple bond; one of them, in addition, is connected to three hydrogen atoms, each with a single bond, and the other to two oxygen atoms, one with a double bond and the other with a single bond; the last oxygen atom is still connected 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) This substance contains only iron, that is, it is a simple substance.

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

1) Trimetaphosphoric acid contains hydrogen, phosphorus and oxygen.
2) N H: N P: N O = 1:1:3.
3) The 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 connections in the cycle are simple. Each phosphorus atom is, in addition, connected to two more oxygen atoms, one with a double bond and the other with a single bond. Each of the three oxygen atoms connected by simple bonds to phosphorus atoms is also connected by a simple bond to a hydrogen atom.

Phosphoric acid – H 3 PO 4(another name is orthophosphoric acid) is a transparent, colorless, crystalline substance of molecular structure that melts at 42 o C. This substance dissolves very well in water and even absorbs water vapor from the air (hygroscopic). Phosphoric acid is produced in large quantities and is used primarily in the production of phosphate fertilizers, but also 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 and is included in many medicines. This acid is quite cheap, so in some countries, such as the United States, very pure phosphoric acid, highly diluted with water, is added to refreshing drinks to replace the expensive citric acid.

Methane - CH 4. If you have a gas stove at home, then you encounter this substance every day: the natural gas that burns in the burners of your stove consists of 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 for 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 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 different types of formulas for some substances-

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