Formulas of covalent bonds. Dictionary of chemical formulas Chemical formula h2

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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. Than natural languages different from artificial
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. general rule pronunciation of symbols does not exist, 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 Theoretical 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. " The 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"		" about"
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 about. 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.

The 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 more number 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 substance, and for a molecular substance, in addition, 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 to the phosphorus atom by a double bond, and the phosphorus atom, in turn, is connected to 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 of 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, each with a single bond, and the other with two oxygen atoms, with one a double bond, and 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-

The well-known formula of the basis of life - water. 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 turn out - H2O2. What is it and how will the resulting substance differ from its “relative” of water?

H2O2 - what is this substance?

Let's dwell on it in more detail. H2O2 is the formula for hydrogen peroxide, yes, the one used to treat scratches, white. Hydrogen peroxide H2O2 - scientific.

A 3% peroxide solution is used for disinfection. In pure or concentrated form, it causes chemical burns to the skin. A thirty percent peroxide solution is otherwise called perhydrol; it was previously used in hairdressing salons to bleach hair. The skin burned by him also becomes white.

Chemical properties of H2O2

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

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

H2O2 in chemical reactions can be both an oxidizing agent and a reducing agent. More often, however, 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 obtaining oxygen

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

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

The oxidation state of H in H 2 O 2 and H 2 O \u003d +1.
The oxidation state of O: in H 2 O 2 \u003d -1, in H 2 O \u003d -2, in O 2 \u003d 0
2 O -1 - 2e -> O2 0

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

Decomposition of hydrogen peroxide can also occur when room temperature, if you use a catalyst ( Chemical substance speeding up the reaction).

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

The history of the discovery of peroxide

The first steps towards the discovery of peroxide were made 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 the combustion of alkali metals with excess oxygen, resulting in sodium peroxide. But hydrogen peroxide was obtained later, only in 1818, when Louis Tenard studied the effect of acids on metals; for their stable interaction, a low amount of oxygen was needed. 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 found small solidified drops on the walls of the container with barium peroxide. It became clear that it was H2O2. Then they gave the resulting H2O2 the name "oxidized water". This was hydrogen peroxide - a colorless, odorless, hardly evaporable liquid that dissolves other substances well. The result of the interaction of H2O2 and H2O2 is a dissociation reaction, the 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 the painting by Raphael, which had darkened with time.

Hydrogen peroxide in the 20th century

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

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

Where is H2O2 used now?

in medicine - for the treatment of wounds;
in the pulp and paper industry, the bleaching properties of the substance are used;
in the textile industry, natural and synthetic fabrics, furs, 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 the hair is severely damaged by peroxide);

Hydrogen peroxide can be successfully used to solve various household problems. But only 3% hydrogen peroxide can be used for these purposes. Here are some ways:

To clean surfaces, pour peroxide into a container with a spray bottle and spray on contaminated areas.
To disinfect objects, they must be wiped with an undiluted solution of H2O2. This will help cleanse them of harmful microorganisms. Sponges for washing can be soaked in water with peroxide (proportion 1:1).
To bleach fabrics when washing white things, add a glass of peroxide. You can also rinse white fabrics in water mixed with a glass of H2O2. This method restores whiteness, prevents fabrics from yellowing and helps remove stubborn stains.
To combat mold and mildew, mix peroxide and water in a spray bottle in a ratio of 1:2. Spray the resulting mixture onto infected surfaces and clean them with a brush or sponge after 10 minutes.
You can update the darkened grout in the tile by spraying peroxide on the desired areas. After 30 minutes, you need to carefully 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 such a solution will shine with cleanliness.
To clear toothbrush, you need to lower it into an undiluted 3% peroxide solution. Then rinse under strong running water. This method disinfects the hygiene item well.
To disinfect purchased vegetables and fruits, spray a solution of 1 part peroxide and 1 part water on them, then rinse them thoroughly with water (can be cold).
On the suburban area with the help of H2O2, plant diseases can be combated. 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.
For revitalization aquarium fish If they were poisoned by ammonia, suffocated when aeration was turned off, or for another reason, you can try placing them in water with hydrogen peroxide. It is necessary to mix 3% peroxide with water at the rate of 30 ml per 100 liters and place it in the resulting mixture of lifeless fish 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 vigorous shaking of 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, boiling, roasting and other processes with concomitant high temperature destroyed a large number of oxygen. That is why cooked foods are considered not so useful, although some amount of vitamins remains in them. Freshly squeezed juices or oxygen cocktails served in sanatoriums are useful for the same reason - due to oxygen saturation, which gives the body new strength and cleanses it.

The dangers of peroxide when ingested

After the above, it may seem that peroxide can be specifically taken orally, and this will benefit the body. But that's not the case at all. In water or juices, the compound is found in minimal amounts and is closely related to other substances. Taking “unnatural” hydrogen peroxide inside (and all peroxide bought in a store or produced independently as a result of chemical experiments cannot be considered natural in any way, moreover, it has a too high concentration compared to natural) can lead to life-threatening and health-threatening consequences. To understand why, you need to turn to chemistry again.

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 the living pathogenic microorganisms that have entered it. It has the same effect on other living cells. If you treat undamaged 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 with the external use of peroxide at a low concentration, there will be no noticeable harm to the body.

Another thing, if you try to take it inside. That substance, which is capable of damaging even relatively thick skin from the outside, enters 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 occur with the cells of the alimentary tract. If burns as a result of the action of an oxidizing agent are repeated, then atrophy of the mucous membranes is possible, and this is the first step towards cancer. The death of intestinal cells leads to the inability of the body to absorb nutrients, this explains, for example, weight loss and the disappearance of constipation in some people who practice the "treatment" with peroxide.

Separately, it must be said about such a method of using peroxide 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 a strict calculation of dosages, there are still risks. But in such an extreme situation, it will be a chance for recovery. In no case should you prescribe yourself injections of hydrogen peroxide. H2O2 poses a great danger to blood cells - erythrocytes and platelets, as it destroys them when it enters the bloodstream. In addition, a deadly blockage of blood vessels by released oxygen can occur - a gas embolism.

Safety measures in handling H2O2

Keep out of the reach of children and incapacitated persons. The lack of smell and pronounced taste makes peroxide especially dangerous for them, as large doses can be taken. If the solution is ingested, the consequences of use can be unpredictable. You must immediately consult a doctor.
Peroxide solutions with a concentration of more than three percent cause burns if it comes into contact with the skin. The burn area should be washed with plenty of water.

Do not allow the peroxide solution to get into the eyes, as their swelling, redness, irritation, and sometimes pain are formed. First aid before going to the doctor - plentiful rinsing of the eyes 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 misuse.
Storage conditions that extend its life are a dark, dry, cool place.
Do not mix hydrogen peroxide with any liquids other than pure water, including chlorinated tap water.
All of the above applies not only to H2O2, but to all preparations containing it.

DEFINITION

Hydrogen(chemical symbol - H) - a chemical element with serial number 1 (the first element in the periodic system). It is located in the first period in the first (I) or seventh (VII) group of the periodic system.

Atomic mass: 1.008 amu

Electronic formula: 1s 1

The dual position of hydrogen in the periodic system is explained by the fact that it has a certain similarity with both alkali metals and halogens. Like alkali metal atoms, a hydrogen atom can donate its single electron (oxidize) and turn into a positively charged one and it is H +. Like halogen atoms, a hydrogen atom can add one more electron to obtain a stable configuration of a noble gas (helium), i.e. recover and turn into a negatively charged ion H - .

The electronegativity of hydrogen has an intermediate value (2.1) between the electronegativity values of typical metals and typical non-metals.

Hydrogen- a simple substance consisting of two hydrogen atoms.

Formula: H 2 .

Structural formula:

Under normal conditions, hydrogen is a colorless, tasteless and odorless gas. The lightest substance known. hydrogen is 0.08987 g/l under normal conditions.

In nature, hydrogen exists in the form of three isotopes with individual names: 1 H - protium (H), 2 H - deuterium (D), 3 H - tritium (T). Protium and deuterium are stable isotopes, tritium is radioactive with a half-life of 12.32 years.

Natural hydrogen consists of H 2 and HD molecules in a ratio of 3200:1. The content of pure D 2 is even less.

The physical and chemical properties of hydrogen isotopes are quite different from each other, in contrast to the isotopes of other chemical elements. This is because the addition of each additional proton causes a strong relative increase in the atom.

Hydrogen is the main component of stars and interstellar gas. The proportion of hydrogen atoms in the universe is 88.6%.

According to the reaction equation

In our case, therefore, aluminum is taken in excess, we make the calculation for hydrochloric acid.