1. Basic concepts, definitions and laws of chemistry

1.2. Atom. Chemical element. Simple substance

Atom is a central concept in chemistry. All substances are made up of atoms. Atom - the limit of fragmentation of a substance by chemical methods, i.e. an atom is the smallest chemically indivisible particle of a substance. Atomic fission is possible only in physical processes - nuclear reactions and radioactive transformations.

The modern definition of an atom: an atom is the smallest chemically indivisible electrically neutral particle, consisting of a positively charged nucleus and negatively charged electrons.

In nature, atoms exist both in a free (individual, isolated) form (for example, noble gases are composed of individual atoms), and in the composition of various simple and complex substances. It is clear that in the composition of complex substances atoms are not electrically neutral, but have an excess positive or negative charge (for example, Na + Cl -, Ca 2+ O 2–), i.e. in complex substances, atoms can be in the form of monatomic ions. Atoms and the monatomic ions formed from them are called atomic particles.

The total number of atoms in nature cannot be counted, but they can be classified into narrower types, just like, for example, all trees in a forest are divided into birches, oaks, spruces, pines, etc. The nucleus charge is taken as the basis for the classification of atoms according to certain types, i.e. the number of protons in the nucleus of an atom, since it is this characteristic that is preserved, regardless of whether the atom is in a free or chemically bound form.

Chemical element is a kind of atomic particles with the same nuclear charge.

For example, the chemical element sodium is meant, regardless of whether free sodium atoms or Na + ions are considered in the composition of salts.

You should not confuse the concepts of an atom, chemical element and simple substance... An atom is a concrete concept, atoms really exist, and a chemical element is an abstract, collective concept. For example, in nature there are specific copper atoms with rounded relative atomic masses 63 and 65. But the chemical element copper is characterized by the average relative atomic mass given in the periodic table of chemical elements of D.I. Mendeleev, which, taking into account the content of isotopes, is equal to 63.54 (in nature, copper atoms with such a value of A r are absent). An atom in chemistry is traditionally understood as an electrically neutral particle, while a chemical element in nature can be represented by both electrically neutral and charged particles - monatomic ions:,,,.

A simple substance is one of the forms of existence of a chemical element in nature (another form is a chemical element in the composition of complex substances). For example, the chemical element oxygen in nature exists in the form of a simple substance O 2 and as part of a number of complex substances (H 2 O, Na 2 SO 4 ⋅ 10H 2 O, Fe 3 O 4). Often, the same chemical element forms several simple substances. In this case, they speak of allotropy - the phenomenon of the existence of an element in nature in the form of several simple substances. The simplest substances themselves are called allotropic modifications ( modifications). A number of allotropic modifications are known for carbon (diamond, graphite, carbyne, fullerene, graphene, tubulenes), phosphorus (white, red and black phosphorus), oxygen (oxygen and ozone). Due to the phenomenon of allotropy of simple substances, about 5 times more are known than chemical elements.

Allotropy reasons:

• differences in the quantitative composition of molecules (O 2 and O 3);
• differences in the structure of the crystal lattice (diamond and graphite).

Allotropic modifications of a given element always differ in physical properties and chemical activity. For example, ozone is more active than oxygen, and the melting point of diamond is higher than that of fullerene. Allotropic modifications under certain conditions (changes in pressure, temperature) can transform into each other.

In most cases, the names of a chemical element and a simple substance coincide (copper, oxygen, iron, nitrogen, etc.), therefore it is necessary to distinguish between the properties (characteristics) of a simple substance as a set of particles and the properties of a chemical element as a type of atoms with the same nuclear charge.

A simple substance is characterized by structure (molecular or non-molecular), density, a certain state of aggregation under given conditions, color and odor, electrical and thermal conductivity, solubility, hardness, boiling and melting points (boiling point and melting point), viscosity, optical and magnetic properties , molar (relative molecular) weight, chemical formula, chemical properties, methods of production and use. We can say that the properties of a substance are the properties of a set of chemically bound particles, i.e. physical body, since one atom or molecule has no taste, smell, solubility, melting and boiling points, color, electrical and thermal conductivity.

Properties (characteristics) chemical element: atomic number, chemical sign, relative atomic mass, atomic mass, isotopic composition, abundance in nature, position in the periodic system, atomic structure, ionization energy, electron affinity, electronegativity, oxidation states, valence, allotropy phenomenon, mass and mole fraction in the composition of a complex substance, absorption and emission spectra. We can say that the properties of a chemical element are the properties of a single particle or isolated particles.

The differences between the concepts of "chemical element" and "simple substance" are shown in table. 1.2 using nitrogen as an example.

Table 1.2

Differences between the concepts of "chemical element" and "simple substance" for nitrogen

Nitrogen is a chemical element	Nitrogen is a simple substance
1. Atomic number 7.	1. Gas (n.o.) colorless, odorless and tasteless, non-toxic.
2. Chemical sign N.	2. Nitrogen has a molecular structure, formula N 2, the molecule consists of two atoms.
3. Relative atomic mass 14.	3. Molar mass 28 g / mol.
4. In nature, it is represented by nuclides 14 N and 15 N.	4. Poorly soluble in water.
5. Mass fraction in the earth's crust 0.030% (16th place in prevalence).	5. Density (n.u.) 1.25 g / dm 3, slightly lighter than air, relative density for helium 7.
6. Has no allotropic modifications.	6. Dielectric, poorly conducts heat.
7. It is a part of various salts - nitrates (KNO 3, NaNO 3, Ca (NO 3) 2).	7. t bale \u003d −195.8 ° C; t pl \u003d −210.0 ° C.
8. Mass fraction in ammonia 82.35%, is a part of proteins, amines, DNA.	8. Dielectric constant 1.00.
9. The mass of an atom is (for 14 N) 14u or 2.324 · 10 −23 g.	9. The dipole moment is 0.
10. Atomic structure: 7p, 7e, 7n (for 14 N), electronic configuration 1s 2 2s 2 2p 3, two electron layers, five valence electrons, etc.	10. Has a molecular crystal lattice (in solid state).
11. In the periodic table, it is in the 2nd period and VA-group, belongs to the family of p -elements.	11. In the atmosphere, the volume fraction is 78%.
12. Ionization energy 1402.3 kJ / mol, electron affinity -20 kJ / mol, electronegativity 3.07.	12. World production 44 · 10 6 tons per year.
13. Shows covalences I, II, III, IV and oxidation states –3, –2, –1, 0, +1, +2, +3, +4, +5.	13. Get: in the laboratory - heating NH 4 NO 2; in industry - by heating liquefied air.
14. The radius of the atom (orbital) 0.052 nm.	14. Chemically inactive, when heated it interacts with oxygen, metals.
15. Main line in the spectrum of 399.5 nm.	15. It is used to create an inert atmosphere when drying explosives, when storing valuable paintings and manuscripts, to create low temperatures (liquid nitrogen).
16. The body of an average person (body weight 70.0 kg) contains 1.8 kg of nitrogen.
17. As part of ammonia, it participates in the formation of hydrogen bonds.

Example 1.2. Indicate in which of the following statements oxygen is referred to as a chemical element:

• a) the mass of the atom is 16u;
• b) forms two allotropic modifications;
• c) the molar mass is 32 g / mol;
• d) poorly soluble in water.

Decision. Statements c), d) refer to a simple substance, and statements a), b) - to the chemical element oxygen.

Answer: 3).

Each chemical element has its own conventional designation - chemical sign (symbol): K, Na, O, N, Cu, etc.

A chemical sign can also express the composition of a simple substance. For example, the symbol for the chemical element Fe also reflects the composition of the simple substance iron. However, the chemical signs O, H, N, Cl denote only chemical elements; simple substances have the formulas O 2, H 2, N 2, Cl 2.

As already noted, in most cases the names of chemical elements and simple substances coincide. Exceptions are the names of allotropic modifications of carbon (diamond, graphite, carbyne, fullerene) and one of the modifications of oxygen (oxygen and ozone). For example, when we use the word "graphite", we mean only a simple substance (but not a chemical element) carbon.

The prevalence of chemical elements in nature is expressed in mass and mole fractions. Mass fraction w is the ratio of the mass of atoms of a given element to the total mass of atoms of all elements. Mole fraction χ is the ratio of the number of atoms of a given element to the total number of atoms of all elements.

In the earth's crust (a layer about 16 km thick), oxygen atoms have the largest mass (49.13%) and molar (55%) fractions, followed by silicon atoms (w (Si) \u003d 26%, χ (Si) \u003d 16 , 35%). In the Galaxy, almost 92% of the total number of atoms are hydrogen atoms, and 7.9% are helium atoms. Mass fractions of atoms of the main elements in the human body: O - 65%, C - 18%, H - 10%, N - 3%, Ca - 1.5%, P - 1.2%.

The absolute values \u200b\u200bof the atomic masses are extremely small (for example, the mass of an oxygen atom is about 2.7 ⋅ 10 −23 g) and inconvenient for calculations. For this reason, a scale for the relative atomic masses of elements was developed. At present, 1/12 of the mass of the atom of the C-12 nuclide is taken as the unit of measurement of relative atomic masses. This quantity is called constant atomic mass or atomic mass unit (a.m.) and has the international designation u:

m u \u003d 1 a. i.e. m \u003d 1 u \u003d 1/12 (m a 12 C) \u003d

1.66 ⋅ 10 - 24 g \u003d 1.66 ⋅ 10 - 27 kg.

It is easy to show that the numerical value of u is equal to 1 / N A:

1 u \u003d 1 12 m a (12 C) \u003d 1 12 M (C) N A \u003d 1 12 12 N A \u003d 1 N A \u003d

1 6.02 ⋅ 10 23 \u003d 1.66 ⋅ 10 - 24 (d).

Relative atomic mass of an elementAr (E) is a physical dimensionless quantity that shows how many times the mass of an atom or the average mass of an atom (respectively, for isotopically pure and isotopically mixed elements) is more than 1/12 of the mass of an atom of the nuclide C-12:

A r (E) \u003d m a (E) 1 a. f.s. \u003d m a (E) 1 u. (1.1)

Knowing the relative atomic mass, you can easily calculate the mass of an atom:

m a (E) \u003d A r (E) u \u003d A r (E) ⋅ 1.66 ⋅ 10 −24 (g) \u003d

A r (E) ⋅ 1.66 ⋅ 10 −27 (kg).

Molecule. And he. Substances of molecular and non-molecular structure. Chemical equation

When atoms interact, more complex particles are formed - molecules.

Molecule is the smallest electrically neutral isolated set of atoms capable of independent existence and is the carrier of the chemical properties of a substance.

The molecules have the same qualitative and quantitative composition as the substance they form. The chemical bond between atoms in a molecule is much stronger than the forces of interaction between molecules (which is why a molecule can be considered as a separate, isolated particle). In chemical reactions, molecules, unlike atoms, are not preserved (destroyed). Like an atom, an individual molecule does not possess such physical properties of a substance as color and odor, melting and boiling points, solubility, heat and electrical conductivity, etc.

We emphasize that a molecule is precisely the carrier of the chemical properties of a substance; it cannot be said that a molecule retains (has exactly the same) chemical properties of a substance, since the chemical properties of a substance are significantly influenced by intermolecular interaction, which is absent for an individual molecule. For example, the substance trinitroglycerin has the ability to explode, but not a separate molecule of trinitroglycerin.

Ion - an atom or group of atoms with a positive or negative charge.

Positively charged ions are called cations, and negatively charged ions are called anions. Ions are simple, i.e. monoatomic (K +, Cl -) and complex (NH 4 +, NO 3 -), one - (Na +, Cl -) and multiply charged (Fe 3+, PO 4 3 -).

1. For a given element, a simple ion and a neutral atom have the same number of protons and neutrons, but differ in the number of electrons: the cation has fewer, and the anion has more than the electrically neutral atom.

2. The mass of a simple or complex ion is the same as the mass of the corresponding electrically neutral particle.

It should be borne in mind that not all substances are composed of molecules.

Substances consisting of molecules are called substances of molecular structure... It can be both simple (argon, oxygen, fullerene) and complex (water, methane, ammonia, benzene) substances.

All gases and practically all liquids have a molecular structure (with the exception of mercury); Solids can have both molecular (sucrose, fructose, iodine, white phosphorus, phosphoric acid) and non-molecular structure (diamond, black and red phosphorus, SiC carborundum, sodium chloride). In substances of molecular structure, the bonds between molecules (intermolecular interaction) are weak. They are easily destroyed when heated. It is for this reason that substances of molecular structure have relatively low melting and boiling points, are volatile (as a result, they often have an odor).

Substances of non-molecular structure consist of electrically neutral atoms or simple or complex ions. Electrically neutral atoms consist, for example, of diamond, graphite, black phosphorus, silicon, boron, and of simple and complex ions - salts, such as KF and NH 4 NO 3. Metals are composed of positively charged atoms (cations). Carborundum SiC, silicon oxide (IV) SiO 2, alkalis (KOH, NaOH), most salts (KCl, CaCO 3), binary metal compounds with non-metals (basic and amphoteric oxides, hydrides, carbides, silicides, nitrides, phosphides), intermetallic compounds (compounds of metals with each other). In substances of non-molecular structure, individual atoms or ions are linked by strong chemical bonds, therefore, under normal conditions, these substances are solid, non-volatile, and have high melting points.

For example, sucrose (molecular structure) melts at 185 ° C, and sodium chloride (non-molecular structure) melts at 801 ° C.

In the gas phase, all substances are composed of molecules, and even those that have a non-molecular structure at ordinary temperatures. For example, at high temperatures in the gas phase, molecules of NaCl, K 2, SiO 2 are found.

For substances that decompose upon heating (CaCO 3, KNO 3, NaHCO 3), molecules cannot be obtained by heating the substance

Molecular substances form the basis of the organic world, and non-molecular substances form the basis of the inorganic (mineral) world.

Chemical formula. Formula unit. Chemical equation

The composition of any substance is expressed using a chemical formula. Chemical formula - this is an image of the qualitative and quantitative composition of a substance using symbols of chemical elements, as well as numerical, alphabetic and other signs.

For simple substances of non-molecular structure, the chemical formula coincides with the sign of the chemical element (for example, Cu, Al, B, P). In the formula of a simple substance of molecular structure, indicate (if necessary) the number of atoms in a molecule: O 3, P 4, S 8, C 60, C 70, C 80, etc. Formulas of noble gases are always written with one atom: He, Ne, Ar, Xe, Kr, Rn. When writing down the equations of chemical reactions, the chemical formulas of some polyatomic molecules of simple substances can (unless otherwise specified) be written in the form of symbols of elements (single atoms): P 4 → P, S 8 → S, C 60 → C (this cannot be done for ozone O 3, oxygen O 2, nitrogen N 2, halogens, hydrogen).

For complex substances of molecular structure, empirical (simplest) and molecular (true) formulas are distinguished. Empirical formula shows the smallest integer ratio of the numbers of atoms in a molecule, and molecular formula - true integer ratio of atoms. For example, the true formula for ethane is C 2 H 6, and the simplest is CH 3. The simplest formula is obtained by dividing (reducing) the number of atoms of the elements in the true formula by any suitable number. For example, the simplest formula for ethane was obtained by dividing the numbers of C and H atoms by 2.

The simplest and true formulas can both coincide (methane CH 4, ammonia NH 3, water H 2 O) or not coincide (phosphorus oxide (V) P 4 O 10, benzene C 6 H 6, hydrogen peroxide H 2 O 2, glucose C 6 H 12 O 6).

Chemical formulas allow you to calculate the mass fractions of atoms of elements in a substance.

The mass fraction w of atoms of element E in a substance is determined by the formula

w (E) \u003d A r (E) ⋅ N (E) M r (V), (1.2)

where N (E) is the number of atoms of an element in the formula of a substance; M r (B) - relative molecular (formula) mass of a substance.

For example, for sulfuric acid M r (H 2 SO 4) \u003d 98, then the mass fraction of oxygen atoms in this acid

w (O) \u003d A r (O) ⋅ N (O) M r (H 2 SO 4) \u003d 16 ⋅ 4 98 ≈ 0.653 (65.3%).

According to the formula (1.2), the number of atoms of an element in a molecule or formula unit is found:

N (E) \u003d M r (V) ⋅ w (E) A r (E) (1.3)

or molar (relative molecular or formula) mass of a substance:

M r (V) \u003d A r (E) ⋅ N (E) w (E). (1.4)

In formulas 1.2–1.4, the values \u200b\u200bof w (E) are given in fractions of a unit.

Example 1.3. In some substance, the mass fraction of sulfur atoms is 36.78%, and the number of sulfur atoms in one formula unit is two. Indicate the molar mass (g / mol) of the substance:

Decision . Using formula 1.4, we find

M r \u003d A r (S) ⋅ N (S) w (S) \u003d 32 ⋅ 2 0.3678 \u003d 174,

M \u003d 174 g / mol.

Answer: 2).

The following example shows how to find the simplest formula for a substance by mass fractions of elements.

Example 1.4. In some chlorine oxide, the mass fraction of chlorine atoms is 38.8%. Find the oxide formula.

Decision . Since w (Cl) + w (O) \u003d 100%, then

w (O) \u003d 100% - 38.8% \u003d 61.2%.

If the mass of the substance is 100 g, then m (Cl) \u003d 38.8 g and m (O) \u003d 61.2 g.

Let's represent the oxide formula as Cl x O y. We have

x: y \u003d n (Cl): n (O) \u003d m (Cl) M (Cl): m (O) M (O);

x: y \u003d 38.8 35.5: 61.2 16 \u003d 1.093: 3.825.

Dividing the obtained numbers by the smallest of them (1,093), we find that x: y \u003d 1: 3.5 or, multiplying by 2, we get x: y \u003d 2: 7. Therefore, the oxide formula is Cl 2 O 7.

Answer: Cl 2 O 7.

For all complex substances of non-molecular structure, chemical formulas are empirical and reflect the composition not of molecules, but of the so-called formula units.

Formula unit (PU) - a group of atoms corresponding to the simplest formula of a substance of non-molecular structure.

Thus, chemical formulas of substances of non-molecular structure are formula units. Examples of formula units: KOH, NaCl, CaCO 3, Fe 3 C, SiO 2, SiC, KNa 2, CuZn 3, Al 2 O 3, NaH, Ca 2 Si, Mg 3 N 2, Na 2 SO 4, K 3 PO 4, etc.

Formula units can be considered as structural units of substances of non-molecular structure. For substances of molecular structure, such, obviously, are actually existing molecules.

Using chemical formulas, the equations of chemical reactions are written.

Chemical equation is a conditional notation of a chemical reaction using chemical formulas and other signs (equal, plus, minus, arrows, etc.).

The chemical equation is a consequence of the law of conservation of mass, therefore, it is composed so that the numbers of atoms of each element in its both parts are equal.

The numbers in front of the formulas are called stoichiometric coefficients, while the unit is not written, but it is implied (!) and is taken into account when calculating the total sum of stoichiometric coefficients. Stoichiometric coefficients show in what molar ratios the starting materials react and reaction products are formed. For example, for a reaction whose equation is

3Fe 3 O 4 + 8Al \u003d 9Fe + 4Al 2 O 3

n (Fe 3 O 4) n (Al) \u003d 3 8; n (Al) n (Fe) \u003d 8 9, etc.

In reaction schemes, the coefficients are not placed and instead of the equal sign, an arrow is used:

FeS 2 + O 2 → Fe 2 O 3 + SO 2

The arrow is also used when writing the equations of chemical reactions with the participation of organic substances (so as not to confuse the equals sign with a double bond):

CH 2 \u003d CH 2 + Br 2 → CH 2 Br – CH 2 Br,

as well as equations of electrochemical dissociation of strong electrolytes:

NaCl → Na + + Cl -.

Constant composition law

For substances of molecular structure, it is true consistency law (J. Proust, 1808): any substance of molecular structure, regardless of the method and conditions of production, has a constant qualitative and quantitative composition.

From the law of constancy of composition, it follows that in molecular compounds the elements must be in strictly defined mass proportions, i.e. have a constant mass fraction. This is true if the isotopic composition of the element does not change. For example, the mass fraction of hydrogen atoms in water, regardless of the way it is obtained from natural substances (synthesis from simple substances, heating of copper sulfate CuSO 4 · 5H 2 O, etc.) will always be equal to 11.1%. However, in water obtained by the interaction of deuterium molecules (a hydrogen nuclide with A r ≈ 2) and natural oxygen (A r \u003d 16), the mass fraction of hydrogen atoms is

w (H) \u003d 2 ⋅ 2 2 ⋅ 2 + 16 \u003d 0.2 (20%).

Substances obeying the law of constancy of composition, i.e. substances of molecular structure are called stoichiometric.

Substances of non-molecular structure (especially carbides, hydrides, nitrides, oxides and sulfides of metals of the d -family) do not obey the law of constancy of composition, therefore they are called non-stoichiometric... For example, depending on the production conditions (temperature, pressure), the composition of titanium (II) oxide is variable and varies within the range of TiO 0.7 –TiO 1.3, ie. in the crystal of this oxide, there can be from 7 to 13 oxygen atoms per 10 titanium atoms. However, for many substances of non-molecular structure (KCl, NaOH, CuSO 4), deviations from the constancy of the composition are very insignificant, so we can assume that their composition is practically independent of the method of preparation.

Relative molecular and formula weight

To characterize substances of molecular and non-molecular structure, respectively, the concepts "relative molecular weight" and "relative formula weight" are introduced, which are denoted by the same symbol - M r

Relative molecular weight is a dimensionless physical quantity that shows how many times the mass of a molecule is greater than 1/12 of the mass of an atom of the C-12 nuclide:

M r (B) \u003d m mol (B) u. (1.5)

Relative formula mass is a dimensionless physical quantity that shows how many times the mass of a formula unit is greater than 1/12 of the mass of an atom of the C-12 nuclide:

M r (B) \u003d m ФЕ (B) u. (1.6)

Formulas (1.5) and (1.6) allow us to find the mass of a molecule or PU:

m (mol, FE) \u003d uM r. (1.7)

In practice, the values \u200b\u200bof M r are found by summing the relative atomic masses of the elements forming a molecule or formula unit, taking into account the number of individual atoms. For example:

M r (H 3 PO 4) \u003d 3A r (H) + A r (P) + 4A r (O) \u003d

3 ⋅ 1 + 31 + 4 ⋅ 16 = 98.

Water is one of the most abundant substances in nature (the hydrosphere occupies 71% of the Earth's surface). Water plays an important role in geology and the history of the planet. The existence of living organisms is impossible without water. The fact is that the human body is almost 63% - 68% water. Almost all biochemical reactions in every living cell are reactions in aqueous solutions ... In solutions (mostly aqueous), most of the technological processes take place in the chemical industry, in the production of medicines and food products. And in metallurgy, water is extremely important, and not only for cooling. It is no coincidence that hydrometallurgy - the extraction of metals from ores and concentrates using solutions of various reagents - has become an important industry.

Water, you have no color, no taste, no smell
you cannot be described, you are enjoyed
not knowing what you are. It cannot be said
what is necessary for life: you are life itself.
You fulfill us with joy
which cannot be explained by our feelings.
With you forces return to us,
with whom we have already said goodbye.
By your grace they begin again in us
seethe dried springs of our heart.
(A. de Saint-Exupery. Planet of the people)

I have written an essay on the topic "Water is the most amazing substance in the world." I chose this topic because it is the most relevant topic, since water is the most important substance on Earth without which no living organism can exist and no biological, chemical reactions, and technological processes can occur.

Water is the most amazing substance on Earth

Water is a familiar and unusual substance. The famous Soviet scientist Academician IV Petryanov called his popular science book on water "the most extraordinary substance in the world." And "Entertaining Physiology", written by BF Sergeev, Doctor of Biological Sciences, begins with a chapter on water - "The substance that created our planet."
Scientists are absolutely right: there is no substance on Earth that is more important for us than ordinary water, and at the same time there is no such substance in the properties of which there would be as many contradictions and anomalies as in its properties.

Almost 3/4 of the surface of our planet is occupied by oceans and seas. Solid water - snow and ice - covers 20% of the land. The planet's climate depends on water. Geophysicists argue that the Earth would have cooled down long ago and turned into a lifeless piece of stone, if not for water. It has a very high heat capacity. When heated, it absorbs heat; cooling down, gives it away. Earth's water both absorbs and returns a lot of heat and thus "evens out" the climate. And the Earth is protected from the cosmic cold by those water molecules that are scattered in the atmosphere - in clouds and in the form of vapors ... you cannot do without water - this is the most important substance on Earth.
Water molecule structure

The behavior of the water is "illogical". It turns out that the transitions of water from a solid state to a liquid and gaseous occurs at temperatures much higher than it should be. An explanation has been found for these anomalies. The H2O water molecule is built in the form of a triangle: the angle between the two oxygen-hydrogen bonds is 104 degrees. But since both hydrogen atoms are located on the same side of oxygen, electrical charges are dispersed in it. The water molecule is polar, which is the reason for the special interaction between its different molecules. The hydrogen atoms in the H 2 O molecule, having a partial positive charge, interact with the electrons of the oxygen atoms of the neighboring molecules. This chemical bond is called hydrogen. It unites H 2 O molecules into peculiar spatial polymers; the plane in which the hydrogen bonds are located are perpendicular to the plane of the atoms of the same H2O molecule. The interaction between water molecules explains, first of all, the irregularly high temperatures of its melting and boiling. Additional energy must be supplied to loosen and then break the hydrogen bonds. And this energy is very significant. That is why, by the way, the heat capacity of water is so high.

What connections does H 2 O have?

In a water molecule, there are two polar covalent bonds H-O.

They are formed due to the overlap of two one-electron p-clouds of an oxygen atom and one-electron S-clouds of two hydrogen atoms.

In a water molecule, the oxygen atom has four electron pairs. Two of them are involved in the formation of covalent bonds, i.e. are binding. The other two electron pairs are non-bonding.

There are four poles of charges in a molecule: two are positive and two are negative. Positive charges are concentrated at hydrogen atoms, since oxygen is electronegative than hydrogen. The two negative poles are on the two non-bonding electron pairs of oxygen.

This idea of \u200b\u200bthe structure of the molecule allows us to explain many properties of water, in particular the structure of ice. In the crystal lattice of ice, each of the molecules is surrounded by four others. In a plane image, this can be represented as follows:

The diagram shows that the connection between the molecules is carried out through the hydrogen atom:
A positively charged hydrogen atom of one water molecule is attracted to a negatively charged oxygen atom of another water molecule. This bond is called hydrogen (it is designated by dots). The strength of a hydrogen bond is about 15 - 20 times weaker than a covalent bond. Therefore, the hydrogen bond is easily broken, which is observed, for example, during the evaporation of water.

The structure of liquid water resembles that of ice. In liquid water, molecules are also linked to each other through hydrogen bonds, but the structure of water is less "rigid" than that of ice. Due to the thermal motion of molecules in water, some hydrogen bonds are broken, others are formed.

Physical properties of H 2 O

Water, H2O, odorless liquid, tasteless, colorless (bluish in thick layers); density 1 g / cm 3 (at 3.98 degrees), t pl \u003d 0 degrees, t bale \u003d 100 degrees.
There are different kinds of water: liquid, solid and gaseous.
Water is the only substance in nature that under terrestrial conditions exists in all three states of aggregation:

liquid - water
hard - ice
gaseous - steam

The Soviet scientist V. I. Vernadsky wrote: “Water stands alone in the history of our planet. There is no natural body that could compare with it in terms of its influence on the course of the main, most grandiose geological processes. There is no earthly substance - a mineral of a rock, a living body, which would not contain it. All earthly matter is permeated and enveloped by it. "

Chemical properties of H 2 O

Of the chemical properties of water, the ability of its molecules to dissociate (decompose) into ions and the ability of water to dissolve substances of different chemical nature are especially important. The role of water as the main and universal solvent is primarily determined by the polarity of its molecules (displacement of the centers of positive and negative charges) and, as a consequence, its extremely high dielectric constant. Opposite electric charges, and in particular ions, are attracted to each other in water 80 times weaker than they would in air. The forces of mutual attraction between molecules or atoms of a body submerged in water are also weaker than in air. In this case, it is easier for heat movement to separate the molecules. That is why dissolution occurs, including many hardly soluble substances: a drop wears away a stone ...

Dissociation (decomposition) of water molecules into ions:
H 2 O → H + + OH, or 2H 2 O → H 3 O (hydroxy ion) + OH
under normal conditions it is extremely insignificant; on average, one molecule out of 500,000,000 dissociates. It should be borne in mind that the first of the above equations is purely conditional: a proton H, devoid of an electron shell, cannot exist in an aqueous medium. It immediately combines with a water molecule, forming a hydroxium ion H 3 O. even that the associates of water molecules actually decay into much heavier ions, such as, for example,
8H 2 O → HgO 4 + H 7 O 4, and the reaction H 2 O → H + + OH - is just a very simplified scheme of the real process.

The reactivity of water is relatively low. True, some active metals are able to displace hydrogen from it:
2Na + 2H 2 O → 2NaOH + H 2,

and in an atmosphere of free fluorine, water can burn:
2F 2 + 2H 2 O → 4HF + O 2.

Crystals of ordinary ice also consist of similar molecular associates of molecular compounds. The "packing" of atoms in such a crystal is not ionic, and ice does not conduct heat well. The density of liquid water at a temperature close to zero is greater than that of ice. At 0 ° C, 1 gram of ice occupies a volume of 1.0905 cm 3, and 1 gram of liquid water - 1,0001 cm 3. And the ice floats, which is why the reservoirs do not freeze through and through, but only become covered with ice. This is another anomaly of water: after melting, it first contracts, and only then, at the turn of 4 degrees, with the further process it begins to expand. At high pressures, ordinary ice can be turned into the so-called ice - 1, ice - 2, ice - 3, etc. - heavier and denser crystalline forms of this substance. The hardest, densest and most refractory while ice - 7 - obtained at a pressure of 3 kilo Pa. It melts at 190 degrees.

The water cycle in nature

The human body is permeated with millions of blood vessels. Large arteries and veins connect the main organs of the body with each other, smaller ones braid them from all sides, the thinnest capillaries reach almost every single cell. Whether you are digging a hole, sitting in a lesson or blissfully sleeping, blood flows continuously through them, linking the brain and stomach, kidneys and liver, eyes and muscles into a single system of the human body. What is blood for?

Blood carries oxygen from the lungs and nutrients from the stomach to every cell in your body. Blood collects waste from all, even the most secluded corners of the body, freeing it from carbon dioxide and other unnecessary, including hazardous substances. The blood carries special substances throughout the body - hormones that regulate and coordinate the work of various organs. In other words, blood connects different parts of the body into a single system, into a well-coordinated and efficient organism.

Our planet also has a circulatory system. The blood of the Earth is water, and the blood vessels are rivers, streams, streams and lakes. And this is not just a comparison, an artistic metaphor. Water on Earth plays the same role as blood in the human body, and as scientists recently noticed, the structure of the river network is very similar to the structure of the human circulatory system. "The driver of nature" - this is how the great Leonardo da Vinci called water, passing from soil to plants, from plants to atmosphere, flowing down rivers from continents to oceans and returning back with air currents, connecting various components of nature with each other, transforming them into a single geographic system. Water does not just pass from one natural component to another. Like blood, it carries with it a huge amount of chemicals, exporting them from soil to plants, from land to lakes and oceans, from the atmosphere to earth. All plants can consume soil nutrients only with water, where they are in a dissolved state. If it were not for the flow of water from the soil into the plants, all herbs, even those growing on the richest soils, would have perished "of hunger", becoming like a merchant who died of hunger on a chest of gold. Water supplies nutrients to the inhabitants of rivers, lakes and seas. The streams, merrily flowing from fields and meadows during the spring melting of snow or after summer rains, collect chemicals stored in the soil along the way and bring them to the inhabitants of reservoirs and the sea, thereby linking the land and water parts of our planet. The richest "table" is formed in those places where rivers carrying nutrients flow into lakes and seas. Therefore, such areas of the coast - estuaries - are distinguished by a riot of underwater life. And who removes waste from different geographic systems? Again, water, and as an accelerator, it works much better than the human circulatory system, which only partially fulfills this function. The purifying role of water is especially important now, when a person poisons the environment with waste from cities, industrial and agricultural enterprises. The body of an adult contains about 5-6 kg. blood, most of which is constantly circulating between different parts of his body. And how much water does the life of our world serve?

All waters on earth that are not part of rocks are united by the concept of "hydrosphere". Its weight is so great that it is usually measured not in kilograms or tons, but in cubic kilometers. One cubic kilometer is a cube with each edge 1 km in size, constantly occupied by water. The weight of 1 km 3 of water is equal to 1 billion tons. The entire earth contains 1.5 billion km 3 of water, which by weight is approximately 15,000,000,000,000,000,000 tons! Each person has 1.4 km 3 of water, or 250 million tons. Drink, I don’t want to!
Unfortunately, it's not that simple. The fact is that 94% of this volume is made up of the waters of the world ocean, which are not suitable for most economic purposes. Only 6% is land water, of which only 1/3 is fresh, i.e. only 2% of the total volume of the hydrosphere. The bulk of this fresh water is concentrated in glaciers. Much less of them are contained under the earth's surface (in shallow underground, water horizons, in underground lakes, in soils, as well as in atmospheric vapors. The share of rivers, from which people mainly take water, account for very few - 1.2 thousand km 3. The total volume of water contained in living organisms at a time is absolutely insignificant. So there is not so much water on our planet that can be consumed by humans and other living organisms. But why does it not end? After all, people and animals they constantly drink water, plants evaporate it into the atmosphere, and rivers carry it into the ocean.

Why doesn't water end on Earth?

The human circulatory system is a closed circuit through which blood flows continuously, carrying oxygen and carbon dioxide, nutrients and waste products. This stream never ends, because it is a circle or a ring, and, as you know, "the ring has no end." The water network of our planet is arranged according to the same principle. Water on Earth is in a constant cycle, and its loss in one link is immediately replenished due to the flow from the other. The driving force behind the water cycle is solar energy and gravity. Due to the water cycle, all parts of the hydrosphere are closely united and connect other components of nature with each other. In its most general form, the water cycle on our planet looks like this. Under the influence of sunlight, water evaporates from the surface of the ocean and land and enters the atmosphere, and evaporation from the surface of the land is carried out both by rivers and reservoirs, as well as by soil and plants. Part of the water immediately returns with rains back to the ocean, and part is carried by winds to land, where it falls in the form of rains and snow. Once in the soil, water is partially absorbed into it, replenishing the reserves of soil moisture and groundwater, partially flowing over the surface into rivers and reservoirs, soil moisture partially passes into plants, which evaporate it into the atmosphere, and partially flows into rivers, only at a lower speed. Rivers fed by water from surface streams and underground waters carry water to the World Ocean, replenishing its loss. Water evaporates from its surface, returns to the atmosphere, and the cycle closes. The same movement of water between all the components of nature and all parts of the earth's surface occurs continuously and continuously for many millions of years.

I must say that the water cycle is not completely closed. Part of it, getting into the upper layers of the atmosphere, decomposes under the influence of sunlight and goes into space. But these insignificant losses are constantly replenished by the influx of water from the deep layers of the earth during volcanic eruptions. Due to this, the volume of the hydrosphere is gradually increasing. according to some calculations, 4 billion years ago, its volume was 20 million km 3, i.e. was seven thousand times smaller than modern. In the future, the amount of water on Earth, apparently, will also increase, if we take into account that the volume of water in the Earth's mantle is estimated at 20 billion km 3 - this is 15 times more than the current volume of the hydrosphere. By comparing the volume of water in individual parts of the hydrosphere with the inflow of water into them and neighboring links of the cycle, it is possible to determine the activity of water exchange, i.e. the time during which the volume of water in the World Ocean, in the atmosphere or soil can be completely renewed. The slowest renewal of water is in polar glaciers (once every 8 thousand years). And river water is renewed the fastest, which completely changes in all rivers on Earth in 11 days.

Planet water hunger

"The Earth is a planet of amazing blue!" - the American astronauts returning from distant Space after landing on the moon enthusiastically reported. And could our planet look different if more than 2/3 of its surface is occupied by seas and oceans, glaciers and lakes, rivers, ponds and reservoirs. But then, what does the phenomenon, the name of which is given in the headlines, mean? What kind of "hunger" can there be if there is such an abundance of reservoirs on Earth? Yes, there is more than enough water on Earth. But we must not forget that life on planet Earth, according to scientists, first appeared in water, and only then came to land. Organisms have retained their dependence on water during evolution for many millions of years. Water is the main "building material" of which their body is composed. This is easy to verify by analyzing the figures in the following tables:

The last number in this table indicates that a person weighing 70 kg. contains 50 kg. water! But even more of it is in the human embryo: in a three-day - 97%, in a three-month - 91%, in an eight-month - 81%.

The problem of "water hunger" is the need for incontinence of a certain amount of water in the body, as there is a constant loss of moisture in the course of various physiological processes. For a normal existence in a temperate climate, a person needs to receive about 3.5 liters of water per day with food and drink, in the desert this rate increases to at least 7.5 liters. Without food, a person can exist for about forty days, and without water, much less - 8 days. According to special medical experiments, with a loss of moisture in the amount of 6-8% of the body weight, a person falls into a semi-faint state, with a loss of 10%, hallucinations begin, at 12% a person can no longer recover without special medical care, and with a loss of 20%, inevitable death. Many animals adapt well to lack of moisture. The most famous and striking example of this is the "ship of the desert", the camel. He can live for a very long time in a hot desert without consuming drinking water and losing up to 30% of his original weight without affecting his performance. So, in one of the special tests, a camel worked for 8 days under the scorching summer sun, having lost 100 kg. from 450 kg. your starting weight. And when they brought him to the water, he drank 103 liters and regained his weight. It has been established that a camel can get up to 40 liters of moisture by transforming the fat accumulated in its hump. Desert animals such as jerboas and kangaroo rats do not use drinking water at all - they have enough moisture that they get from food, and water that is formed in their bodies during the oxidation of their own fat, just like camels. Plants consume even more water for their growth and development. A cabbage pump "drinks" more than one liter of water per day, one tree on average - more than 200 liters of water. Of course, this is a rather approximate figure - different tree species in different natural conditions consume very, very different amounts of moisture. So saxaul growing in the desert spends a minimum amount of moisture, and eucalyptus, which in some places is called a "pump tree", passes a huge amount of water through itself, and for this reason its plantings are used to drain swamps. This is how the swampy malarial lands of the Colchis lowland were turned into a prosperous territory.

Already, about 10% of the world's population lacks clean water. And if we consider that 800 million households in rural areas, where about 25% of all humanity live, do not have a water supply system, then the problem of "water hunger" becomes truly global in nature. It is especially acute in developing countries, where about 90% of the population uses poor water. Lack of clean water is becoming one of the most important factors limiting the progressive development of mankind.

Acquired questions about the protection of water resources

Water is used in all areas of human economic activity. It is almost impossible to name any production process that does not use water. Due to the rapid development of industry, the growth of the population of cities, water consumption is increasing. Of paramount importance are the issues of protecting water resources and sources from depletion, as well as from pollution by wastewater. Everyone knows the damage caused by wastewater to the inhabitants of reservoirs. Even more terrible for man and all life on Earth is the appearance in river waters of pesticides washed away from the fields. So the presence of 2.1 parts of the pesticide (endrin) in the water per billion parts of water is enough to kill all the fish in it. A huge threat to humanity is posed by untreated wastewater from settlements discharged into rivers. This problem is solved by being aware of such technological processes in which the waste water is not discharged into reservoirs, and after cleaning it returns to the technological process.

Currently, great attention is paid to the protection of the environment and, in particular, natural reservoirs. Given the importance of this problem, our country does not adopt a law on the protection and rational use of natural resources. The Constitution reads: "Citizens of Russia are obliged to protect nature, to protect its wealth."

Types of water

Bromine water -saturated solution of Br 2 in water (3.5% by weight Br 2). Bromic water is an oxidizing agent, a brominating agent in analytical chemistry.

Ammonia water -formed when raw coke oven gas comes into contact with water, which is concentrated due to cooling of the gas or is specially injected into it to wash out NH3. In both cases, the so-called weak, or scrubber, ammonia water is obtained. Distillation of this ammonia water with steam and subsequent reflux and condensation produces concentrated ammonia water (18 - 20% NH 3 by weight), which is used in the production of soda as a liquid fertilizer, etc.

1

Thirteenth chapter. About the smallest grain of matter

Arriving from school, Sasha asked not to be disturbed and locked herself in a room.
“Their class is preparing a performance for the last bell,” Masha explained. - Probably, they were asked to make congratulations to graduates and costumes for the concert.
An hour later, my mother still decided to look at her daughter. She expected to find the girl drawing or sewing, but Sasha just sat at the table and looked thoughtfully at the glass of water, which, apparently, had been prepared for watercolors.
Hearing a rustle, Sasha raised her eyes and asked:
- A glass of water is water?
“Of course,” my mother answered mechanically, not quite understanding what her daughter meant.
- Is half a glass also water?
- Why not? - Mom was surprised.
- And a drop of water is also water, and half a drop ... - Sasha continued. - How many parts can a drop of water be divided into? What's the smallest piece of water?
“The smallest piece of water is a water molecule,” Mom said.
“The molecule is probably so small that it can only be seen under a microscope,” suggested Sasha.
- No, you can't even see a molecule under a microscope. She is very, very small. And a huge number of molecules make up the water that stands in front of you.
- How many? - Sasha asked immediately.
- It's so big that it's hard to imagine. Someone calculated that there are more molecules in one glass of water than the number of glasses of water in all the seas, oceans, rivers and lakes of the Earth.
- Wow! .. - Sasha suddenly spoke in a whisper. - Amazing!
“The most amazing thing,” Mom said calmly, “is that even a single water molecule behaves in chemical reactions in the same way as any amount of water.
Sasha looked around.
- So, each substance has its own molecule? She asked. - And they are all the same tiny?
- There are different molecules among the crumbs: both more and less. But all of them, of course, are very small in comparison with the objects that surround us. True, it cannot be said that all substances are composed of molecules - there are other particles of matter. But you will find out about this in high school, and now let's get to work, otherwise your high school students will be left without a holiday.
Mom went out, and Sasha began to think where to start. It was necessary to draw a greeting card, inflate two balloons and sew sequins on the costume for the concert.
After some thought, she decided to tackle balloons first. Taking in more air, the girl began to inflate the first balloon. At first, the balloon was easily filled with air, but the further, the more the balloon increased in size, and it became more and more difficult to inflate it. Finally it became huge. Sasha, with a ball in her teeth, went up to her mother and mumbled:
- Mmmm, pmmmmmm ...
Mom quickly took out a strong thread and helped tie the ball. Taking it in hand, Sasha began to examine him from all sides. It seemed to her that the balloon was not inflated enough, and she tried to lightly press on it. The ball was very resilient, but still gave a little under Sasha's hand.
- Mom, look, I'm reducing air molecules!
“You're wrong,” Mom said. - First, air has no molecules. Air is a mixture of gases, and each of them has its own molecules. Secondly, you are not reducing the molecules, but the gaps between them.
- Are there gaps between the molecules? - Sasha was surprised.
- How could you inflate your balloon? After all, with each portion of air you are blowing new gas molecules into it. You've probably noticed that the gas in the balloon is slightly compressed compared to the surrounding air. Count how many exhalations you need to make to inflate the balloon.
Sasha took another ball. He soon became as big as the first. She could not speak, but from her gestures, my mother understood that she blew twice, ten times.
- At one time, a person exhales about one liter of air. But the volume of your ball, of course, is less than twenty liters - after all, this is about two buckets.
Sasha began to nod her head as a sign that she agreed with her mother. At that moment, the ball popped out of her mouth and began to frantically rush around the room.
- Molecules run out of the ball! - Sasha shouted. - They tickle me!
Mom laughed. Sasha picked up the fallen ball and sat down on the floor.
“There’s certainly no distance between molecules in the floor,” she said. - It doesn't shrink.
“Although solids and liquids hardly compress, they also have gaps between molecules, only not as large as in gases,” Mom said.
- And if the gas is compressed very strongly, it becomes solid? - suggested Sasha.
- Sure. This is exactly how dry ice is obtained from carbon dioxide, which is placed in boxes of ice cream. And if you put a piece of dry ice on the table, after a while it will evaporate and turn into gas again.
- Then why doesn't the table turn into gas? - Sasha asked sarcastically.
“Molecules are attracted to each other and repelled at the same time,” Mom said.
Noticing that Sasha was going to ask one more question, Mom continued:
- Why this is happening, I cannot explain to you yet. Even many students do not immediately understand this. But if attraction is stronger than repulsion, the substance is liquid or solid, and if it is weaker, it turns into gas. It depends on the substance itself and on the temperature: when heated, the attraction becomes weaker.
- Now I understand, - said Sasha, - why the water is boiling. By the way, let's have some tea.
“Okay,” Mom agreed. - By the way, Masha is baking a pie. And, in my opinion, he is already ready. Do you feel how delicious it smells?
- But Masha is baking a pie in the kitchen, why did the smell reach the room?
- It was molecules of substances that were released during baking arrived to us. Any molecules move all the time. In solids they move a little in one place, in liquids they move from place to place, and in gases they rush around rather quickly.
Maxim came, and Sasha began to tell him about the molecules.
- And I know what our class is like when we sit at our desks during the lesson. Me and riddle I remembered suitable:

- You mean frozen water that floats in ordinary liquid water?
- Sure! And when we walk, hand in hand, to the dining room, it looks like moving water, as if we were floating, - explained Maxim.
- When the lessons are over, we run to the schoolyard, and then it turns out, like in another riddle:

After drinking tea and pie, Sasha and Maxim went to paint. Sasha dipped the brush into a glass of water, then scored some paint on it. A bright drop fell on the table, Sasha wiped it off with a cloth. Then she dropped the same drop into the water. The droplet sank to the bottom and began to slowly spread.
“Probably, water molecules move in a glass and push paint molecules,” suggested Sasha. - Wow, molecules cannot be seen, but what they do is noticeable ...
She opened a chemical notebook, showed Maxim notes about what her mother had told her.

Test 2

1. In what expressions are we talking about a simple substance oxygen, and not about a chemical element

a) oxygen is part of the water; c) in copper (II) oxide, the mass fraction of oxygen is 20%;

b) oxygen is poorly soluble in water; d) oxygen is odorless and colorless.

2. Relative atomic mass of an element:

a) unit of measurement - g / mol b) is equal to the ratio of the mass of an atom to 1 amu.

c) dimensionless quantity d) is equal to the ratio of the mass of the atom to the mass of the atom of a carbon nuclide with a mass number of 12.

3. What does the chemical formula H 2 S0 4 show?
a) one molecule of sulfuric acid; b) the relative atomic mass of sulfuric acid;
c) the qualitative composition of sulfuric acid; d) the spatial structure of the sulfuric acid molecule.

4. What properties characterize both the molecule and the substance consisting of these molecules?
a) qualitative composition; b) electrical conductivity;

c) chemical properties; d) state of aggregation.

5. The atom of which element has a mass of 2.66. 10 -23 g?
a) sulfur b) oxygen c) nitrogen d) neon

6. What statements are true for the concept of "simple substance"?
a) the form of existence of a chemical element in nature;
b ) is a part of chemical compounds;
c) consists of atoms of the same type;
d) there are more simple substances than chemical elements.

7. Indicate the reaction schemes reflecting chemical phenomena *:
a) I 2 (k) → I 2 (d); 6) S + O 2 → SO 2;
c) Fe + Cu 2+ → Fe 2+ + Cu; d) H 2 O (g) → H 2 O (g).

8. Determine the simplest formula of a substance in which the mass fractions (%) of sodium, sulfur and oxygen are, respectively, equal to 29.1; 40.5 and 30.4:
a) Na 2 SO 3; b) Na 2 S0 4; c) Na 2 S 2 O 3; d) Nа 2 S 2 0 7.

9. The mass of the O 3 molecule is:
a) 16 amu 6) 32 amu c) 48 g) 7.97.10 -23 g

10. What is the formula of iron oxide, in which the mass fraction of iron is 2.333 times the mass fraction of oxygen?
a) FeO b) Fe 2 O 3 c) Fe 3 O 4 d) FeO 3

Test 3

1. Specify the unit of molar volume:
a) mol / l; b) g / mol; c) l; d) l / mol.

2. What statements are true for the Avogadro constant?
a) dimensionless quantity; 6) the unit of measurement is mol -1;
c) numerically equal to the number of atoms in 23 g of sodium; d) numerically equal to the number of molecules in 1 mol of substance

3. A mole is:
a) a unit of the amount of a substance; b) mass of 22.4 liters of gas under normal conditions;

c) the amount of a substance containing 6.02 · 10 23 structural units;

d) the ratio of the mass of a substance to its amount.

4. The mass of a molecule of a certain gas is 7.304 · 10 -23 g. What is the relative density of this gas: in terms of helium?
a) 10; 6) 11; at 12; d) 13;

5. The largest number of molecules at + 4 ° C and a pressure of 1 atm is contained in 10 liters:
a) water; b) hydrogen sulfide; c) hydrogen; d) hydrogen chloride.

6. In which of the indicated portions of the substance at and. at. contains the largest number of molecules?

a) 2 mol N 2; b) 44.8 L N 2 ; c) 132 g of CO 2; d) 0.018 L H 2 O.

7. The mass of 2 liters of gas (NU) is equal to 6.34 g. What is the molar mass of the gas?
a) 71; 6) 71 g; c) 35.5 g / mol; d) 71 g / mol.

8. In what volume of water at a pressure of 1.013 · 10 5 Pa and a temperature of + 4 ° C is 1 mol of a substance contained?
a) 22.4 l; 6) 18 ml; c) 36 ml; d) 0.018 ml.

9. For what gas is the density at i.u. is 1.63 g / l?
a) carbon monoxide (IV); b) ammonia; c) hydrogen chloride; d) methane.

10. The density of the gas for helium is 20. What is the mass of a gas molecule?
a) 80 g / mol; b) 80 a. eat.; c) 80 g; d) 1.33 10 -22 g

Test4

1. In which row are two complex substances and one simple one listed?

a) oxygen, nitrogen, water; c) hydrogen, bromine, carbon;

b) chlorine, ammonia, carbon dioxide; d) diamond, silicon oxide (IV), copper.

2. What statements are true for the concept "atom"?
a) the carrier of the chemical properties of the element;
b) collapses in chemical reactions;
c) chemically indivisible; d) electrically neutral.

3. Which expressions are correct?
a) sodium atom; c) an ammonia atom;

b) water molecule; d) oxygen molecule.

4. In what units can the masses of atoms and molecules be expressed?
a) d; b)and. eat.; in)kg; d)mole.

5. What phenomena involving water are accompanied by a chemical reaction?
a) freezing of water; c) evaporation of water;
b) dissolution of sodium in water; d) dissolution of sulfur oxide (IV) in water.

6. What is the unit of measure for relative molecular weight?
a) d; b ) g / mol; c) amu; d)it is a dimensionless quantity.

7. Chemical element- this is:
a) the kind of atoms with the same mass; b) the type of atoms with the same nuclear charge;
c) the smallest chemically indivisible particle of matter;
d) an electrically neutral particle, consisting of a positively charged nucleus and rotating ones; around it of negatively charged electrons.

8. A molecule cannot be said to be:
a) is preserved in chemical reactions; 6) the carrier of the chemical properties of the substance;
c) collapses in chemical reactions;
d) has the same qualitative composition as a substance consisting of these molecules.

9. What is the mass of a fluorine atom?
a) 19; b) 19 amu; c) 19 d; d) Z, 15 10 -26 kg

10. The mass of a phosphorus molecule under certain conditions is 1.03 · 10-26 g. How many phosphorus atoms are included in its molecule?
and) 2; 6) 4; c) H; d) 8.

Topic 2. Mole. Molar mass. Molar
volume. Relative gas density
Test 5

1. The molar mass is numerically equal to the mass:
a) one molecule of a substance;
6) 6.02.1023 structural units of matter;
c) 22.4 liters of gas (n.o.) *;
d) 1 mole of substance.

2. At n.u. 22.4 l is the volume:
a) 1 mole of any gas;
b) one molecule of any gas;
c) occupied by 6.02 · 10 23 gas molecules;
d) occupied by neon, weighing 40 g.

3. Specify the unit of molar mass:
a) d; b) mol -1 c) l / mol; d) g / mol.

4. The amount of a substance is not measured in:
a) amu; 6) d; c) mole; d) l / mol.

5. About the concept of "mole" it cannot be said that it is:
a) the mass of one molecule;
b) the mass is 6.02 · 10 23 molecules;
c) the number of particles in 1 mol of the substance;
d) the amount of a substance containing 6.02 · 10 23 structural units.

6. With the same mass and external conditions for different gases, the number of molecules is greater in the gas for which:
a) less molar mass; b) the value of the molar mass is greater;
c) more volume occupied by gas; d) less volume occupied by gas.

7. For which of the nitrogen oxides is the helium vapor density 7.5?
a) NO; b) N 2 O; c) NO 2. d) N 2 O 5

8. For what substances the volume is 1 mol at standard conditions. is 22.4 liters?
a) water; b) iodine; c) oxygen; d) nitrogen.

9. What is the number of atoms in 5.6 L (NU) ozone?
a) 1.51 10 23; 6) 3.01 * 10 23; c) 4.52 10 23; d) 6.02 10 23.

10. The hydrogen vapor density of sulfur under some conditions is 32. Indicate the formula of the sulfur molecule under these conditions:
a) S 8; b) S 4; c) S 2; d) S 6.

Topic 3. The structure of nuclei and electron shells
atoms. Isotopes
Test 6

1. Mark the symbols for the impossible energy sublevels:
a) 5s; 6) 3f; c) Зd; d) 1p.

2. Indicate the chemical sign of the element whose ground state atom has the largest number of half-filled orbitals:
a) C; b) Li; c) N; d) C1.

3. What is the difference between the atoms of the 19 40 K and 19 39 K nuclides?

a) Mass; b) the number of neutrons; c) the number of electrons; d) the number of protons.

4. What is the mass of an atom of the 7 15 N nuclide?
a) 7 amu; ... 6) 15 amu; ... c) 2.49. 10 _23 g; d) 1.16. 10 23 g

5. The abbreviated electronic configuration corresponds to the ground state of the Ca 2+ ion:
a)… 3S 2 3p 6 4s 2; b)… 3s 2 3p 6 4s 2 3d 2; c)… 3s 2 3p 6 4s 0; d) ... 3s 2 3p 4.

6. Note the electronic configuration of the atom of the nuclide 1 2 H:
a) 1s 2; b 1s 1; c) 1s 2 2s 1; d) 1s 2 2s 2.

7. Indicate the number of protons in non F:
a) 19; 6) 20; at 9; d) 10.

8. Acquiring two electrons, the oxygen atom turns into:
a) one of the isotopes of oxygen; 6) nitrogen atom;
c) a fluorine atom; d) non oxygen with the electron shell of neon.

9. How many electrons are at the pre-external energy level of the Cr atom in the ground state?
a) 2; 6) 1; c) 13; d) 12.

10. Indicate the mass of an atom containing 11 electrons and 12
Neutrons:
a) 12 amu; ... 6) 23 amu; ... c) 1.99. 10 23 g; d) 3.82. 10 -23.

Test 7

1. Indicate the number of neutrons in the nucleus of the 19 39 K nuclide:

a) 39; 6) 19; in 20; d) 58.

2. Note the schemes of excited states of atoms:
and) . ... .2S 2 2p 5 3s 1; 6). ... .3s 2 3p 6 4s 2 3d 1; in) . ... ... 3s 2 3p 6 4s 1; d) .. 4s 2 3d 4.

3. Among the listed electronic configurations, indicate the impossible ones:

a) 1s 2 2s 1; b)… 2s 2 2p 7; c)… 2s 2 2p 6; d) ... 3s 2 3p 6 4s 2 d 11.

4. How many orbitals are there in the third energy level?

a) 5; b) 2; at 3; d) 9.

5. Indicate the number of electrons at the external energy level of the copper atom in the ground state:

a) 2; b) 1; at 10 o'clock; d) 18.

6. Note the symbol for the energy sublevel with the highest energy in an electrically neutral atom:

a) 4a; b) 4p; c) 3p; d) 3s.

7. How many protons, neutrons and electrons are contained in the 35 Cl atom?

a) 37; b) 17; c) 52; d) 71.

8. What is the mass of tritium atoms:

a) 3 g; b) 3 amu; c) 2 amu; d) 4.98. 10 -24 g.

9. How many energy sublevels does the fourth energy level include?

a) 2; b) 3; in 1; d) 4.

10. How many electrons are there in the external energy level of the Cr ion?

a) 17; b) 7; at 8; d) 6.

Test 8

1. Which of the following electronic configurations correspond to a noble gas (n is the principal quantum number)?

a) ns 2 np 4; b) 1s 2; c) ns 2 np 6; d) ns 2 np 5.

2. How many electrons can be maximally located on the 5d - sublevel?

a) 3; b) 6; at 10 o'clock; d) 14.

3. An atom of which element can have the electronic configuration 1s 2 2s 2 2p 6 3s 1 3p 1?

a) sodium; b) magnesium; c) calcium; d) scandium.

4. The total number of electrons in the Cr 3+ ion is:

a) 21; b) 24; c) 27; d) 52.

5. How many fully filled energy levels are there in the atom of the element with atomic number 26?

a) 1; b) 2; at 3; d) 4.

6. Indicate the configuration of valence electrons in the Co atom in the ground state:

a) 3d 3 4s 1; b) 3d 10 4s 2; c) 4s 2 4d 7; d) 3d 7 4s 2.

7. How many neutrons are contained in a chlorine molecule formed by atoms of nuclides with a mass number of 35?

a) 18; b) 35; c) 36; d) 34.

8. What is the difference between the 16 O nuclide atom and the 16 O -2 ion?

a) the number of protons; b) the number of electrons; c) the number of neutrons; d) nuclear charge.

9. Indicate the names of the heaviest particle:

a) proton; b) neutron; c) a deuterium atom; d) protium atom.

10. Which element contains the same number of electrons as an ammonia molecule?

a) nitrogen; b) fluorine; c) neon; d) sodium.

Test 9

1. The nucleus of an atom 36 80 Kg contains:

a) 80 protons and 36 neutrons; b) 36 protons and 44 neutrons;

c) 36 protons and 44 neutrons; d) 36 protons and 80 neutrons.

2. Atoms of which elements contain two electrons at the external energy level?

a) chromium; b) manganese; c) vanadium; d) copper.

3. The phosphorus molecule contains 30 electrons. How many P atoms are in a molecule?

a) 2; b) 3; at 4; d) 5.

4. The E 3+ cation of some element has the electronic configuration 1s 2 2s 2 2p 6. How many atoms are there in the nucleus of an atom of a given element?

a) 10; b) 13; c) 16; d) 17.

5. The E 2 molecule contains 18 electrons. Specify the element symbol:

a) O; b) F; c) Ar; d) Cl.

6. For one atom of the nuclide 37 17 Oe there are three atoms of the nuclide 35 17 Oe. What is the average value of the relative atomic mass of the element?

a) 35.4; b) 35.5; c) 35.6; d) 35.7.

7. Eight (octet) electrons on the outer electron layer have atoms or ions:

a) Te -2; b) Ca; c) O -2; d) Mg 2+.

8. The total number of electrons and neutrons for the 45 21 Sc nuclide atom is:

a) 21; b) 24; c) 45; d) 66.

9. An ion containing 18 electrons and 16 protons has a charge equal to:

a) - 18; b) - 2; c) + 2; d) + 16.

10. Which particle has more protons than electrons?

a) sodium atom; b) sodium cation; c) a sulfur atom; d) sulfide ion S -2.

Test 10

1. The mass of an atom of some nuclide is 127 amu, the electron shell of an atom contains 53 electrons. How many neutrons are there in the nucleus of an atom of a given nuclide?

a) 127; b) 53; c) 180; d) 74.

2. Is the number the same for the atoms in the ground state of nuclides 1 9 40 K and 18 40 Ar?

a) mass; b) the number of protons; c) the number of electrons; d) the number of neutrons.

3. What is the difference between the electrons in the 1s and 3s orbitals?

a) energy; b) the shape of the atomic orbital;

c) the size of the atomic orbital; d) orientation of the atomic orbital in space.

4. When an electrically neutral atom turns into a cation, then:

a) the charge of the atom of the nucleus increases; b) the charge of the atomic nucleus does not change;

c) the number of electrons in the atom increases; d) the number of electrons in the atom decreases.

5. The pion atom, sodium cation and fluorine anion have the same:

a) the value of the mass; b) the number of neutrons; c) the number of electrons; d) the number of protons.

6. Mark the symbols of particles with the same distribution of electrons in energy sublevels:

a) O -2; b) Ne; c) N +5; d) Cl +7.

7. Ten electrons at the third energy level in the ground state contains an atom:

a) calcium; b) titanium; c) copper; d) chromium.

8. In the silicon atom in the main state there are completely unfilled orbitals:

a) 1; b) 6; at 5; d) 3.

9. The number of electrons and protons in the NO 3 ion is respectively equal to:

a) 14 and 48; b) 15 and 48; c) 32 and 31; d) 31 and 25.

10. The number of unpaired electrons in the ground state and of an atom with 24 protons in its nucleus is equal to:

Atoms in molecules communicate with each other due to the electromagnetic interactions of their constituent electrons and nuclei. This connection is not very "tough".

The model of a molecule, constructed from balls - atoms held together by rigid rods - does not look very much like a real molecule. In molecules, atoms are in continuous motion - they vibrate or rotate. But even this picture is inaccurate.

It would be more correct to say that not atoms move in a molecule, but their constituent nuclei and electrons.

Combining into molecules, atoms do not leave all their electrons around them. They either carry out a "redistribution" of electrons, while one of the atoms gives part of its electrons to another, positive and negative ions are formed, which "hold on to each other" due to Coulomb forces (ionic bond).

Or the atoms in the molecule begin to share some of their electrons (covalent bond). In either case, the atoms in the molecule cease to exist as such, they “lose their face”. But this picture is not entirely correct either.

After all, molecules, atoms, electrons and nuclei obey the laws of the microworld. This means that one cannot say about them: "They move this way or that way, they are there and there." It is necessary to describe their states in the language of quantum mechanics, and this is the “language of probabilities”.

Therefore, only the distribution densities of the particles constituting the molecule can be drawn. And in these pictures both common electron clouds and individual ions will indeed be visible.

It does not have an exact solution for the simplest molecule - the hydrogen molecule H2, consisting of four particles - two protons and two electrons. The exact solution is possible only for the two-body problem.

Therefore, for molecules, the Schrödinger equation is solved by approximate methods, and all calculations are carried out using computers. As an example, let us show the results of such calculations performed for lithium fluoride molecules LiF (ionic bond) and hydrogen H2 (covalent bond).

The figure shows a graph of the dependence of the system energy E on the distance R between the Li and F nuclei. In configuration b at R \u003d 8 A? (1 A? \u003d 10-10 m) the outer electron of the lithium atom passed to fluorine. This means that the state of two ions turned out to be energetically more favorable than the state of two atoms.

In state g at R \u003d 1.5 A? the energy of the system takes on a minimum value, this is the energetically most favorable state. The figure shows the results of similar calculations for the H atoms and the H2 molecule. The process of formation of a common electron shell around two H nuclei is clearly visible.

Substances. Molecules. Atoms