Oxygen physical properties. Oxygen: chemical properties of the element

Elements located in the main subgroup of group VI of the periodic table of elements of D. I. Mendeleev.

The distribution of electrons according to the energy equations of atoms of elements of the oxygen group Table 13

Element	Core charge	Energy levels					Atomic radius Å
		K	L	M	N	O
							0,60 1,04 1,16 1,43

Consideration of the atomic structures of the elements of the main subgroup of group VI shows that they all have a six-electron structure of the outer layer (Table 13) and, therefore, have relatively high electronegativity values. Has the highest electronegativity, the smallest -, which is explained by a change in the value of the atomic radius. The special place of oxygen in this group is emphasized by the fact that, and tellurium can directly combine with oxygen, but cannot combine with each other.

Elements of the oxygen group also belong to the number R-elements, since they are being completed R-shell. For all elements of the family, except for oxygen itself, 6 electrons of the outer layer are valence.
In redox reactions, elements of the oxygen group often exhibit oxidizing properties. The most strongly oxidizing properties are expressed in oxygen.
All elements of the main subgroup of group VI are characterized by a negative oxidation state of -2. However, for sulfur, selenium and tellurium, along with this, positive degrees oxidation (maximum +6).
The oxygen molecule, like any simple gas, is diatomic, built according to the type covalent bond formed by two electron pairs. Therefore, oxygen is divalent when a simple is formed.
Sulfur - solid... The molecule contains 8 sulfur atoms (S8), but they are connected in a kind of ring, in which each sulfur atom is connected only with two neighboring atoms by a covalent bond

Thus, each sulfur atom, having one common electron pair with two neighboring atoms, is itself divalent. Similar molecules form selenium (Se8) and tellurium (Te8).

■ 1. Make up a story about the oxygen group according to the following plan: a) position in periodic system; b) nuclear charges and. the number of neutrons in the nucleus; c) electronic configurations; d) structure crystal lattice; e) possible oxidation states of oxygen and all other elements of this group.
2. What are the similarities and differences in the atomic structures and electronic configurations of the atoms of the elements of the main subgroups of groups VI and VII?
3. How many valence electrons do the elements of the main subgroup of group VI have?
4. How should the elements of the main subgroup of group VI behave in redox reactions?
5. Which of the elements of the main subgroup of group VI is the most electronegative?

When considering the elements of the main subgroup of group VI, we first encounter the phenomenon of allotropy. The same element in the free state can form two or more simple substances. This phenomenon is called allotropy, and they themselves are called allotropic modifications.

Write this wording in your notebook.

For example, the element oxygen is able to form two simple ones - oxygen and ozone.
The formula of simple oxygen is O2, the formula of the simple substance of ozone is O3. Their molecules are built differently:

Oxygen and ozone are allotropic modifications of the element oxygen.
Sulfur can also form several allotropic modifications (modifications). Known rhombic (octahedral), plastic and monoclinic sulfur. Selenium and tellurium also form several allotropic modifications. It should be noted that the phenomenon of allotropy is characteristic of many elements. We will consider the differences in the properties of different allotropic modifications when studying the elements.

■ 6. What is the difference between the structure of an oxygen molecule and the structure of an ozone molecule?

7. What type of bond is in oxygen and ozone molecules?

Oxygen. Physical properties, physiological action, the importance of oxygen in nature

Oxygen is the lightest element of the main subgroup of group VI. The atomic weight of oxygen is 15.994. 31,988. The oxygen atom has the smallest radius of the elements of this subgroup (0.6 Å). Electronic configuration oxygen atom: ls 2 2s 2 2p 4.

The distribution of electrons over the orbitals of the second layer indicates that oxygen has two unpaired electrons in p orbitals, which can be easily used to form chemical bond between atoms. Characteristic oxidation state of oxygen.
Oxygen is a colorless and odorless gas. It is heavier than air, at a temperature of -183° it turns into a blue liquid, and at a temperature of -219° it solidifies.

The density of oxygen is 1.43 g/L. Oxygen is poorly soluble in water: 3 volumes of oxygen dissolve in 100 volumes of water at 0°C. Therefore, oxygen can be kept in a gasometer (Fig. 34) - a device for storing gases that are insoluble and slightly soluble in water. Most often, oxygen is stored in a gasometer.
The gasometer consists of two main parts: vessel 1, which serves to store gas, and a large funnel 2 with a tap and a long tube, reaching almost to the bottom of vessel 1 and serving to supply water to the device. Vessel 1 has three tubes: tube 3 with a ground inner surface is inserted, a funnel 2 with a tap, a gas outlet tube equipped with a tap is inserted into tube 4; tube 5 at the bottom serves to release water from the device when it is charging and discharging. In a charged gasometer vessel 1 is filled with oxygen. At the bottom of the vessel is located, into which the end of the tube of funnel 2 is lowered.

Rice. 34.
1 - vessel for gas storage; 2 - funnel for water supply; 3 - tube with ground surface; 4 - tube for removing gas; 5 - a tube for the release of water when charging the device.

If you need to get oxygen from the gasometer, first open the funnel valve and slightly compress the oxygen in the gasometer. Then the valve on the gas outlet tube is opened, through which oxygen displaced by water escapes.

In industry, oxygen is stored in steel cylinders in a compressed state (Fig. 35, a), or in liquid form in oxygen "tanks" (Fig. 36).

Rice. 35. Oxygen balloon

Write out from the text the names of devices designed to store oxygen.
Oxygen is the most common element. It makes up almost 50% of the weight of the entire earth's crust (Fig. 37). The human body contains 65% oxygen, which is part of various organic matter from which tissues and organs are built. Water contains about 89% oxygen. In the atmosphere, oxygen accounts for 23% by weight and 21% by volume. Oxygen is included in a wide variety of rocks (for example, limestone, chalk, marble CaCO3, sand SiO2), ores of various metals (magnetic iron ore Fe3O4, brown iron ore 2Fe2O3 nH2O, red iron ore Fe2O3, bauxite Al2O3 nH2O, etc.) . Oxygen is a constituent of most organic substances.

The physiological significance of oxygen is enormous. It is the only gas that living organisms can use for respiration. The lack of oxygen causes the cessation of vital processes and the death of the organism. Without oxygen, a person can live only a few minutes. When breathing, oxygen is absorbed, which takes part in the redox processes occurring in the body, and oxidation products of organic substances, carbon dioxide and other substances, are released. Both terrestrial and aquatic living organisms breathe oxygen: terrestrial - free oxygen of the atmosphere, and aquatic - oxygen dissolved in water.
In nature, a kind of oxygen cycle occurs. Oxygen from the atmosphere is absorbed by animals, plants, humans, is spent on the processes of fuel combustion, decay and other oxidative processes. Carbon dioxide and water produced during the oxidation process are consumed by green plants, in which, with the help of chlorophyll from leaves and solar energy the process of photosynthesis is carried out, i.e., the synthesis of organic substances from carbon dioxide and water, accompanied by the release of oxygen.
To provide oxygen to one person, the crowns of two large trees are needed. Green plants maintain a constant composition of the atmosphere.

■ 8. What is the importance of oxygen in the life of living organisms?
9. How is the supply of oxygen in the atmosphere replenished?

Chemical properties of oxygen

Free oxygen, reacting with simple and complex substances, usually behaves like.

Rice. 37.

The oxidation state that it acquires in this case is always -2. Many elements enter into direct interaction with oxygen, with the exception of noble metals, elements with electronegativity values ​​close to oxygen () and inert elements.
As a result, oxygen compounds with simple and complex substances are formed. Many burn in oxygen, although they either do not burn or burn very weakly in air. burns in oxygen with a bright yellow flame; in this case, sodium peroxide is formed (Fig. 38):
2Na + O2 = Na2O2,
Sulfur burns in oxygen with a bright blue flame to form sulfur dioxide:
S + O2 = SO2
Charcoal barely smolders in air, but in oxygen it becomes very hot and burns out with the formation of carbon dioxide (Fig. 39):
C + O2 = CO2

Rice. 36.

It burns in oxygen with a white, dazzlingly bright flame, and solid white phosphorus pentoxide is formed:
4P + 5O2 = 2P2O5
burns in oxygen, scattering sparks and forming iron scale (Fig. 40).
Burn in oxygen and organic substances, such as methane CH4, incoming composition natural gas: СH4 + 2O2 = CO2 + 2H2O
Combustion in pure oxygen is much more intense than in air, and makes it possible to obtain significantly higher temperatures. This phenomenon is used to intensify a number of chemical processes and more efficient fuel combustion.
In the process of respiration, oxygen, combining with blood hemoglobin, forms oxyhemoglobin, which, being a very unstable compound, easily decomposes in tissues with the formation of free oxygen, which is used for oxidation. Rotting is also an oxidative process involving oxygen.
They recognize pure oxygen by introducing a smoldering splinter into the vessel, where its presence is expected. It flashes brightly - this is a qualitative test for oxygen.

■ 10. How, having a splinter at your disposal, can you recognize oxygen and carbon dioxide in different vessels? 11. What volume of oxygen will be used to burn 2 kg of coal containing 70% carbon, 5% hydrogen, 7% oxygen, and the rest are non-combustible components?

Rice. 38. burning sodium Rice. 39. burning coal Rice. 40. Combustion of iron in oxygen.

12. Will 10 liters of oxygen be enough to burn 5 g of phosphorus?
13. 1 m3 of a gas mixture containing 40% carbon monoxide, 20% nitrogen, 30% hydrogen and 10% carbon dioxide was burned in oxygen. How much oxygen was consumed?
14. Is it possible to dry oxygen by passing it through: a) sulfuric acid, b) calcium chloride, c) phosphoric anhydride, d) metallic ?
15. How to free carbon dioxide from oxygen impurities and vice versa, how to free oxygen from carbon dioxide impurities?
16. 20 liters of oxygen containing an admixture of carbon dioxide were passed through 200 ml of 0.1 n. barium solution. As a result, the Ba 2+ cation was completely precipitated. How much carbon dioxide (in percent) did the original oxygen contain?

Obtaining oxygen

Oxygen is obtained in several ways. In the laboratory, oxygen is obtained from oxygen-containing substances that can easily split it off, for example, from potassium permanganate KMnO4 (Fig. 41) or from bertolet salt KClO3:
2KMnO4 = K2MnO4 + MnO2 + O2

2KSlO3 = 2KSl + O2
When obtaining oxygen from Bertolet salt, a catalyst, manganese dioxide, must be present to accelerate the reaction. The catalyst accelerates decomposition and makes it more uniform. Without a catalyst

Rice. 41. A device for obtaining oxygen in a laboratory way from potassium permanganate. 1 - potassium permanganate; 2 - oxygen; 3 - cotton wool; 4 - cylinder - collection.

an explosion occurs if Bertolet salt is taken in large quantities and especially if it is contaminated with organic substances.
Oxygen is also obtained from hydrogen peroxide in the presence of a catalyst - manganese dioxide MnO2 according to the equation:
2H2O2[MnO2] = 2H2O + O2

■ 17. Why is MnO2 added during the decomposition of Berthollet salt?
18. Oxygen formed during the decomposition of KMnO4 can be collected over water. Reflect this in the device diagram.
19. Sometimes, in the absence of manganese dioxide in the laboratory, a little residue is added to Bertolet's salt instead of it after calcination of potassium permanganate. Why is such a change possible?
20. What volume of oxygen will be released during the decomposition of 5 moles of Bertolet salt?

Oxygen can also be obtained by decomposition of nitrates when heated above the melting point:
2KNO3 = 2KNO2 + O2
In industry, oxygen is obtained mainly from liquid air. translated into liquid state the air is evaporated. First, it evaporates (its boiling point is 195.8°), and oxygen remains (its boiling point is -183°). In this way, oxygen is obtained almost in pure form.
Sometimes, in the presence of cheap electricity, oxygen is obtained by electrolysis of water:
H2O ⇄ H + + OH -
H++ e— → H 0
at the cathode
2OH — — e— → H2O + O; 2O = O2
at the anode

■ 21. List laboratory and industrial methods receiving oxygen. Write them down in a notebook, accompanying each method with a reaction equation.
22. Are the reactions used to produce oxygen redox? Give a reasoned answer.
23. Taken 10 g of the following substances; potassium permanganate, potassium chloride, potassium nitrate. In which case will it be possible to obtain the largest amount of oxygen?
24. In oxygen obtained by heating 20 g of potassium permanganate, 1 g of coal was burned. What percentage of permanganate has been decomposed?

Oxygen is the most common element in nature. It is widely used in medicine, chemistry, industry, etc. (Fig. 42).

Rice. 42. The use of oxygen.

Pilots at high altitudes, people working in an atmosphere of harmful gases, employed in underground and underwater work, use oxygen devices (Fig. 43).

In cases where it is difficult due to a particular disease, a person is allowed to breathe pure oxygen from an oxygen bag or placed in an oxygen tent.
Currently, oxygen-enriched air or pure oxygen is widely used to intensify metallurgical processes. Oxy-hydrogen and oxygen-acetylene torches are used for welding and cutting metals. By impregnating liquid oxygen with combustible substances: sawdust, coal powder, etc., explosive mixtures are obtained, called oxyliquites.

■ 25. Draw a table in your notebook and complete it.

Ozone O3

As already mentioned, the element oxygen can form another allotropic modification - ozone O3. Ozone boils at -111° and solidifies at -250°. It is blue in the gaseous state and blue in the liquid state. ozone in water is much higher than oxygen: 45 volumes of ozone dissolve in 100 volumes of water.

Ozone differs from oxygen in that its molecule consists of three rather than two atoms. In this regard, the oxygen molecule is much more stable than the ozone molecule. Ozone breaks down easily according to the equation:
O3 = O2 + [O]

The release of atomic oxygen during the decay of ozone makes it a much stronger oxidizing agent than oxygen. Ozone has a fresh smell (“ozone” in translation means “odorous”). In nature, it is formed under the action of a quiet electric discharge and in pine forests. Patients with lung disease are advised to spend more time in pine forests. However, prolonged exposure to an atmosphere highly enriched with ozone can have a toxic effect on the body. Poisoning is accompanied by dizziness, nausea, bleeding from the nose. In chronic poisoning, heart disease can occur.
In the laboratory, ozone is obtained from oxygen in ozonizers (Fig. 44). Oxygen is passed into the glass tube 1, wound on the outside with wire 2. Wire 3 passes inside the tube. Both of these wires are connected to the poles of a current source that creates a high voltage on these electrodes. A quiet electrical discharge occurs between the electrodes, due to which ozone is formed from oxygen.

Figure 44; Ozonator. 1 - glass bottle; 2 - outer winding; 3 - wire inside the tube; 4 - solution of potassium iodide with starch

3O2 = 2O3
Ozone is a very strong oxidizing agent. It is much more energetic than oxygen, enters into reactions and is generally much more active than oxygen. For example, unlike oxygen, it can displace from hydrogen iodide or iodine salts:
2KI + O3 + H2O = 2KOH + I2 + O2

There is very little ozone in the atmosphere (about one millionth of a percent), but it plays a significant role in absorbing ultraviolet sunlight, so they fall on the ground in smaller quantities and do not have a detrimental effect on living organisms.
Ozone is used in small quantities mainly for air conditioning and also in chemistry.

■ 26. What are allotropic modifications?
27. Why does starch iodine paper turn blue when exposed to ozone? Give a reasoned answer.
28. Why is the oxygen molecule much more stable than the ozone molecule? Justify your answer in terms of intramolecular structure.

8 O 1s 2 2s 2 2p 4 ; A r = 15.999 Isotopes: 16 O (99.759%); 17 O (0.037%); 18 O (0.204%); EO - 3.5

Clark in earth's crust 47% by weight; in the hydrosphere 85.82% by weight; in the atmosphere 20.95% by volume.

The most common element.

Forms of finding the element: a) in free form - O 2, O 3;

b) in bound form: O 2- anions (mainly)

Oxygen is a typical non-metal, p-element. Valency = II; oxidation state -2 (except for H 2 O 2, OF 2, O 2 F 2)

Physical properties of O 2

Molecular oxygen O 2 under normal conditions is in a gaseous state, has no color, smell and taste, and is slightly soluble in water. Upon deep cooling under pressure, it condenses into a pale blue liquid (Tbp - 183 ° C), which at -219 ° C turns into blue crystals.

Methods of obtaining

1. Oxygen is formed in nature in the process of photosynthesis mCO 2 + nH 2 O → mO 2 + Cm (H 2 O) n

2. Industrial production

a) rectification of liquid air (separation from N 2);

b) water electrolysis: 2H 2 O → 2H 2 + O 2

3. In the laboratory, they are obtained by thermal redox decomposition of salts:

a) 2KSlO 3 \u003d 3O 2 + 2KCI

b) 2KMnO 4 \u003d O 2 + MnO 2 + K 2 MnO 4

c) 2KNO 3 \u003d O 2 + 2KNO 2

d) 2Cu (NO 3) O 2 \u003d O 2 + 4NO 2 + 2CuO

e) 2AgNO 3 \u003d O 2 + 2NO 2 + 2Ag

4. In hermetically sealed rooms and in autonomous breathing apparatus, oxygen is obtained by the reaction:

2Na 2 O 2 + 2СO 2 \u003d O 2 + 2Na 2 CO 3

Chemical properties of oxygen

Oxygen is a strong oxidizing agent. By chemical activity second only to fluorine. Forms compounds with all elements except He, Ne and Ag. Reacts directly with most simple substances under normal conditions or when heated, as well as in the presence of catalysts (with the exception of Au, Pt, Hal 2, noble gases). Reactions involving O 2 are in most cases exothermic, often proceeding in the combustion mode, sometimes in an explosion. As a result of reactions, compounds are formed in which oxygen atoms, as a rule, have C.O. -2:

Alkali metal oxidation

4Li + O 2 = 2Li 2 O lithium oxide

2Na + O 2 \u003d Na 2 O 2 sodium peroxide

K + O 2 \u003d KO 2 potassium superoxide

Oxidation of all metals except Au, Pt

Me + O 2 = Me x O y oxides

Oxidation of non-metals, except halogens and noble gases

N 2 + O 2 \u003d 2NO - Q

S + O 2 \u003d SO 2;

C + O 2 \u003d CO 2;

4P + 5O 2 \u003d 2P 2 O 5

Si + O 2 \u003d SiO 2

Oxidation of hydrogen compounds of non-metals and metals

4HI + O 2 \u003d 2I 2 + 2H 2 O

2H 2 S + 3O 2 \u003d 2SO 2 + 2H 2 O

4NH 3 + 3O 2 \u003d 2N 2 + 6H 2 O

4NH 3 + 5O 2 \u003d 4NO + 6H 2 O

2PH 3 + 4O 2 \u003d P 2 O 5 + 3H 2 O

SiH 4 + 2O 2 \u003d SiO 2 + 2H 2 O

C x H y + O 2 = CO 2 + H 2 O

MeH x + 3O 2 \u003d Me x O y + H 2 O

Oxidation of lower oxides and hydroxides of polyvalent metals and nonmetals

4FeO + O 2 \u003d 2Fe 2 O 3

4Fe(OH) 2 + O 2 + 2H 2 O = 4Fe(OH) 3

2SO 2 + O 2 = 2SO 3

4NO 2 + O 2 + 2H 2 O \u003d 4HNO 3

Oxidation of metal sulfides

4FeS 2 + 11О 2 = 8SO 2 + 2Fe 2 О 3

Oxidation of organic substances

All organic compounds burn, being oxidized by atmospheric oxygen.

The products of oxidation of various elements included in their molecules are:

In addition to reactions of complete oxidation (combustion), partial oxidation reactions are also possible.

Examples of reactions of incomplete oxidation of organic substances:

1) catalytic oxidation of alkanes

2) catalytic oxidation of alkenes

3) oxidation of alcohols

2R-CH 2 OH + O 2 → 2RCOH + 2H 2 O

4) oxidation of aldehydes

Ozone

Ozone O 3 is a stronger oxidizing agent than O 2, since during the reaction its molecules decompose to form atomic oxygen.

Pure O 3 - gas of blue color, very poisonous.

K + O 3 \u003d KO 3 potassium ozonide, red.

PbS + 2O 3 \u003d PbSO 4 + O 2

2KI + O 3 + H 2 O \u003d I 2 + 2KOH + O 2

The latter reaction is used for the qualitative and quantitative determination of ozone.

Oxygen is a chemical element whose properties will be discussed in the next few paragraphs. Let's turn to the Periodic System chemical elements DI. Mendeleev. The element oxygen is located in period 2, group VI, the main subgroup. It also states that the relative atomic mass oxygen is 16. By serial number oxygen in the Periodic System, you can easily determine the number of electrons contained in its atom, the nuclear charge of the oxygen atom, the number of protons. The valency of oxygen in most compounds is II. An oxygen atom can attach two electrons and turn into an ion: O0 + 2ē = O−2. It is worth noting that oxygen is the most common element on our planet. Oxygen is part of the water. Marine and fresh water 89% by mass are composed of oxygen. Oxygen is found in many minerals and rocks. The mass fraction of oxygen in the earth's crust is about 47%. Air contains about 23% oxygen by mass.

Physical properties of oxygen

When two oxygen atoms interact, a stable molecule of a simple oxygen substance O2 is formed. This simple substance, like the element, is called oxygen. Do not confuse oxygen as an element and oxygen as a simple substance! The physical properties of oxygen It is a colorless, odorless and tasteless gas. Practically insoluble in water (at room temperature and normal atmospheric pressure, the solubility of oxygen is about 8 mg per liter of water). Oxygen is soluble in water - 31 ml of oxygen (0.004% by mass) dissolves in 1 liter of water at a temperature of 20 ° C. However, this amount is sufficient for the respiration of fish living in water bodies. Gaseous oxygen is slightly heavier than air: 1 liter of air at 0°C and normal pressure weighs 1.29 g, and 1 liter of oxygen weighs 1.43 g. Oxygen exhibits interesting properties when strongly cooled. So, at a temperature -183°C oxygen condenses into a clear mobile liquid of a pale blue color. If liquid oxygen is cooled even more, then at a temperature -218°C oxygen "freezes" in the form of blue crystals. If the temperature is gradually raised, then -218°С, solid oxygen will begin to melt, and when -183°C- boil. Therefore, the boiling and condensation points, as well as the freezing and melting points for substances, are the same. Dewar vessels are used to store and transport liquid oxygen.... Dewar vessels are used for storage and transportation of liquids, the temperature of which must remain constant for a long time. The Dewar vessel bears the name of its inventor, the Scottish physicist and chemist James Dewar. The simplest Dewar vessel is a household thermos. The device of the vessel is quite simple: it is a flask placed in a large flask. Air is evacuated from the sealed space between the flasks. Due to the absence of air between the walls of the flasks, the liquid poured into the inner flask does not cool or heat up for a long time.

Oxygen is a paramagnetic substance, that is, in liquid and solid states, it is attracted by a magnet.

In nature, there is another simple substance, consisting of oxygen atoms. This is ozone. Chemical formula ozone O3. Ozone, like oxygen, is a gas under normal conditions. Ozone is formed in the atmosphere during lightning discharges. The characteristic smell of freshness after a thunderstorm is the smell of ozone. If ozone is obtained in the laboratory and a significant amount of it is collected, then in high concentrations ozone will have a sharp unpleasant odor. Ozone is obtained in the laboratory in special devices - ozonators. Ozonator- a glass tube into which a current of oxygen is supplied, and an electric discharge is created. An electrical discharge turns oxygen into ozone: Unlike colorless oxygen, ozone is a blue gas. The solubility of ozone in water is about 0.5 liters of gas per 1 liter of water, which is much higher than that of oxygen. Given this property, ozone is used for disinfection drinking water, as it has a detrimental effect on pathogens. At low temperatures, ozone behaves similarly to oxygen. At a temperature of –112°C, it condenses into a violet liquid, and at a temperature of –197°C, it crystallizes in the form of dark purple, almost black crystals. Thus, we can conclude that atoms of the same chemical element can form different simple substances .

The phenomenon of the existence of a chemical element in the form of several simple substances is called allotropy.

Simple substances formed by the same element are called allotropic modifications

Means, oxygen and ozone are allotropic modifications of the chemical element oxygen. There is evidence that at ultra-low temperatures, in a liquid or solid state, oxygen can exist in the form of O4 and O8 molecules.

The oxygen cycle in nature

The amount of oxygen in the atmosphere is constant. Consequently, the expended oxygen is constantly replenished with new. The most important sources of oxygen in nature are carbon dioxide and water. Oxygen enters the atmosphere mainly as a result of the photosynthesis process that occurs in plants, according to the reaction scheme:

CO2 + H2O → C6H12O6 + O2.

Oxygen can be formed in upper layers Earth's atmosphere: due to exposure to solar radiation, water vapor partially decomposes with the formation of oxygen. Oxygen is consumed during respiration, fuel combustion, oxidation of various substances in living organisms, and oxidation of inorganic substances found in nature. A large number of oxygen is consumed in technological processes such as, for example, steel smelting. The oxygen cycle in nature can be represented as a diagram:

• Oxygen- an element of group VI, the main subgroup, 2 periods of the Periodic System of D.I. Mendeleev
• The element oxygen forms in nature two allotropic modifications: oxygen O2 and ozone O3
• The phenomenon of the existence of a chemical element in the form of several simple substances is called allotropy
• Simple substances are called allotropic modifications
• Oxygen and ozone have different physical properties
• Oxygen- a colorless gas, odorless, tasteless, practically insoluble in water, at a temperature of -183 ° C it condenses into a pale blue liquid. At -218°C crystallizes in the form of blue crystals
• Ozone- a blue gas with a pungent odor. Let's well dissolve in water. At -112°С, it condenses into a violet liquid, crystallizes as dark violet, almost black crystals, at -197°С
• Liquid oxygen, ozone and other gases are stored in Dewar flasks

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The processes of combustion and respiration have long attracted the attention of scientists. The first indications that not all air, but only its "active" part supports combustion, were found in Chinese manuscripts of the 8th century. Much later, Leonardo da Vinci (1452-1519) considered air as a mixture of two gases, only one of which is consumed during combustion and breathing. The final opening of the two main component parts air - nitrogen and oxygen, which made an era in science, occurred only at the end of the 18th century. Oxygen was obtained almost simultaneously by K. Scheele (1769-70) by calcining saltpeter (KNO 3 , NaNO 3), manganese dioxide MnO 2 and other substances and J. Priestley (1774) by heating minium Pb 3 O 4 and mercury oxide HgO. In 1772, D. Rutherford discovered nitrogen. In 1775, A. Lavoisier, having made a quantitative analysis of air, found that it “consists of two (gases) of a different and, so to speak, opposite nature,” that is, of oxygen and nitrogen. Based on broad experimental studies Lavoisier correctly explained combustion and respiration as processes of interaction between substances and oxygen. Since oxygen is part of acids, Lavoisier called it oxygene, that is, "former of acids" (from the Greek oxys - sour and gennao - I give birth; hence the Russian name "oxygen").

Distribution of oxygen in nature. Oxygen is the most common chemical element on Earth. The bound oxygen makes up about 6/7 of the mass of the Earth's water shell - the hydrosphere (85.82% by mass), almost half of the lithosphere (47% by mass), and only in the atmosphere, where oxygen is in a free state, does it take second place (23 .15% by weight) after nitrogen.

Oxygen also comes first in terms of the number of minerals it forms (1364); Among the minerals containing oxygen, silicates (feldspars, micas, and others), quartz, iron oxides, carbonates, and sulfates predominate. In living organisms, on average, about 70% oxygen; it is one of the most important organic compounds(proteins, fats, carbohydrates, etc.) and in the composition inorganic compounds skeleton. The role of free oxygen in biochemical and physiological processes, especially in respiration, is exceptionally important. With the exception of some anaerobic microorganisms, all animals and plants obtain the energy necessary for their life activity due to the biological oxidation of various substances with the help of oxygen.

The entire mass of free Oxygen of the Earth arose and is preserved due to the vital activity of green plants on land and the World Ocean, which release Oxygen in the process of photosynthesis. On the earth's surface, where photosynthesis proceeds and free oxygen predominates, sharply oxidizing conditions are formed. On the contrary, in magma, as well as deep horizons groundwater, in the silts of the seas and lakes, in swamps, where there is no free oxygen, a reducing environment is formed. Oxidation-reduction processes involving oxygen determine the concentration of many elements and the formation of mineral deposits - coal, oil, sulfur, iron ores, copper, etc. economic activity person. In some industrialized countries, the combustion of fuel consumes more oxygen than plants produce during photosynthesis. In total, about 9·10 9 tons of oxygen is consumed annually for fuel combustion in the world.

Isotopes, atom and molecule of oxygen. Oxygen has three stable isotopes: 16 O, 17 O and 18 O, the average content of which is respectively 99.759%, 0.037% and 0.204% of the total oxygen atoms on earth. The sharp predominance of the lightest of them, 16 O, in the mixture of isotopes is due to the fact that the nucleus of the 16 O atom consists of 8 protons and 8 neutrons. And such nuclei, as follows from the theory of the atomic nucleus, have a special stability.

In accordance with the position of Oxygen in the periodic system of elements of Mendeleev, the electrons of the Oxygen atom are located on two shells: 2 - on the inner and 6 - on the outer (configuration 1s 2 2s 2 2p 4). Insofar as outer shell the oxygen atom is not filled, and the ionization potential and electron affinity are respectively 13.61 and 1.46 eV, the oxygen atom in chemical compounds usually acquires electrons and has a negative effective charge. On the contrary, extremely rare are compounds in which electrons are detached (more precisely, pulled away) from the oxygen atom (for example, F 2 O, F 2 O 3). Previously, based solely on the position of Oxygen in the periodic system, the oxygen atom in oxides and in most other compounds was assigned a negative charge (-2). However, as experimental data show, the O 2- ion does not exist either in the free state or in compounds, and the negative effective charge of the oxygen atom practically never significantly exceeds unity.

Under normal conditions, the oxygen molecule is diatomic (O 2); in a quiet electrical discharge a triatomic molecule O 3 is also formed - ozone; at high pressures, O 4 molecules are found in small amounts. The electronic structure of O 2 is of great theoretical interest. In the ground state, the O 2 molecule has two unpaired electrons; the "ordinary" classical structural formula O=O with two two-electron bonds. An exhaustive explanation of this fact is given within the framework of the theory of molecular orbitals. The ionization energy of the oxygen molecule (O 2 - e → O 2 +) is 12.2 eV, and the electron affinity (O 2 + e → O 2 -) is 0.94 eV. The dissociation of molecular oxygen into atoms at ordinary temperature is negligible, it becomes noticeable only at 1500°C; at 5000°C the oxygen molecules are almost completely dissociated into atoms.

Physical properties of oxygen. Oxygen is a colorless gas that condenses at -182.9°C and normal pressure to a pale blue liquid, which solidifies at -218.7°C to form blue crystals. The density of gaseous oxygen (at 0°C and normal pressure) is 1.42897 g/l. The critical temperature of oxygen is quite low (Tcrit = -118.84°C), that is, lower than that of Cl 2 , CO 2 , SO 2 and some other gases; T crit \u003d 4.97 MN / m 2 (49.71 at). Thermal conductivity (at 0°C) 23.86·10 -3 W/(m·K). Molar heat capacity (at 0°C) in j/(mol K) C p = 28.9, C v = 20.5, C p / C v = 1.403. The dielectric constant of gaseous oxygen is 1.000547 (0°C), liquid 1.491. Viscosity 189 mpoise (0°C). Oxygen is slightly soluble in water: at 20°C and 1 atm, 0.031 m 3 is dissolved in 1 m 3 of water, and at 0° C - 0.049 m 3 of oxygen. Good solid oxygen absorbers are platinum black and active charcoal.

Chemical properties of oxygen. Oxygen forms chemical compounds with all elements except light inert gases. Being the most active (after fluorine) non-metal, oxygen interacts directly with most elements; the exceptions are heavy inert gases, halogens, gold and platinum; their compounds with oxygen are obtained indirectly. Almost all reactions of oxygen with other substances - oxidation reactions are exothermic, that is, they are accompanied by the release of energy. Oxygen reacts extremely slowly with hydrogen at ordinary temperatures; above 550°C, this reaction proceeds with an explosion:

2H 2 + O 2 \u003d 2H 2 O.

Oxygen reacts very slowly with sulfur, carbon, nitrogen, and phosphorus under normal conditions. With an increase in temperature, the reaction rate increases and at a certain ignition temperature characteristic of each element, combustion begins. The reaction of nitrogen with oxygen due to the special strength of the N 2 molecule is endothermic and becomes noticeable only above 1200 ° C or in an electric discharge: N 2 + O 2 = 2NO. Oxygen actively oxidizes almost all metals, especially alkali and alkaline earth metals. The activity of the interaction of metal with oxygen depends on many factors - the state of the metal surface, the degree of grinding, the presence of impurities.

In the process of interaction of a substance with oxygen, the role of water is extremely important. For example, even this active metal, like potassium, does not react with Oxygen completely devoid of moisture, but ignites in Oxygen at ordinary temperature in the presence of even negligible amounts of water vapor. It is estimated that up to 10% of all metal produced is lost annually as a result of corrosion.

Oxides of some metals, by adding oxygen, form peroxide compounds containing 2 or more oxygen atoms bonded to each other. So, peroxides Na 2 O 2 and BaO 2 include peroxide ion O 2 2-, superoxides NaO 2 and KO 2 - ion O 2 -, and ozonides NaO 3, KO 3, RbO 3 and CsO 3 - ion O 3 -. Oxygen reacts exothermically with many complex substances. So, ammonia burns in oxygen in the absence of catalysts, the reaction proceeds according to the equation: 4NH 3 + 3O 2 \u003d 2N 2 + 6H 2 O. Oxidation of ammonia with oxygen in the presence of a catalyst gives NO (this process is used to obtain nitric acid). Special meaning has combustion of hydrocarbons (natural gas, gasoline, kerosene) - the most important source heat in everyday life and industry, for example, CH 4 + 2O 2 \u003d CO 2 + 2H 2 O. The interaction of hydrocarbons with oxygen underlies many of the most important production processes- such is, for example, the so-called conversion of methane, carried out to produce hydrogen: 2CH 4 + O 2 + 2H 2 O \u003d 2CO 2 + 6H 2. Many organic compounds (hydrocarbons with double or triple bonds, aldehydes, phenols, as well as turpentine, drying oils, and others) actively add oxygen. Oxidation with oxygen nutrients in cells serves as a source of energy for living organisms.

Getting Oxygen. There are 3 main ways to obtain oxygen: chemical, electrolysis (electrolysis of water) and physical (air separation).

The chemical method was invented earlier than others. Oxygen can be obtained, for example, from Bertolet salt KClOz, which decomposes when heated, releasing O 2 in an amount of 0.27 m 3 per 1 kg of salt. Barium oxide BaO, when heated to 540°C, first absorbs oxygen from the air, forming BaO 2 peroxide, and upon subsequent heating to 870°C, BaO 2 decomposes, releasing pure oxygen. It can also be obtained from KMnO 4 , Ca 2 PbO 4 , K 2 Cr 2 O 7 and other substances by heating and adding catalysts. The chemical method of obtaining oxygen is inefficient and expensive, has no industrial significance and is used only in laboratory practice.

The electrolysis method consists in passing a direct electric current through water, to which a solution of caustic soda NaOH is added to increase its electrical conductivity. In this case, water decomposes into oxygen and hydrogen. Oxygen is collected near the positive electrode of the cell, and hydrogen - near the negative. In this way, oxygen is extracted as a by-product in the production of hydrogen. To obtain 2 m 3 of hydrogen and 1 m 3 of oxygen, 12-15 kWh of electricity is consumed.

Air separation is the main way to obtain oxygen in modern technology... It is very difficult to carry out the separation of air in a normal gaseous state, therefore, the air is first liquefied, and only then divided into its component parts. This method of obtaining oxygen is called air separation by deep cooling. First, the air is compressed by a compressor, then, after passing through the heat exchangers, it expands in an expander machine or a throttle valve, as a result of which it is cooled to a temperature of 93 K (-180 ° C) and turns into liquid air. Further separation of liquid air, consisting mainly of liquid nitrogen and liquid oxygen, is based on the difference in the boiling point of its components [T bp O 2 90.18 K (-182.9 ° C), t bp N 2 77.36 K (- 195.8°C)]. With the gradual evaporation of liquid air, nitrogen is first evaporated, and the remaining liquid becomes more and more enriched with oxygen. By repeating this process many times on the distillation plates of the air separation columns, liquid oxygen of the required purity (concentration) is obtained. The USSR manufactures small (several liters) and the world's largest oxygen air separation plants (35,000 m 3 /h of oxygen). These units produce technological Oxygen with a concentration of 95-98.5%, technical Oxygen with a concentration of 99.2-99.9% and purer, medical Oxygen, dispensing products in liquid and gaseous form. The consumption of electrical energy is from 0.41 to 1.6 kWh/m 3 .

Oxygen can also be obtained by separating air by the method of selective penetration (diffusion) through membrane partitions. High-pressure air is passed through fluoroplastic, glass or plastic partitions, the structural lattice of which is capable of passing the molecules of some components and retaining others.

Gaseous oxygen is stored and transported in steel cylinders and receivers at a pressure of 15 and 42 MN/m2 (150 and 420 bar, respectively, or 150 and 420 atm), liquid oxygen in metal Dewar vessels or in special tank-tanks. Special pipelines are also used to transport liquid and gaseous oxygen. Oxygen cylinders are painted blue and have a black inscription "oxygen".

The use of oxygen. Technical oxygen is used in the processes of flame treatment of metals, in welding, oxygen cutting, surface hardening, metallization, and others, as well as in aviation, on submarines, and so on. Technological oxygen is used in the chemical industry in the production of artificial liquid fuels, lubricating oils, nitric and sulfuric acids, methanol, ammonia and ammonia fertilizers, metal peroxides and other chemical products. Liquid oxygen is used in blasting, in jet engines, and in laboratory practice as a refrigerant.

Pure oxygen enclosed in cylinders is used for breathing at high altitudes, during space flights, during scuba diving, etc. . P.

Oxygen is widely used in metallurgy to intensify a number of pyrometallurgical processes. Complete or partial replacement of the air entering the metallurgical units with oxygen has changed the chemistry of the processes, their thermal parameters and technical and economic indicators. Oxygen blast made it possible to reduce heat losses with outgoing gases, a significant part of which during air blast was nitrogen. Not taking a significant part in chemical processes, nitrogen slowed down the course of reactions, reducing the concentration of active reagents in the redox medium. When purged with oxygen, fuel consumption is reduced, the quality of the metal is improved, it is possible to obtain new types of products in metallurgical units (for example, slags and gases of an unusual composition for this process, which find special technical applications), etc.

The first experiments on the use of oxygen-enriched blast in blast-furnace production for the smelting of pig iron and ferromanganese were carried out simultaneously in the USSR and Germany in 1932-33. The increased oxygen content in the blast furnace is accompanied by a large reduction in the consumption of the latter, while the content of carbon monoxide in the blast furnace gas increases and its heat of combustion increases. Oxygen enrichment of the blast makes it possible to increase the productivity of the blast furnace, and in combination with gaseous and liquid fuel supplied to the hearth, it leads to a reduction in coke consumption. In this case, for each additional percentage of Oxygen in the blast, the productivity increases by about 2.5%, and the coke consumption decreases by 1%.

Oxygen in open-hearth production in the USSR was first used to intensify fuel combustion (on an industrial scale, oxygen was first used for this purpose at the Sickle and Hammer and Krasnoye Sormovo plants in 1932-33). In 1933 they began to blow oxygen directly into the liquid bath in order to oxidize impurities during the finishing period. With an increase in the intensity of melt blowing by 1 m 3 /t per 1 hour, the productivity of the furnace increases by 5-10%, fuel consumption is reduced by 4-5%. However, blowing increases the loss of metal. At an oxygen consumption of up to 10 m 3 /t for 1 hour, the yield of steel decreases slightly (up to 1%). Oxygen is becoming more and more widespread in open-hearth production. So, if in 1965 with the use of oxygen in open-hearth furnaces 52.1% of steel was smelted, then in 1970 it was already 71%.

Experiments on the use of oxygen in electric steel-smelting furnaces in the USSR began in 1946 at the Elektrostal plant. The introduction of oxygen blast made it possible to increase the productivity of furnaces by 25-30%, to reduce specific consumption electricity by 20-30%, improve the quality of steel, reduce the consumption of electrodes and some scarce alloying additives. The supply of oxygen to electric furnaces proved to be especially effective in the production of stainless steels with a low carbon content, the smelting of which is very difficult due to the carburizing effect of the electrodes. The share of electric steel produced in the USSR using oxygen grew continuously and in 1970 amounted to 74.6% of the total steel production.

In cupola melting, oxygen-enriched blast is mainly used for high overheating of cast iron, which is necessary in the production of high-quality, in particular high-alloy, castings (silicon, chromium, etc.). Depending on the degree of oxygen enrichment of the cupola blast, fuel consumption is reduced by 30-50%, the sulfur content in the metal is reduced by 30-40%, the productivity of the cupola is increased by 80-100%, and the temperature of cast iron produced from it increases significantly (up to 1500 ° C). .

Oxygen in non-ferrous metallurgy became widespread somewhat later than in ferrous metallurgy. Oxygen-enriched blast is used in the converting of matte, in the processes of slag sublimation, walezation, agglomeration, and in the reflective melting of copper concentrates. In the lead, copper and nickel industries, oxygen blast intensified the processes of mine smelting, made it possible to reduce coke consumption by 10-20%, increase penetration by 15-20% and reduce the amount of fluxes in some cases by 2-3 times. Oxygen enrichment of the air blast up to 30% during the roasting of zinc sulfide concentrates increased the productivity of the process by 70% and reduced the volume of exhaust gases by 30%.

• Designation - O (Oxygen);
• Latin name - Oxigenium;
• Period - II;
• Group - 16 (VIa);
• Atomic mass - 15.9994;
• Atomic number - 8;
• Radius of an atom = 60 pm;
• Covalent radius = 73 pm;
• Electron distribution - 1s 2 2s 2 2p 4 ;
• t melting = -218.4°C;
• boiling point = -182.96°C;
• Electronegativity (according to Pauling / according to Alpred and Rochov) = 3.44 / 3.50;
• Oxidation state: +2; +1; 12 ; 0; - thirteen ; - 12 ; -one; -2;
• Density (n.a.) \u003d 1.42897 g / cm 3;
• Molar volume = 14.0 cm 3 / mol.

Oxygen ("generating acids") was discovered in 1774 by J. Priestley. This is the most common chemical element on Earth - the mass fraction of oxygen in the earth's crust is 47.2%. In the atmospheric air, the proportion of oxygen is 21%, which is associated with the activity of green plants.

Oxygen is a constituent of many, both inorganic and organic compounds. Oxygen is necessary for the life of all highly organized living organisms: humans, animals, birds, fish. Oxygen makes up from 50 to 85% of the mass of animal and plant tissues.

Three stable isotopes of oxygen are known: 16 O, 17 O, 18 O.

In the free state, oxygen exists in two allotropic modifications: O 2 - oxygen; O 3 - ozone.

Periodic table of chemical elements of D. I. Mendeleev, stands at number "8", refers to the 16 (VIa) group (See Atoms of the 16 (VIa) group).

Rice. The structure of the oxygen atom.

The oxygen atom contains 8 electrons: 2 electrons are in the inner s-orbital and 6 more in the outer energy level- 2 (paired) on the s-sublevel and 4 (two paired and two unpaired) on the p-sublevel (see Electronic structure of atoms).

Due to the two unpaired p-electrons of the outer level, oxygen forms two covalent bonds, accepting two electrons and showing the oxidation state -2 (H 2 O, CaO, H 2 SO 4).

In compounds with oxygen bonds O-O atom oxygen exhibits an oxidation state of -1 (H 2 O 2).

With the more electronegative fluorine, oxygen donates its valence electrons, exhibiting an oxidation state of +2 (OF 2).

O2

A diatomic oxygen molecule is formed by a double bond of two oxygen atoms. For this reason, molecular oxygen under normal conditions is a stable compound.

The dissociation energy of an oxygen molecule is about 2 times lower than in a nitrogen molecule (see Covalent bond multiplicity), therefore, oxygen has a higher reactivity than nitrogen (but much less than, for example, fluorine).

The reactivity of oxygen increases as it is heated. Oxygen reacts with all elements except inert gases. Due to its high electronegativity (see What is electronegativity) in chemical compounds (with the exception of fluorine), oxygen acts as an oxidizing agent with a degree of -2 (only fluorine oxidizes oxygen to form oxygen difluoride OF 2).

Properties of oxygen gas:

• colorless, odorless and tasteless gas;
• in liquid or solid form, oxygen has a blue color;
• sparingly soluble in water: the mass fraction of oxygen at 20°C is 0.004%.

Chemical properties of oxygen

In all reactions, oxygen plays the role of an oxidizing agent, combining with all elements (with the exception of helium, argon and neon) by direct interaction (except for fluorine, chlorine, gold and platinum metals).

With metals and non-metals simple substances) oxygen forms oxides:

2Cu + O 2 = 2CuO 4Li + O 2 = 2Li 2 O 2Ca + O 2 = 2CaO S + O 2 = SO 2 C + O 2 = CO 2

When the alkali metals sodium and potassium are oxidized, peroxides are formed:

2Na + O 2 \u003d Na 2 O 2

Almost all reactions involving oxygen are exothermic, but there are exceptions:

N 2 + O 2 ↔ 2NO-Q

Many substances react with oxygen to release heat and light, a process called burning.

Combustion reactions:

• combustion of ammonia in air with the formation of water and nitrogen: 4NH 3 + 3O 2 \u003d 2N 2 + 6H 2 O
• catalytic oxidation of ammonia: 4NH 3 + 5O 2 \u003d 2NO + 6H 2 O
• combustion of hydrogen sulfide in excess oxygen: 2H 2 S + 3O 2 \u003d 2SO 2 + 2H 2 O
• with a lack of oxygen, hydrogen sulfide is slowly oxidized to free sulfur: 2H 2 S + O 2 \u003d 2S + 2H 2 O
• combustion of organic substances in oxygen to form water and carbon dioxide: CH 4 + 2O 2 → CO 2 + 2H 2 O C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O
• during the combustion of nitrogen-containing organic substances, in addition to carbon dioxide and water, free nitrogen is released: 4CH 3 NH 5 + 9O 2 → 4CO 2 + 2N 2 + 10H 2 O

Many substances (alcohols, aldehydes, acids) are obtained by the reaction of controlled oxidation of organic substances. Also, many natural processes, such as respiration or decay, are inherently oxidative reactions of organic substances.

An even stronger oxidizing agent than oxygen is ozone, which can oxidize potassium iodide to a free ion - this reaction is used for the qualitative and quantitative determination of ozone: O 3 + 2KI + H 2 O \u003d I 2 ↓ + 2KOH + O 2

Obtaining and using oxygen

Oxygen is widely used in industry and medicine:

• in metallurgy, oxygen is used in the smelting of steel (cast iron);
• in the chemical industry, oxygen is needed for the production of acids (sulfuric and nitric), methanol, acetylene, aldehydes;
• v space industry oxygen is used as an oxidizer for rocket fuel;
• in medicine, oxygen is used in breathing apparatus;
• in nature, oxygen plays an extremely important role - in the process of oxidation of carbohydrates, fats and proteins, the energy necessary for living organisms is released.

Methods of obtaining oxygen:

• industrial ways:
  • liquefaction of air with subsequent separation of the liquid mixture of gases into components;
  • water electrolysis:
    2H 2 O \u003d 2H 2 + O 2.
• laboratory methods (decomposition of salts when heated):
  • potassium permanganate:
    2KMnO 4 \u003d K 2 MnO 4 + MnO 2 + O 2;
  • Berthollet salt:
    2KClO 3 \u003d 2KCl + 3O 2.
• thermal decomposition of alkali metal nitrates:
  2NaNO 3 \u003d 2NaNO 2 + O 2
• catalytic decomposition of hydrogen peroxide (MnO 2 catalyst):
  2H 2 O 2 \u003d 2H 2 O + O 2;
• interaction of carbon dioxide peroxides with alkali metal peroxides:
  2CO 2 + 2Na 2 O 2 \u003d 2Na 2 CO 3 + O 2.