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OXYGEN, O (oxygenium), a chemical element of the VIA subgroup of the periodic table of elements: O, S, Se, Te, Po - a member of the chalcogen family. This is the most common element in nature, its content in the Earth's atmosphere is 21% (vol.), In the earth's crust in the form of compounds approx. 50% (wt.) And in the hydrosphere 88.8% (wt.).

Oxygen is essential for life on earth: animals and plants consume oxygen during respiration, and plants release oxygen during photosynthesis. Living matter contains bound oxygen not only in the composition of body fluids (in blood cells, etc.), but also in the composition of carbohydrates (sugar, cellulose, starch, glycogen), fats and proteins. Clays and rocks are composed of silicates and other oxygen-containing inorganic compounds such as oxides, hydroxides, carbonates, sulfates and nitrates.

Historical reference.

The first information about oxygen became known in Europe from Chinese manuscripts of the 8th century. At the beginning of the 16th century. Leonardo da Vinci published data related to the chemistry of oxygen, not yet knowing that oxygen is an element. Oxygen addition reactions are described in the scientific works of S. Geils (1731) and P. Bayenne (1774). Deserve special attention K. Scheele's research in 1771–1773 on the interaction of metals and phosphorus with oxygen. J. Priestley reported the discovery of oxygen as an element in 1774, several months after Bayen's report on reactions with air. The name oxygenium (oxygen) was given to this element shortly after Priestley's discovery, and is derived from the Greek words for acid-producing; this is due to the misconception that oxygen is present in all acids. The explanation of the role of oxygen in the processes of respiration and combustion, however, belongs to A. Lavoisier (1777).

The structure of the atom.

Any natural oxygen atom contains 8 protons in its nucleus, but the number of neutrons can be 8, 9 or 10. The most common of the three oxygen isotopes (99.76%) is 16 8 O (8 protons and 8 neutrons). The content of another isotope, 18 8 O (8 protons and 10 neutrons), is only 0.2%. This isotope is used as a label or to identify certain molecules, as well as for biochemical and medico-chemical research (a method for studying non-radioactive traces). The third non-radioactive isotope of oxygen 17 8 O (0.04%) contains 9 neutrons and has a mass number of 17. After in 1961 the mass of the carbon isotope 12 6 C was adopted by the International Commission as the standard atomic mass, the weighted average atomic mass of oxygen became 15.9994. Until 1961, chemists considered the standard unit of atomic mass to be the atomic mass of oxygen, taken for a mixture of three natural oxygen isotopes equal to 16,000. Physicists took the mass number of the oxygen isotope 16 8 O as the standard unit of atomic mass, therefore, on the physical scale, the average atomic mass of oxygen was 16.0044.

There are 8 electrons in the oxygen atom, with 2 electrons on the inner level, and 6 electrons on the outer. Therefore, in chemical reactions, oxygen can accept up to two electrons from donors, completing its outer shell up to 8 electrons and forming an excess negative charge.

Molecular oxygen.

Like most other elements, whose atoms lack 1–2 electrons to complete the outer shell of 8 electrons, oxygen forms a diatomic molecule. In this process, a lot of energy is released (~ 490 kJ / mol) and, accordingly, the same amount of energy must be spent for the reverse process of dissociation of a molecule into atoms. The O – O bond is so strong that at 2300 ° C only 1% of oxygen molecules dissociate into atoms. (It is noteworthy that when the nitrogen molecule N 2 is formed, the strength of the N – N bond is even higher, ~ 710 kJ / mol.)

Electronic structure.

In the electronic structure of the oxygen molecule, as one might expect, the distribution of electrons by the octet around each atom is not realized, but there are unpaired electrons, and oxygen exhibits properties typical of such a structure (for example, interacts with magnetic field, being a paramagnet).

Reactions.

Under appropriate conditions, molecular oxygen reacts with almost any element other than noble gases. However, under room conditions, only the most active elements react with oxygen rather quickly. Probably, most of the reactions proceed only after the dissociation of oxygen into atoms, and dissociation occurs only at very high temperatures. However, catalysts or other substances in the reacting system can promote the dissociation of O 2. It is known that alkaline (Li, Na, K) and alkaline earth (Ca, Sr, Ba) metals react with molecular oxygen to form peroxides:

Receiving and applying.

Due to the presence of free oxygen in the atmosphere, the most effective method for extracting it is air liquefaction, from which impurities, CO 2, dust, etc. are removed. chemical and physical methods. The cyclical process includes compression, cooling and expansion, which leads to the liquefaction of air. With a slow rise in temperature (fractional distillation method), noble gases (the most difficult to liquefy) evaporate from liquid air, then nitrogen and liquid oxygen remains. As a result, liquid oxygen contains traces of noble gases and a relatively large percentage of nitrogen. For many applications, these impurities do not interfere. However, to obtain oxygen of high purity, the distillation process must be repeated. Oxygen is stored in tanks and cylinders. It is used in large quantities as an oxidizing agent for kerosene and other fuels in rockets and spacecraft. The steel industry consumes oxygen gas to be blown through the molten iron according to the Bessemer method for quick and effective removal impurities C, S and P. Steel with oxygen blast is obtained faster and of better quality than with air. Oxygen is also used for welding and cutting metals (oxygen-acetylene flame). Oxygen is also used in medicine, for example, to enrich the respiratory environment of patients with shortness of breath. Oxygen can be obtained by various chemical methods, and some of them are used to obtain small amounts of pure oxygen in laboratory practice.

Electrolysis.

One of the methods for producing oxygen is electrolysis of water containing small additions of NaOH or H 2 SO 4 as a catalyst: 2H 2 O ® 2H 2 + O 2. In this case, small impurities of hydrogen are formed. With the help of a discharge device, traces of hydrogen in the gas mixture are again converted into water, the vapors of which are removed by freezing or adsorption.

Thermal dissociation.

An important laboratory method for producing oxygen, proposed by J. Priestley, is the thermal decomposition of heavy metal oxides: 2HgO ® 2Hg + O 2. Priestley focused the sun's rays onto mercury oxide powder for this. A well-known laboratory method is also the thermal dissociation of oxosalts, for example potassium chlorate in the presence of a catalyst - manganese dioxide:

Manganese dioxide, added in small amounts before calcining, allows maintaining the required temperature and dissociation rate, and MnO 2 itself does not change in the process.

Methods of thermal decomposition of nitrates are also used:

as well as peroxides of some active metals, for example:

2BaO 2 ® 2BaO + O 2

The latter method was at one time widely used to extract oxygen from the atmosphere and consisted of heating BaO in air to form BaO 2, followed by thermal decomposition of peroxide. The thermal decomposition process remains important for the production of hydrogen peroxide.

SOME PHYSICAL PROPERTIES OF OXYGEN
Atomic number	8
Atomic mass	15,9994
Melting point, ° С	–218,4
Boiling point, ° С	–183,0
Density
solid, g / cm 3 (at t pl)	1,27
liquid g / cm 3 (at t bale)	1,14
gaseous, g / dm 3 (at 0 ° С)	1,429
relative to air	1,105
critical a, g / cm 3	0,430
Critical temperature a, ° С	–118,8
Critical pressure a, atm	49,7
Solubility, cm 3/100 ml solvent
in water (0 ° C)	4,89
in water (100 ° C)	1,7
in alcohol (25 ° C)	2,78
Radius, Å	0,74
covalent	0,66
ionic (О 2–)	1,40
Ionization potential, V
first	13,614
second	35,146
Electronegativity (F = 4)	3,5
a Temperature and pressure at which the densities of gas and liquid are the same.

Physical properties.

Oxygen under normal conditions is a colorless, odorless and tasteless gas. Liquid oxygen is pale blue in color. Solid oxygen exists in at least three crystalline modifications. Oxygen gas is soluble in water and is likely to form fragile compounds such as O 2 CH H 2 O, and possibly O 2 CH 2H 2 O.

Chemical properties.

As already mentioned, the reactivity of oxygen is determined by its ability to dissociate into O atoms, which are highly reactive. Only the most reactive metals and minerals react with O 2 at a high rate at low temperatures. The most active alkaline (IA subgroups) and some alkaline earth (IIA subgroups) metals form with O 2 peroxides such as NaO 2 and BaO 2. Other elements and compounds react only with the dissociation product O 2. Under suitable conditions, all elements, excluding noble gases and metals Pt, Ag, Au, react with oxygen. These metals also form oxides, but under special conditions.

The electronic structure of oxygen (1s 2 2s 2 2p 4) is such that the O atom takes two electrons to the outer level to form a stable outer electron shell, forming the O 2– ion. In alkali metal oxides, mainly ionic bond... It can be assumed that the electrons of these metals are almost entirely drawn towards oxygen. In oxides of less active metals and non-metals, the electron transition is incomplete, and the negative charge density on oxygen is less pronounced, therefore the bond is less ionic or more covalent.

When metals are oxidized with oxygen, heat is released, the value of which correlates with the strength of the M – O bond. When some non-metals are oxidized, heat is absorbed, which indicates their less strong bonds with oxygen. Such oxides are thermally unstable (or less stable than ionically bonded oxides) and are often highly reactive. For comparison, the table shows the values ​​of the formation enthalpies of oxides of the most typical metals, transition metals and non-metals, elements of the A- and B-subgroups (the minus sign means heat release).

Several general conclusions can be drawn about the properties of oxides:

1. The melting points of alkali metal oxides decrease with increasing atomic radius of the metal; So, t pl (Cs 2 O) t pl (Na 2 O). Oxides in which ionic bond predominates have higher melting points than the melting points of covalent oxides: t pl (Na 2 O)> t pl (SO 2).

2. Oxides of reactive metals (IA – IIIA subgroups) are more thermally stable than oxides of transition metals and non-metals. Heavy metal oxides in the highest oxidation state upon thermal dissociation form oxides with lower oxidation states (for example, 2Hg 2+ O ® (Hg +) 2 O + 0.5O 2 ® 2Hg 0 + O 2). Such oxides in high oxidation states can be good oxidizing agents.

3. The most active metals interact with molecular oxygen at elevated temperatures to form peroxides:

Sr + O 2 ® SrO 2.

4. Oxides of active metals form colorless solutions, while oxides of most transition metals are colored and practically insoluble. Aqueous solutions of metal oxides exhibit basic properties and are hydroxides containing OH groups, while nonmetal oxides in aqueous solutions form acids containing the H + ion.

5. Metals and non-metals of A-subgroups form oxides with an oxidation state corresponding to the group number, for example, Na, Be and B form Na 1 2 O, Be II O and B 2 III O 3, and non-metals IVA – VIIA of subgroups C, N , S, Cl form C IV O 2, NV 2 O 5, S VI O 3, Cl VII 2 O 7. The group number of an element correlates only with the maximum oxidation state, since oxides with lower oxidation states of the elements are also possible. In the combustion processes of compounds, oxides are typical products, for example:

2H 2 S + 3O 2 ® 2SO 2 + 2H 2 O

Carbon-containing substances and hydrocarbons under low heating are oxidized (burned) to CO 2 and H 2 O. Examples of such substances are fuels - wood, oil, alcohols (as well as carbon - coal, coke and charcoal). The heat from the combustion process is utilized for the production of steam (and then electricity or goes to power plants), as well as for heating houses. Typical equations for combustion processes are:

a) wood (cellulose):

(C 6 H 10 O 5) n + 6n O 2 ® 6 n CO 2 + 5 n H 2 O + heat energy

b) oil or gas (gasoline C 8 H 18 or natural gas CH 4):

2C 8 H 18 + 25O 2 ® 16CO 2 + 18H 2 O + thermal energy

CH 4 + 2O 2 ® CO 2 + 2H 2 O + thermal energy

C 2 H 5 OH + 3O 2 ® 2CO 2 + 3H 2 O + thermal energy

d) carbon (coal or charcoal, coke):

2C + O 2 ® 2CO + thermal energy

2CO + O 2 ® 2CO 2 + thermal energy

A number of C-, H-, N-, O-containing compounds with a high energy reserve are also subject to combustion. Oxygen for oxidation can be used not only from the atmosphere (as in previous reactions), but also from the substance itself. A slight activation of the reaction, such as a shock or shock, is sufficient to initiate a reaction. In these reactions, oxides are also combustion products, but they are all gaseous and expand rapidly at a high final process temperature. Therefore, such substances are explosive. Examples of explosives are trinitroglycerin (or nitroglycerin) C 3 H 5 (NO 3) 3 and trinitrotoluene (or TNT) C 7 H 5 (NO 2) 3.

Metal or non-metal oxides with lower degrees oxidation of the element react with oxygen to form oxides high degrees oxidation of this element:

Natural oxides, obtained from ores or synthesized, serve as raw materials for the production of many important metals, for example, iron from Fe 2 O 3 (hematite) and Fe 3 O 4 (magnetite), aluminum from Al 2 O 3 (alumina), magnesium from MgO (magnesia). Light metal oxides are used in the chemical industry to produce alkalis or bases. Potassium peroxide KO 2 finds unusual use, since in the presence of moisture and as a result of reaction with it, it releases oxygen. Therefore, KO 2 is used in respirators to obtain oxygen. Moisture from exhaled air releases oxygen in the respirator, while KOH absorbs CO 2. Obtaining CaO oxide and calcium hydroxide Ca (OH) 2 - large-scale production in the technology of ceramics and cement.

Water (hydrogen oxide).

The importance of water H 2 O both in laboratory practice for chemical reactions and in vital processes requires special consideration of this substance WATER, ICE AND STEAM). As already mentioned, during the direct interaction of oxygen and hydrogen under conditions, for example, of a spark discharge, an explosion and the formation of water occur, while 143 kJ / (mol H 2 O) are released.

The water molecule has an almost tetrahedral structure, the H – O – H angle is 104 ° 30ў. The bonds in the molecule are partially ionic (30%) and partially covalent with a high density of negative charge for oxygen and, accordingly, positive charges for hydrogen:

Due to the high strength of the H – O bonds, hydrogen is hardly split off from oxygen, and water exhibits very weak acidic properties. Many properties of water are determined by the distribution of charges. For example, a water molecule forms a hydrate with a metal ion:

Water gives one electron pair to an acceptor, which can be H +:

Oxoanions and oxocations

- oxygen-containing particles with a residual negative (oxoanions) or residual positive (oxocations) charge. The O 2– ion has a high affinity (high reactivity) for positively charged particles of the H + type. The simplest representative of stable oxoanions is the hydroxide ion OH -. This explains the instability of atoms with a high charge density and their partial stabilization as a result of the attachment of a particle with a positive charge. Therefore, under the action of an active metal (or its oxide) on water, OH - is formed, and not O 2–:

2Na + 2H 2 O ® 2Na + + 2OH - + H 2

Na 2 O + H 2 O ® 2Na + + 2OH -

More complex oxoanions are formed from oxygen with a metal ion or a non-metallic particle with a large positive charge, resulting in a low-charged particle with greater stability, for example:

° C a dark purple solid phase is formed. Liquid ozone is poorly soluble in liquid oxygen, and 49 cm 3 O 3 dissolves in 100 g of water at 0 ° C. In terms of chemical properties, ozone is much more active than oxygen and in terms of oxidizing properties it is second only to O, F 2 and OF 2 (oxygen difluoride). Normal oxidation produces oxide and molecular oxygen O 2. Under the action of ozone on active metals under special conditions, ozonides of the composition K + O 3 - are formed. Ozone is obtained in industry for special purposes, it is good disinfectant and is used for water purification and as a bleach, improves the state of the atmosphere in closed systems, disinfects objects and food, accelerates the ripening of grains and fruits. In a chemical laboratory, an ozonizer is often used to produce ozone, which is required for some methods. chemical analysis and synthesis. Rubber is easily degraded even by low ozone concentrations. In some industrial cities, significant concentrations of ozone in the air lead to rapid deterioration of rubber products if they are not protected by antioxidants. Ozone is highly toxic. Continuous inhalation of air, even with very low ozone concentrations, causes headaches, nausea and other unpleasant conditions.

One of essential elements there is oxygen on our planet. The chemical properties of this substance allow it to participate in biological processes, and the increased activity makes oxygen a significant participant in all known chemical reactions. In a free state, this substance is present in the atmosphere. In a bound state, oxygen is part of minerals, rocks, complex substances that make up various living organisms. The total amount of oxygen on Earth is estimated at 47% of the total mass of our planet.

Oxygen designation

In the periodic table, oxygen occupies the eighth cell of this table. Its international name is oxigenium. In chemical records, it is designated by the Latin letter "O". Atomic oxygen does not occur in the natural environment, its particles combine to form paired gas molecules, the molecular weight of which is 32 g / mol.

Air and oxygen

Air is a mixture of several gases common on Earth. Most of all in the air mass of nitrogen - 78.2% by volume and 75.5% by mass. Oxygen takes only the second place in terms of volume - 20.9%, and by weight - 23.2%. The third place is reserved for noble gases. The rest of the impurities - carbon dioxide, water vapor, dust, etc. - occupy only a fraction of a percent in the total air mass.

The entire mass of natural oxygen is a mixture of three isotopes - 16 O, 17 O, 18 O. The percentage of these isotopes in the total mass of oxygen is 99.76%, 0.04% and 0.2%, respectively.

Physical and chemical properties of oxygen

One liter of air under normal conditions weighs 1.293 g. When the temperature drops to -140⁰C, the air becomes a colorless transparent liquid. In spite of low temperature boiling air can be kept in liquid state even at room temperature. For this, the liquid must be placed in a so-called Dewar vessel. Immersion in liquid oxygen radically changes the normal properties of objects.

Ethyl alcohol and many gases become solid objects, mercury becomes hard and malleable, and a rubber ball loses its elasticity and crumbles at the slightest impact.

Oxygen dissolves in water, albeit in small quantities - seawater contains 3-5% oxygen. But even such a small amount of this gas gave rise to the existence of fish, molluscs and various marine organisms that receive oxygen from the water to support their own life support processes.

The structure of the oxygen atom

The described properties of oxygen are primarily explained by the internal structure of this element.

Oxygen belongs to the main subgroup of the sixth group of elements of the periodic table. In the outer electron cloud of the element, there are six electrons, four of which occupy p-orbitals, and the remaining two are located in s-orbitals. Such an internal structure causes high energy costs aimed at breaking electronic communications- it is easier for the oxygen atom to borrow two missing electrons to the outer orbital than to give up its own six. Therefore, the covalence of oxygen in most cases is equal to two. Owing to two free electrons, oxygen easily forms diatomic molecules, which are characterized by a high bond strength. Only when the applied energy exceeds 498 J / mol, the molecules disintegrate and atomic oxygen is formed. The chemical properties of this element allow it to react with all known substances, excluding helium, neon and argon. The rate of interaction depends on the reaction temperature and on the nature of the substance.

Chemical properties of oxygen

With various substances, oxygen enters into reactions of formation of oxides, and these reactions are characteristic of both metals and non-metals. Oxygen compounds with metals are called basic oxides - classic example serves as magnesium oxide and calcium oxide. The interaction of metal oxides with water leads to the formation of hydroxides, which confirm the active chemical properties of oxygen. With non-metals, this substance forms acid oxides- for example, sulfur trioxide SO 3. When this element interacts with water, sulfuric acid is obtained.

Chemical activity

Oxygen interacts directly with the overwhelming majority of elements. The exceptions are gold, halogens and platinum. The interaction of oxygen with some substances is greatly accelerated in the presence of catalysts. For example, a mixture of hydrogen and oxygen in the presence of platinum reacts even at room temperature. With a deafening explosion, the mixture turns into ordinary water, an important part of which is oxygen. The chemical properties and high activity of the element explain the release of a large amount of light and heat, therefore chemical reactions with oxygen is often called combustion.

Combustion in pure oxygen is much more intense than in air, although the amount of heat released during the reaction will be approximately the same, but the process, due to the absence of nitrogen, proceeds much faster, and the combustion temperature becomes higher.

Oxygen production

In 1774, the English scientist D. Priestley isolated an unknown gas from the decomposition of mercury oxide. But the scientist did not associate the emitted gas with the already known substance that is part of the air. Only a few years later, the great Lavoisier studied physicochemical properties oxygen obtained in this reaction, and proved its identity with the gas that is part of the air. In the modern world, oxygen is obtained from the air. In laboratories I use industrial oxygen, which is supplied in cylinders under a pressure of about 15 MPa. Pure oxygen can also be obtained in laboratory conditions; the standard method for its production is thermal decomposition of potassium permanganate, which proceeds according to the formula:

Ozone production

If electricity is passed through oxygen or air, then a characteristic smell will appear in the atmosphere, foreshadowing the appearance of a new substance - ozone. Ozone can also be obtained from chemically pure oxygen. The formation of this substance can be expressed by the formula:

This reaction cannot proceed on its own - external energy is required for its successful completion. But the reverse transformation of ozone into oxygen occurs spontaneously. The chemical properties of oxygen and ozone differ in many ways. Ozone differs from oxygen in density, melting point and boiling point. Under normal conditions, this gas is blue in color and has a characteristic odor. Ozone has a higher electrical conductivity and is more soluble in water than oxygen. The chemical properties of ozone are explained by the process of its decay - when the molecule of this substance decomposes, a diatomic oxygen molecule is formed plus one free atom of this element, which reacts aggressively with other substances. For example, the reaction between ozone and oxygen is known: 6Ag + O 3 = 3Ag 2 O

But ordinary oxygen does not combine with silver even at high temperatures.

In nature, the active decomposition of ozone is fraught with the formation of so-called ozone holes, which endanger the life processes on our planet.

Oxygen formsperoxides with the oxidation state -1.
- For example, peroxides are produced by the combustion of alkali metals in oxygen:
2Na + O 2 → Na 2 O 2

- Some oxides absorb oxygen:
2BaO + O 2 → 2BaO 2

- According to the principles of combustion, developed by A. N. Bach and K. O. Engler, oxidation occurs in two stages with the formation of an intermediate peroxide compound. This intermediate compound can be isolated, for example, when the flame of burning hydrogen is cooled with ice, along with water, hydrogen peroxide is formed:
H 2 + O 2 → H 2 O 2

Superoxides have an oxidation state of -1/2, that is, one electron per two oxygen atoms (O 2 - ion). Obtained by the interaction of peroxides with oxygen at high pressures and temperature:
Na 2 O 2 + O 2 → 2NaO 2

Ozonides contain ion O 3 - with the oxidation state -1/3. Obtained by the action of ozone on alkali metal hydroxides:
KOH (TV) + O 3 → KOH 3 + KOH + O 2

And he dioxygenyl O 2 + has an oxidation state of +1/2. Received by the reaction:
PtF 6 + O 2 → O 2 PtF 6

Oxygen fluorides
Oxygen difluoride, OF 2 oxidation state +2, is obtained by passing fluorine through an alkali solution:
2F 2 + 2NaOH → OF 2 + 2NaF + H 2 O

Oxygen monofluoride (Dioxyfluoride), O 2 F 2, unstable, oxidation state +1. It is obtained from a mixture of fluorine and oxygen in a glow discharge at a temperature of -196 ° C.

Passing a glow discharge through a mixture of fluorine with oxygen at a certain pressure and temperature, mixtures of higher oxygen fluorides O 3 F 2, O 4 F 2, O 5 F 2 and O 6 F 2 are obtained.
Oxygen supports the processes of respiration, combustion, and decay. In free form, the element exists in two allotropic modifications: O 2 and O 3 (ozone).

Oxygen application

The widespread industrial use of oxygen began in the middle of the 20th century, after the invention of turbo expanders - devices for liquefying and separating liquid air.

In metallurgy

The converter method of steel production is associated with the use of oxygen.

Welding and cutting metals

Oxygen in cylinders is widely used for flame cutting and welding of metals.

Rocket fuel

Liquid oxygen, hydrogen peroxide, is used as an oxidizing agent for rocket fuel. Nitric acid and other oxygen-rich compounds. A mixture of liquid oxygen and liquid ozone is one of the most powerful oxidizing agents in rocket fuel (the specific impulse of the hydrogen - ozone mixture exceeds the specific impulse for the hydrogen-fluorine and hydrogen-oxygen fluoride pair).

In medicine

Oxygen is used to enrich breathing gas mixtures in case of respiratory failure, for the treatment of asthma, in the form of oxygen cocktails, oxygen bags, etc.

In the food industry

V Food Industry oxygen is registered as a food additive E948 as a propellant and packing gas.

The biological role of oxygen

Living things breathe oxygen in the air. Oxygen is widely used in medicine. In case of cardiovascular diseases, oxygen foam ("oxygen cocktail") is introduced into the stomach to improve metabolic processes. Subcutaneous oxygen administration is used for trophic ulcers, elephantiasis, gangrene and others. serious illnesses... For disinfection and deodorization of air and cleaning drinking water artificial enrichment with ozone is used. The radioactive isotope of oxygen 15 O is used for studies of blood flow velocity and pulmonary ventilation.

Toxic oxygen derivatives

Some oxygen derivatives (so-called reactive oxygen species) such as singlet oxygen, hydrogen peroxide, superoxide, ozone and hydroxyl radicals are highly toxic products. They are formed during the activation or partial reduction of oxygen. Superoxide (superoxide radical), hydrogen peroxide and hydroxyl radical can form in the cells and tissues of the human and animal body and cause oxidative stress.

Oxygen isotopes

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 number of oxygen atoms on Earth. The sharp predominance of the isotopes of the lightest of them 16 O in the mixture 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 structure of the atomic nucleus, are especially stable.

There are radioactive isotopes 11 O, 13 O, 14 O (half-life 74 sec), 15 O (T 1/2 = 2.1 min), 19 O (T 1/2 = 29.4 sec), 20 O (contradictory half-life data from 10 min to 150 years).

Additional Information

Oxygen compounds
Liquid oxygen
Ozone

Oxygen, Oxygenium, O (8)
The discovery of oxygen (Oxygen, French Oxygene, German Sauerstoff) marked the beginning of the modern period in the development of chemistry. It has been known since ancient times that air is needed for combustion, but for many centuries the combustion process remained incomprehensible. Only in the 17th century. Mayow and Boyle independently expressed the idea that the air contains some substance that supports combustion, but this completely rational hypothesis was not developed then, since the idea of ​​combustion as a process of combining a burning body with a certain constituent part of the air seemed at that time, contrary to such an obvious act as the fact that during combustion there is a decomposition of a burning body into elementary components. It was on this basis that at the turn of the 17th century. the theory of phlogiston, created by Becher and Stahl, arose. With the onset of the chemical-analytical period of the development of chemistry (the second half of the 18th century) and the emergence of "pneumatic chemistry" - one of the main branches of the chemical-analytical direction - combustion and respiration again attracted the attention of researchers. Discovery of various gases and the establishment of them important role in chemical processes was one of the main incentives for systematic studies of combustion processes of substances undertaken by Lavoisier. Oxygen was discovered in the early 70s of the 18th century.

The first report of this discovery was made by Priestley at a meeting of the English Royal Society in 1775. Priestley, heating red mercury oxide with a large incendiary glass, obtained a gas in which a candle burned more brightly than in ordinary air, and a smoldering torch flared. Priestley identified some of the properties of the new gas and called it daphlogisticated air. However, two years earlier Priestley (1772) Scheele also received oxygen by decomposition of mercury oxide and in other ways. Scheele called this gas Feuerluft. Scheele was able to report his discovery only in 1777.

In 1775, Lavoisier appeared before the Paris Academy of Sciences with the message that he had succeeded in obtaining "the cleanest part of the air that surrounds us," and described the properties of this part of the air. At the beginning, Lavoisier called this "air" the empirical, vital (Air empireal, Air vital) base of the vital air (Base de l "air vital). The almost simultaneous discovery of oxygen by several scientists in different countries sparked disputes over priority. Priestley was especially persistent in his pursuit of recognition as a pioneer. In essence, these disputes have not ended until now. A detailed study of the properties of oxygen and its role in combustion and the formation of oxides led Lavoisier to the wrong conclusion that this gas is an acid-forming principle. In 1779, in accordance with this conclusion, Lavoisier introduced a new name for oxygen - the acid-forming principle (principe acidifiant ou principe oxygine). The word oxygine appearing in this complex name Lavoisier derived from the Greek - acid and "I produce."

Oxygen O has atomic number 8, located in the main subgroup (subgroup a) VI group, in the second period. In oxygen atoms, valence electrons are located on the 2nd energy level having only s- and p-orbital. This excludes the possibility of transition of O atoms to an excited state, therefore, oxygen in all compounds exhibits a constant valence equal to II. Having a high electronegativity, oxygen atoms are always negatively charged in compounds (s.r. = -2 or -1). The exception is fluorides OF 2 and O 2 F 2.

For oxygen, the oxidation states are -2, -1, +1, +2

General characteristics of the element

Oxygen is the most abundant element on Earth, accounting for slightly less than half, 49% of the total mass of the earth's crust. Natural oxygen consists of 3 stable isotopes 16 O, 17 O and 18 O (16 O prevails). Oxygen is part of the atmosphere (20.9% by volume, 23.2% by mass), water and more than 1400 minerals: silica, silicates and aluminosilicates, marbles, basalts, hematite and other minerals and rocks. Oxygen makes up 50-85% of the mass of tissues of plants and animals, because it is contained in proteins, fats and carbohydrates that make up living organisms. The role of oxygen for respiration and for oxidation processes is well known.

Oxygen is relatively slightly soluble in water - 5 volumes in 100 volumes of water. However, if all the oxygen dissolved in water passed into the atmosphere, then it would occupy a huge volume - 10 million km 3 (n.u). This is equal to about 1% of all oxygen in the atmosphere. The formation of an oxygen atmosphere on earth is due to the processes of photosynthesis.

Discovered by the Swede K. Scheele (1771 - 1772) and the Englishman J. Priestley (1774). The first used heating of nitrate, the second - mercury oxide (+2). The name was given by A. Lavoisier ("oxygenium" - "giving birth to acids").

In free form, it exists in two allotropic modifications - "ordinary" oxygen O 2 and ozone O 3.

Ozone molecule structure

3O 2 = 2O 3 - 285 kJ
Ozone in the stratosphere forms a thin layer that absorbs most of the biologically harmful ultraviolet radiation.
During storage, ozone spontaneously converts to oxygen. Oxygen O 2 is chemically less active than ozone. The electronegativity of oxygen is 3.5.

Physical properties of oxygen

O 2 - gas without color, odor and taste, so pl. –218.7 ° С, b.p. –182.96 ° C, paramagnetic.

Liquid O 2 blue, solid - of blue color... O 2 is soluble in water (better than nitrogen and hydrogen).

Oxygen production

1. Industrial method - liquid air distillation and water electrolysis:

2H 2 O → 2H 2 + O 2

2. In the laboratory, oxygen is obtained:
1.Electrolysis of alkaline aqueous solutions or aqueous solutions of oxygen-containing salts (Na 2 SO 4, etc.)

2. Thermal decomposition of potassium permanganate KMnO 4:
2KMnO 4 = K 2 MnO4 + MnO 2 + O 2,

Berthollet's salt KClO 3:
2KClO 3 = 2KCl + 3O 2 (catalyst MnO 2)

Manganese oxide (+4) MnO 2:
4MnO 2 = 2Mn 2 O 3 + O 2 (700 o C),

3MnO 2 = 2Mn 3 O 4 + O 2 (1000 o C),

Barium peroxide BaO 2:
2BaO 2 = 2BaO + O 2

3. By decomposition of hydrogen peroxide:
2H 2 O 2 = H 2 O + O 2 (catalyst MnO 2)

4. Decomposition of nitrates:
2KNO 3 → 2KNO 2 + O 2

On spaceships and submarines, oxygen is obtained from a mixture of K 2 O 2 and K 2 O 4:
2K 2 O 4 + 2H 2 O = 4KOH + 3O 2
4KOH + 2CO 2 = 2K 2 CO 3 + 2H 2 O

In total:
2K 2 O 4 + 2CO 2 = 2K 2 CO 3 + 3О 2

When using K 2 O 2, the overall reaction looks like this:
2K 2 O 2 + 2CO 2 = 2K 2 CO 3 + O 2

If you mix K 2 O 2 and K 2 O 4 in equal molar (ie equimolar) amounts, then one mole of O 2 will be released per 1 mole of absorbed CO 2.

Chemical properties of oxygen

Oxygen supports combustion. Combustion - b A rapid oxidation process of a substance, accompanied by the release of a large amount of heat and light. To prove that the bottle contains oxygen, and not some other gas, a smoldering splinter must be dipped into the bottle. In oxygen, a smoldering splinter flares up brightly. Combustion of various substances in air is a redox process in which oxygen is the oxidizing agent. Oxidants are substances that "take" electrons from reducing substances. The good oxidizing properties of oxygen can be easily explained by the structure of its outer electron shell.

The oxygen valence shell is located at the 2nd level - relatively close to the nucleus. Therefore, the nucleus strongly attracts electrons to itself. On the valence shell of oxygen 2s 2 2p 4 there are 6 electrons. Consequently, two electrons are missing to the octet, which oxygen seeks to take from the electronic shells of other elements, entering into reactions with them as an oxidizing agent.

Oxygen has the second (after fluorine) electronegativity in the Pauling scale. Therefore, in the overwhelming majority of its compounds with other elements, oxygen has negative oxidation state. A stronger oxidant than oxygen is only its neighbor in the period - fluorine. Therefore, oxygen compounds with fluorine are the only ones where oxygen has positive degree oxidation.

So, oxygen is the second most powerful oxidizing agent among all the elements of the Periodic Table. Most of its most important chemical properties are associated with this.
All elements react with oxygen, except for Au, Pt, He, Ne and Ar, in all reactions (except for interaction with fluorine) oxygen is an oxidizing agent.

Oxygen reacts readily with alkali and alkaline earth metals:

4Li + O 2 → 2Li 2 O,

2K + O 2 → K 2 O 2,

2Ca + O 2 → 2CaO,

2Na + O 2 → Na 2 O 2,

2K + 2O 2 → K 2 O 4

Fine iron powder (so-called pyrophoric iron) ignites spontaneously in air, forming Fe 2 O 3, and steel wire burns in oxygen if it is heated in advance:

3 Fe + 2O 2 → Fe 3 O 4

2Mg + O 2 → 2MgO

2Cu + O 2 → 2CuO

Oxygen reacts with non-metals (sulfur, graphite, hydrogen, phosphorus, etc.) when heated:

S + O 2 → SO 2,

C + O 2 → CO 2,

2H 2 + O 2 → H 2 O,

4P + 5O 2 → 2P 2 O 5,

Si + O 2 → SiO 2, etc.

Almost all reactions involving oxygen O 2 are exothermic, with rare exceptions, for example:

N 2 + O 2 → 2NO - Q

This reaction takes place at temperatures above 1200 o C or in an electric discharge.

Oxygen is capable of oxidizing complex substances, for example:

2H 2 S + 3O 2 → 2SO 2 + 2H 2 O (excess oxygen),

2H 2 S + O 2 → 2S + 2H 2 O (lack of oxygen),

4NH 3 + 3O 2 → 2N 2 + 6H 2 O (without catalyst),

4NH 3 + 5O 2 → 4NO + 6H 2 O (in the presence of a Pt catalyst),

CH 4 (methane) + 2O 2 → CO 2 + 2H 2 O,

4FeS 2 (pyrite) + 11O 2 → 2Fe 2 O 3 + 8SO 2.

Known compounds containing the dioxygenyl cation O 2 +, for example, O 2 + - (the successful synthesis of this compound prompted N. Bartlett to try to obtain compounds of inert gases).

Ozone

Ozone is chemically more reactive than oxygen O 2. So, ozone oxidizes iodide - ions I - in a Kl solution:

O 3 + 2Kl + H 2 O = I 2 + O 2 + 2KOH

Ozone is highly toxic, its poisonous properties are stronger than, for example, hydrogen sulfide. However, in nature, ozone contained in the high layers of the atmosphere plays the role of a protector of all life on Earth from the harmful ultraviolet radiation of the sun. A thin ozone layer absorbs this radiation and does not reach the Earth's surface. There are significant fluctuations in the thickness and length of this layer over time (the so-called ozone holes) the reasons for such fluctuations have not yet been clarified.

Oxygen application O 2: to intensify the processes of obtaining iron and steel, when smelting non-ferrous metals, as an oxidizing agent in various chemical industries, for life support on submarines, as an oxidizer for rocket fuel (liquid oxygen), in medicine, when welding and cutting metals.

Ozone O 3 application: for disinfection of drinking water, Wastewater, air, for bleaching fabrics.

Chemistry lesson grade 8

Theme: Oxygen, its general characteristics. Being in nature. Getting oxygen and its physical properties.

The purpose of the lesson: to continue the formation of the concepts "chemical element", "simple substance", "chemical reaction". To form ideas about the methods of obtaining oxygen in the laboratory. Introduce the concept of a catalyst, physical properties, characterize an element according to D.I. Mendeleev. Improve your interactive whiteboard skills.

Basic concepts... Catalysts.

Planned learning outcomes

Subject. To be able to distinguish between the concepts of "chemical element", "simple substance" on the example of oxygen. Be able to characterize the physical properties and methods of oxygen collection.

Metasubject... Develop the ability to work according to plan, formulate, argue, organize educational cooperation and joint activities with teacher and peers.

Personal. To form a responsible attitude towards learning, readiness for self-education.

The main activities of students. Describe a chemical element according to the proposed plan. Describe the chemical reactions observed during the demonstration experiment. Participate in a joint discussion of the results. Draw conclusions from the results of experiments.

Demonstrations... Getting oxygen from hydrogen peroxide.

During the classes

Learning new material.

1. Frontal conversation:

What gas supports breathing and combustion?

What information about oxygen do you already know from courses in natural history, botany?

What substances contain oxygen? (water, sand, rocks, minerals, proteins, fats, carbohydrates).

general characteristics chemical element oxygen:

Chemical sign (O).

Relative atomic mass (16).

Valence (II).

The chemical formula of a simple substance (O2).

Relative molecular weight of a simple substance (32).

Characterize element no. 8, based on its position in the periodic table of chemical elements of D.I. Mendeleev. (serial number - 8, atomic mass - 16, IV - group number, period number - 2).

Being in nature.

Oxygen is the most abundant chemical element in the earth's crust (49%). Air contains 21% oxygen gas. Oxygen is an important part of organic compounds that are of great importance for living organisms.

Physical properties: oxygen is a colorless gas, tasteless and odorless, slightly soluble in water (in 100 volumes of water - 3.1 volumes of oxygen). Oxygen is slightly heavier than air (Мr (О2) = 2х16 = 32, p air = 29).

2. Experiments on obtaining oxygen.

Getting in the laboratory.

For the first time, oxygen gas was obtained in 1774 English. by the scientist Joseph Priestley. Upon calcining the oxide of mercury (II) Priestley received "air":

The scientist decided to investigate the effect of the obtained gas on the candle flame: under the influence of this gas, the candle flame became dazzlingly bright, an iron wire burned out in the stream of the obtained gas. Mice, placed in a vessel with this gas, breathed easily, the scientist himself tried to inhale this gas and noted that it was easy to breathe.

In the school laboratory, we get this gas from hydrogen peroxide. To observe the physical properties of oxygen, we repeat the rules safety precautions.

In a test tube with a solution of hydrogen peroxide, we put a little manganese (IV) oxide MnO2, a violent reaction begins with the release of oxygen. The release of oxygen is confirmed by a smoldering splinter (it flashes and burns). At the end of the reaction, manganese (IV) oxide settles to the bottom, it can be used again. Consequently, manganese (IV) oxide accelerates the decomposition reaction of hydrogen peroxide, but is not consumed in this case.

Definition:

Substances that accelerate chemical reactions, but are not consumed themselves and are not part of the reaction products, are called catalysts.

2Н2О2 MnO2 2Н2О + О2

In the school laboratory, oxygen is obtained in another way:

By heating potassium permanganate

2КМnO4 = К2MnO4 + MnO2 + О2

Manganese (IV) oxide accelerates another reaction for producing oxygen - the decomposition reaction when heated potassium chlorate KClO3 (Berthollet's salt): 2KSlO3 MnO2 2KSl + 3O2

3. Working with the textbook:

US. 75 read about industrial applications of catalysts.

In fig. 25 and fig. 26 shows methods for collecting oxygen. What physical properties are known to you based on the methods of collecting oxygen by the method of air displacement? (oxygen is heavier than air: 32 29), by displacing water? (oxygen is slightly soluble in water). How to properly assemble a displacement oxygen scavenger? (Fig. 25) Answer: The oxygen collection tube should be positioned bottom down. How can you detect or prove the presence of oxygen in a vessel? (by the flashing of a smoldering splinter).

with. 75 read the textbook article "Getting in the Industry." What physical property of oxygen is such a method of obtaining it based on? (Liquid oxygen has a boiling point higher than liquid nitrogen, so the nitrogen will evaporate and the oxygen will remain).

II.Consolidation of knowledge, skills.

What substances are called catalysts?

with. 76 test items.

Work in pairs. Choose two correct answers:

Chemical element oxygen:

1.colorless gas

2.has serial number 8 (+)

3.Is part of the air

4.included in water (+)

5.Slightly heavier than air.

4. Simple substance oxygen:

1.has an atomic mass of 16

2.included in water

3.supports breathing and combustion (+)

4. formed during the decomposition of hydrogen peroxide (+).

5. Fill in the table:

General characteristics of oxygen
Being in nature
Receiving a) in the laboratory b) in industry
Physical properties

Calculate mass fraction the chemical element oxygen in sulfur oxide (VI). SO3

W = (nхAr): Mr х 100%

W (O) = (3x16): 80x100% = 60%

How to recognize which flask contains carbon dioxide and oxygen? (with the help of a smoldering splinter: in oxygen it flashes brightly, in carbon dioxide- goes out).