Oxygen found in nature. Oxygen - a characteristic of the element, prevalence in nature, physical and chemical properties, obtaining

Chemistry lesson Grade 8

Subject: Oxygen, its general characteristics. Finding in nature. Obtaining oxygen and its physical properties.

The purpose of the lesson: continue the formation of the concepts of "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 the element according to the table 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" using oxygen as an example. Be able to characterize the physical properties and methods of collecting oxygen.

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

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

The main activities of students. Describe the 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. Obtaining oxygen from hydrogen peroxide.

During the classes

Learning new material.

1. Frontal conversation:

What gas supports respiration 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 of the chemical element oxygen:

Chemical sign (O).

Relative atomic mass (16).

Valence (II).

Chemical formula of a simple substance (O2).

Relative molecular weight of a simple substance (32).

Give a description of 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 common 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 (Mr (O2)=2x16=32, p air=29).

2. Experiments on obtaining oxygen.

Obtaining in the laboratory.

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

The scientist decided to investigate the effect of the resulting gas on the flame of a candle: under the influence of this gas, the flame of the candle became dazzlingly bright, and an iron wire burned in the stream of the resulting 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 will get this gas from hydrogen peroxide. To observe the physical properties of oxygen, we repeat the rules safety technology.

We put a little manganese (IV) oxide MnO2 into a test tube with a solution of hydrogen peroxide, a violent reaction begins with the release of oxygen. We confirm the release of oxygen with 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 itself consumed.

Definition:

Substances that speed up chemical reactions, but are not themselves consumed 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 oxygen production reaction - the decomposition reaction when heated potassium chlorate KClO3 (bertolet salt): 2KSlO3 MnO2 2KSl + 3O2

3. Work with the textbook:

Us. 75 read about the use of catalysts in industry.

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

with. 75 read the article of the textbook "obtaining in industry". On what physical property of oxygen is this method of its production based? (liquid oxygen has a higher boiling point than liquid nitrogen, so the nitrogen will evaporate and the oxygen will remain).

II.Consolidation of knowledge and skills.

What substances are called catalysts?

with. 76 test tasks.

Work in pairs. Choose two correct answers:

Chemical element oxygen:

1. colorless gas

2. has serial number 8 (+)

3. part of the air

4. is part of the water (+)

5. slightly heavier than air.

4. Simple substance oxygen:

1. has an atomic mass of 16

2. is part of the water

3. supports breathing and burning (+)

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

5. Fill in the table:

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

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

W= (nxAr): Mr x 100%

W (O) \u003d (3x16): 80x100% \u003d 60%

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

Four elements - "chalcogen" (i.e. "giving birth to copper") head the main subgroup of group VI (according to the new classification - the 16th group) of the periodic system. In addition to sulfur, tellurium and selenium, they also include oxygen. Let's take a closer look at the properties of this most common element on Earth, as well as the use and production of oxygen.

Element abundance

In a bound form, oxygen is included in the chemical composition of water - its percentage is about 89%, as well as in the composition of the cells of all living beings - plants and animals.

In the air, oxygen is in a free state in the form of O2, occupying a fifth of its composition, and in the form of ozone - O3.

Physical properties

Oxygen O2 is a colorless, tasteless and odorless gas. It is slightly soluble in water. The boiling point is 183 degrees below zero Celsius. In liquid form, oxygen has a blue color, and in solid form it forms blue crystals. The melting point of oxygen crystals is 218.7 degrees below zero Celsius.

Chemical properties

When heated, this element reacts with many simple substances, both metals and non-metals, while forming the so-called oxides - compounds of elements with oxygen. in which elements enter with oxygen is called oxidation.

For example,

4Na + O2= 2Na2O

2. Through the decomposition of hydrogen peroxide when it is heated in the presence of manganese oxide, which acts as a catalyst.

3. Through the decomposition of potassium permanganate.

The production of oxygen in industry is carried out in the following ways:

1. For technical purposes, oxygen is obtained from air, in which its usual content is about 20%, i.e. fifth part. To do this, the air is first burned, obtaining a mixture with a liquid oxygen content of about 54%, liquid nitrogen - 44% and liquid argon - 2%. These gases are then separated by a distillation process using a relatively small interval between the boiling points of liquid oxygen and liquid nitrogen - minus 183 and minus 198.5 degrees, respectively. It turns out that nitrogen evaporates before oxygen.

Modern equipment ensures the production of oxygen of any degree of purity. Nitrogen, which is obtained by separating liquid air, is used as a raw material in the synthesis of its derivatives.

2. also gives oxygen to a very pure degree. This method has become widespread in countries with rich resources and cheap electricity.

Application of oxygen

Oxygen is the most important element in the life of our entire planet. This gas, which is contained in the atmosphere, is consumed in the process by animals and humans.

Obtaining oxygen is very important for such areas of human activity as medicine, welding and cutting of metals, blasting, aviation (for breathing people and for the operation of engines), metallurgy.

In the process of human economic activity, oxygen is consumed in large quantities - for example, when burning various types of fuel: natural gas, methane, coal, wood. In all these processes, it is formed. At the same time, nature has provided for the process of natural binding of this compound through photosynthesis, which takes place in green plants under the influence of sunlight. As a result of this process, glucose is formed, which the plant then uses to build its tissues.

The content of the article

OXYGEN, O (oxygenium), a chemical element of the VIA subgroup of the Periodic Table of Elements: O, S, Se, Te, Po, is 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 of approx. 50% (wt.) and in the hydrosphere 88.8% (wt.).

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

History 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 was an element. Oxygen addition reactions are described in the scientific works of S. Gales (1731) and P. Bayen (1774). The studies of K. Scheele in 1771–1773 of the interaction of metals and phosphorus with oxygen deserve special attention. J. Priestley reported the discovery of oxygen as an element in 1774, a few months after Bayen reported 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 the 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 for the identification of certain molecules, as well as for biochemical and medical-chemical studies (a method for studying non-radioactive traces). The third non-radioactive oxygen isotope 17 8 O (0.04%) contains 9 neutrons and has a mass number of 17. After the mass of the carbon isotope 12 6 C was accepted by the International Commission as the standard atomic mass in 1961, 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, which was assumed to be 16,000 for a mixture of three natural oxygen isotopes. Physicists took the mass number of the oxygen isotope 16 8 O as a standard unit of atomic mass, therefore, according to the physical scale, the average atomic mass of oxygen was 16.0044.

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

Molecular oxygen.

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

Electronic structure.

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

Reactions.

Under appropriate conditions, molecular oxygen reacts with almost any element except the noble gases. However, under room conditions, only the most active elements react with oxygen rather quickly. It is likely that most 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 alkali (Li, Na, K) and alkaline earth (Ca, Sr, Ba) metals react with molecular oxygen to form peroxides:

Receipt and application.

Due to the presence of free oxygen in the atmosphere, the most effective method of its extraction is the liquefaction of air, from which impurities, CO 2 , dust, etc. are removed. chemical and physical methods. The cyclic process includes compression, cooling and expansion, which leads to the liquefaction of air. With a slow rise in temperature (fractional distillation), liquid air evaporates first noble gases (the most difficult to liquefy), then nitrogen, and liquid oxygen remains. As a result, liquid oxygen contains traces of noble gases and a relatively high 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 oxidizer for kerosene and other fuels in rockets and spacecraft. The steel industry uses oxygen gas to blow iron through the Bessemer process to remove C, S and P impurities quickly and efficiently. Oxygen blast produces steel faster and better than air blast. Oxygen is also used for welding and cutting metals (oxy-acetylene flame). Oxygen is also used in medicine, for example, to enrich the respiratory environment of patients with difficulty breathing. 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 obtaining oxygen is the 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 obtaining oxygen, proposed by J. Priestley, is the thermal decomposition of heavy metal oxides: 2HgO ® 2Hg + O 2 . For this, Priestley focused the sun's rays on mercury oxide powder. 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 calcination, makes it possible to maintain the required temperature and dissociation rate, and MnO 2 itself does not change during 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 in heating BaO in air until BaO 2 was formed, followed by thermal decomposition of the peroxide. The thermal decomposition method retains its importance 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, °C	–183,0
Density
solid, g / cm 3 (at t pl)	1,27
liquid g / cm 3 (at t kip)	1,14
gaseous, g / dm 3 (at 0 ° C)	1,429
relative to air	1,105
critical a, g / cm 3	0,430
Critical temperature a, °C	–118,8
Critical pressure a, atm	49,7
Solubility, cm 3 /100 ml of 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 (O 2–)	1,40
Ionization potential, V
first	13,614
second	35,146
Electronegativity (F=4)	3,5
a The temperature and pressure at which the density of a gas and a liquid is the same.

physical properties.

Oxygen under normal conditions is a colorless, odorless and tasteless gas. Liquid oxygen has a pale blue color. Solid oxygen exists in at least three crystalline modifications. Gaseous oxygen is soluble in water and probably forms unstable compounds such as O 2 H H 2 O, and possibly O 2 H 2H 2 O.

Chemical properties.

As already mentioned, the chemical activity of oxygen is determined by its ability to dissociate into O atoms, which are highly reactive. Only the most active metals and minerals react with O 2 at a high rate at low temperatures. The most active alkali (IA subgroups) and some alkaline earth (IIA subgroups) metals form peroxides such as NaO 2 and BaO 2 with O 2 . Other elements and compounds react only with the dissociation product O 2 . Under suitable conditions, all elements, except for the noble gases and the 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 accepts two electrons to the outer level to form a stable outer electron shell, forming an O 2– ion. In alkali metal oxides, predominantly ionic bonds are formed. It can be assumed that the electrons of these metals are almost entirely drawn to oxygen. In oxides of less active metals and non-metals, the transition of electrons is incomplete, and the negative charge density on oxygen is less pronounced, so the bond is less ionic or more covalent.

During the oxidation of metals with oxygen, heat is released, the magnitude of which correlates with the strength of the M–O bond. During the oxidation of some non-metals, heat is absorbed, which indicates their weaker bonds with oxygen. Such oxides are thermally unstable (or less stable than ionically bonded oxides) and are often highly reactive. The table shows for comparison the values of the enthalpies of formation 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 oxides of alkali metals decrease with an increase in the atomic radius of the metal; So, t pl (Cs 2 O) t pl (Na 2 O). Oxides dominated by ionic bonding 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 nonmetals. Heavy metal oxides in the highest oxidation state during 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 oxidizers.

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 non-metal oxides in aqueous solutions form acids containing an 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 , N V 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 are oxidized (burned) to CO 2 and H 2 O when slightly heated. 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):

(C6H10O5) n + 6n O 2 ® 6 n CO2+5 n H 2 O + thermal 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 (stone 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. To initiate a reaction, a slight activation of the reaction, such as a blow or a shake, is sufficient. In these reactions, oxides are also combustion products, but they are all gaseous and expand rapidly at a high final temperature of the process. 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 .

Oxides of metals or non-metals with lower oxidation states of an element react with oxygen to form oxides of high oxidation states 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 an 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 produce oxygen. Moisture from the exhaled air releases oxygen in the respirator, and KOH absorbs CO 2 . The production of CaO oxide and calcium hydroxide Ca(OH) 2 is a 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 life processes requires special consideration of this substance WATER, ICE AND STEAM) . As already mentioned, in the direct interaction of oxygen and hydrogen under conditions of, for example, a spark discharge, an explosion and the formation of water occur, with the release of 143 kJ/(mol H 2 O).

The water molecule has an almost tetrahedral structure, the H–O–H angle is 104° 30°. 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 having 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 addition of a particle with a positive charge. Therefore, when the active metal (or its oxide) acts 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-metal particle that has a large positive charge, resulting in a low-charged particle that is more stable, for example:

°C a dark purple solid is formed. Liquid ozone is slightly 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 an 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 a good disinfectant and is used to purify water and as a bleach, improves the condition of the atmosphere in closed systems, disinfects objects and food, accelerates the ripening of grains and fruits. In a chemical laboratory, an ozonator is often used to produce ozone, which is needed for some methods of chemical analysis and synthesis. Rubber is easily destroyed even under the influence of low concentrations of ozone. In some industrial cities, a significant concentration of ozone in the air leads to rapid deterioration of rubber products if they are not protected with antioxidants. Ozone is highly toxic. Constant inhalation of air even with very low concentrations of ozone causes headaches, nausea and other unpleasant conditions.

Oxygen is a chemical element whose properties will be discussed in the next few paragraphs. Let us turn to the Periodic System of chemical elements of D.I. Mendeleev. The element oxygen is located in period 2, group VI, the main subgroup.

It also states that the relative atomic mass of oxygen is 16.

By the serial number of oxygen in the Periodic System, one 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 waters are 89% oxygen by mass. 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°С oxygen condenses into a clear mobile liquid of a pale blue color.

If liquid oxygen is cooled even more, then at a temperature -218°С 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°С- 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. The chemical formula of ozone is 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 to disinfect 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 also be formed in the upper layers of the Earth's atmosphere: due to exposure to solar radiation, water vapor partially decomposes to form 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 amount 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

Oxygen formsperoxides with an oxidation state of −1.
- For example, peroxides are obtained by burning 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 elevated pressures and temperatures:
Na 2 O 2 + O 2 → 2NaO 2

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

And he dioxygenyl O 2 + has an oxidation state of +1/2. Get by 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 (Dioxydifluoride), O 2 F 2 , unstable, oxidation state +1. 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 its free form, the element exists in two allotropic modifications: O 2 and O 3 (ozone).

Application of oxygen

The widespread industrial use of oxygen began in the middle of the 20th century, after the invention of turboexpanders - 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 of metals

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

Rocket fuel

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

In medicine

Oxygen is used to enrich respiratory gas mixtures in case of respiratory failure, to treat asthma, in the form of oxygen cocktails, oxygen pillows, etc.

In the food industry

In the food industry, oxygen is registered as a food additive. E948, as propellant and packaging gas.

The biological role of oxygen

Living beings breathe oxygen in the air. Oxygen is widely used in medicine. In cardiovascular diseases, to improve metabolic processes, oxygen foam (“oxygen cocktail”) is introduced into the stomach. Subcutaneous oxygen administration is used for trophic ulcers, elephantiasis, gangrene and other serious diseases. Artificial enrichment with ozone is used to disinfect and deodorize the air and purify drinking water. The radioactive isotope of oxygen 15 O is used to study the rate of blood flow, pulmonary ventilation.

Toxic oxygen derivatives

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

Isotopes 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 number of 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 structure of the atomic nucleus, have a special stability.

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 (controversial half-life data from 10 minutes 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. Since ancient times, it has been known that air is needed for combustion, but for many centuries the combustion process remained incomprehensible. Only in the XVII century. Mayow and Boyle, independently of each other, expressed the idea that the air contains some substance that supports combustion, but this completely rational hypothesis was not developed at that time, since the concept of combustion as a process of connecting a burning body with a certain constituent part of the air seemed to while contradicting such an obvious act as the fact that during combustion the decomposition of a burning body into elementary components takes place. It is on this basis at the turn of the XVII century. the theory of phlogiston, created by Becher and Stahl, arose. With the advent of the chemical-analytical period in 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 field—combustion, as well as respiration, again attracted the attention of researchers. The discovery of various gases and the establishment of their important role in chemical processes was one of the main stimuli for the systematic studies of combustion processes 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 burning glass, obtained a gas in which the candle burned more brightly than in ordinary air, and the smoldering torch flashed. Priestley determined 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 other methods. Scheele called this gas fiery air (Feuerluft). Scheele was able to make a report on his discovery only in 1777.

In 1775, Lavoisier reported to the Paris Academy of Sciences that he had succeeded in obtaining "the purest part of the air that surrounds us" and described the properties of this part of the air. At first, Lavoisier called this “air” an empirical, vital (Air empireal, Air vital) base of vital air (Base de l "air vital). The almost simultaneous discovery of oxygen by several scientists in different countries caused disputes about priority. Priestley was especially persistent in recognizing himself as a discoverer "In essence, these disputes have not ended so far. A detailed study of the properties of oxygen and its role in the processes of combustion and the formation of oxides led Lavoisier to the incorrect conclusion that this gas is an acid-forming principle. In 1779, Lavoisier, in accordance with this conclusion introduced a new name for oxygen - the acid-forming principle (principe acidifiant ou principe oxygine).The word oxygine appearing in this complex name was derived by Lavoisier from Greek acid and "I produce."