The oxygen formula. Periodic table of Mendeleev - oxygen

The chemical element oxygen is in the second period of the VI-th main group of the obsolete short version of the periodic table. According to the new numbering standards, this is the 16th group. The corresponding decision was made by IUPAC in 1988. The formula for oxygen as a simple substance is O ₂ . Let's consider its basic properties, its role in nature and economy. Let us begin with the characteristics of the entire group of the periodic system, which is headed by oxygen. The element differs from its related chalcogenes, and water differs from hydrogen compounds of sulfur, selenium and tellurium. Explanation of all the distinctive features can be found only after learning about the structure and properties of the atom.

Chalcogenes are related elements of oxygen

Similar atoms on the properties form one group in the periodic system. Oxygen leads the family of chalcogenes, but differs from them in a number of properties.

The atomic mass of oxygen - the founder of the group - is 16 a. The chalcogenes in the formation of compounds with hydrogen and metals exhibit their usual oxidation state: -2. For example, in the water (H ₂ O), the oxidation number of oxygen is -2.

The composition of typical hydrogen compounds of chalcogenes corresponds to the general formula: H ₂ R. When these substances are dissolved, acids are formed. Only the hydrogen compound of oxygen-water-has special properties. According to the scientists, this unusual substance is a very weak acid, and a very weak base.

Sulfur, selenium and tellurium have typical positive oxidation states (+4, +6) in compounds with oxygen and other nonmetals having high electronegativity (EO). The composition of chalcogen oxides reflects the general formulas: RO ₂ , RO ₃ . The corresponding acids have the composition: H ₂ RO ₃ , H ₂ RO ₄ .

Elements correspond to simple substances: oxygen, sulfur, selenium, tellurium and polonium. The first three representatives show non-metallic properties. The oxygen formula is O ₂ . Allotropic modification of the same element is ozone (O ₃₎ . Both modifications are gases. Sulfur and selenium are solid non-metals. Tellurium is a metalloid substance, conductor of an electric current, polonium is a metal.

Oxygen is the most common element

The total content of elemental atoms in the earth's crust is approximately 47% (by weight). Oxygen is found both in a free form, and in the composition of numerous compounds. A simple substance, the formula of which is O ₂ , is contained in the atmosphere, amounting to 21% of air (by volume). Molecular oxygen is dissolved in water, located between soil particles.

We already know that there is another kind of existence of the same chemical element in the form of a simple substance. This ozone is a gas forming at a height of about 30 km from the surface of the earth a layer, often called the ozone screen. Bound oxygen enters the water molecules, into many rocks and minerals, organic compounds.

The structure of the oxygen atom

The Periodic Table of Mendeleev contains complete information about oxygen:

1. The serial number of the element is 8.
2. The core charge is +8.
3. The total number of electrons is 8.
4. The electronic oxygen formula is 1s ² 2s ² 2p ⁴ .

In nature, there are three stable isotopes that have the same ordinal number in the periodic table, the same composition of protons and electrons, but different numbers of neutrons. The isotopes are denoted by the same symbol, O. For comparison, let us give a diagram reflecting the composition of the three isotopes of oxygen:

Properties of oxygen - chemical element

At the 2p-sublevel of the atom, there are two unpaired electrons, which explains the appearance of oxidation states -2 and +2. Two paired electrons can not be disconnected, so that the degree of oxidation increases to +4, as in sulfur and other chalcogenes. The reason is the absence of a free sublevel. Therefore, in compounds, the chemical element oxygen does not exhibit a valence and oxidation degree equal to the group number in the short version of the periodic system (6). The usual oxidative number is -2.

Only in compounds with fluorine, oxygen exhibits a non-characteristic positive oxidation state of +2. The EO value of two strong non-metals is different: EO (O) = 3.5; EO (F) = 4. As a more electronegative chemical element, fluorine retains its electrons more and attracts valence particles at the external energy level of the oxygen atom. Therefore, in the reaction with fluorine, oxygen is a reducing agent, it gives off electrons.

Oxygen is a simple substance

The English explorer D. Priestley in 1774, during the experiments, isolated gas in the decomposition of mercury oxide. Two years earlier, the same substance was obtained in pure form by K. Scheele. Only a few years later the French chemist A. Lavoisier established that he is a part of the air for gas, he studied properties. The chemical formula of oxygen is O ₂ . We reflect in the record of the composition of matter the electrons participating in the formation of a nonpolar covalent bond - O :: O. We replace each binding electron pair with one line: 0 = 0. This oxygen formula clearly shows that the atoms in the molecule are connected between two common pairs of electrons.

We perform simple calculations and determine what is the relative molecular mass of oxygen: Mr (O2) = Ar (O) x2 = 16x2 = 32. For comparison: Mr (air) = 29. The chemical formula for oxygen differs from the ozone formula Per one oxygen atom. Hence, Mr (O ₃ ) = Ar (O) x 3 = 48. Ozone is 1.5 times heavier than oxygen.

Physical properties

Oxygen is a gas without color, taste and smell (at ordinary temperature and atmospheric pressure). The substance is slightly heavier than air; Dissolves in water, but in small amounts. The melting point of oxygen is negative and is -218.3 ° C. The point at which liquid oxygen again turns into gaseous is its boiling point. For molecules of O _{2, the} value of this physical quantity reaches -182.96 ° C. In liquid and solid state, oxygen acquires a light blue color.

Obtaining oxygen in the laboratory

When the oxygen-containing substances, such as potassium permanganate are heated, a colorless gas is released, which can be collected in a flask or a test tube. If you bring into the pure oxygen a lit beam, then it burns more brightly than in the air. Two other laboratory methods for obtaining oxygen - the decomposition of hydrogen peroxide and potassium chlorate (berthollet salt). Let's consider the scheme of the device, which is used for thermal decomposition.

In a test tube or a round-bottomed flask, it is necessary to pour a little bit of bertholet salt, to close it with a stopper with a gas outlet tube. Its opposite end should be directed (under water) into the upside down flask. The neck should be lowered into a wide glass or crystallizer filled with water. When the test tube with the Bertolet salt is heated, oxygen is released. On the gas pipe he enters the flask, displacing water from it. When the flask is filled with gas, it is closed with a stopper under the water and turned over. The oxygen obtained in this laboratory experiment can be used to study the chemical properties of a simple substance.

Combustion

If the laboratory burns substances in oxygen, then you need to know and comply with fire regulations. Hydrogen instantly burns in the air, and mixed with oxygen in a ratio of 2: 1, it is explosive. Combustion of substances in pure oxygen occurs much more intensively than in air. This phenomenon is explained by the composition of the air. Oxygen in the atmosphere is slightly more than 1/5 of the fraction (21%). Combustion is the reaction of substances with oxygen, as a result of which different products are formed, mainly oxides of metals and nonmetals. Fire mixtures O ₂ with combustible substances, in addition, the resulting compounds can be toxic.

Combustion of a conventional candle (or match) is accompanied by the formation of carbon dioxide. The following experience can be conducted at home. If you burn a substance under a glass jar or a large glass, the burning will stop as soon as all the oxygen is consumed. Nitrogen does not support breathing and burning. Carbon dioxide, an oxidation product, no longer reacts with oxygen. Transparent calcareous water can detect the presence of carbon dioxide after the burning of the candle. If you pass the combustion products through calcium hydroxide, the solution becomes cloudy. There is a chemical reaction between the calcareous water and carbon dioxide, resulting in insoluble calcium carbonate.

Production of oxygen on an industrial scale

The cheapest process, as a result of which air-free O ₂ molecules are obtained, is not connected with chemical reactions. In industry, say, at metallurgical plants, air at low temperature and high pressure is liquefied. Such important components of the atmosphere, as nitrogen and oxygen, boil at different temperatures. Separate the air mixture with gradual heating to normal temperature. First, nitrogen molecules are separated, then oxygen. The separation method is based on different physical properties of simple substances. The formula for the simple matter of oxygen is the same as before the cooling and liquefaction of air, O ₂ .

As a result of some electrolysis reactions, oxygen is also released, it is collected above the corresponding electrode. Gas is needed by industrial, construction companies in large quantities. The need for oxygen is constantly growing, especially the chemical industry needs it. The obtained gas is stored for industrial and medical purposes in steel cylinders equipped with marking. Capacities with oxygen are painted blue or blue to distinguish them from other liquefied gases - nitrogen, methane, ammonia.

Chemical calculations by formula and reaction equations involving O ₂ molecules

The numerical value of the molar mass of oxygen coincides with another value - the relative molecular mass. Only in the first case there are units of measurement. Briefly, the formula for the substance of oxygen and its molar mass should be written as follows: M (O ₂ ) = 32 g / mol. Under normal conditions, I pray for any gas that corresponds to a volume of 22.4 liters. Hence, 1 mole of O ₂ is 22.4 liters of substance, 2 moles of O ₂ - 44.8 liters. By the equation of the reaction between oxygen and hydrogen, it can be seen that 2 moles of hydrogen and 1 mole of oxygen interact:

If 1 mole of hydrogen participates in the reaction, the volume of oxygen will be 0.5 mole • 22.4 l / mol = 11.2 l.

The role of O ₂ molecules in nature and human life

Oxygen is consumed by living organisms on Earth and participates in the circulation of substances over 3 billion years. This is the main substance for respiration and metabolism, it helps decompose the molecules of nutrients, synthesizes the energy necessary for organisms. Oxygen is constantly consumed on Earth, but its stocks are replenished thanks to photosynthesis. Russian scientist K. Timiryazev believed that thanks to this very process there is still life on our planet.

The role of oxygen in nature and economy is great:

• Absorbed in the process of breathing by living organisms;
• Participates in the reactions of photosynthesis in plants;
• Is part of organic molecules;
• Processes of decay, fermentation, rusting occur with the participation of oxygen, which acts as an oxidizer;
• It is used for obtaining valuable products of organic synthesis.

Liquefied oxygen in cylinders is used for cutting and welding metals at high temperatures. These processes are carried out at machine-building plants, transport and construction enterprises. To carry out work under water, underground, at high altitude in an airless space, people also need O ₂ molecules. Oxygen cushions are used in medicine to enrich the air composition inhaled by sick people. The gas for medical purposes differs from the technical practically in the absence of foreign impurities, odor.

Oxygen is an ideal oxidizer

Oxygen compounds with all the chemical elements of the periodic table are known, except for the first representatives of the family of noble gases. Many substances directly react with O atoms, excluding halogens, gold and platinum. Of great importance are phenomena involving oxygen, which are accompanied by the release of light and heat. Such processes are widely used in everyday life, industry. In metallurgy, the interaction of ores with oxygen is called roasting. Pre-crushed ore is mixed with air enriched with oxygen. At high temperatures, metals are reduced from sulphides to simple substances. So get iron and some non-ferrous metals. The presence of pure oxygen increases the speed of technological processes in different branches of chemistry, engineering and metallurgy.

The appearance of a cheap method of obtaining oxygen from air by the method of separation into components at low temperature stimulated the development of many directions of industrial production. Chemists consider O ₂ molecules and O atoms as ideal oxidizing agents. These are natural materials, they are constantly renewed in nature, do not pollute the environment. In addition, chemical reactions involving oxygen most often result in the synthesis of another natural and safe product - water. The role of O ₂ in the neutralization of toxic industrial wastes, the purification of water from pollution is great. In addition to oxygen, its allotropic modification - ozone - is used for disinfection. This simple substance has a high oxidative activity. When ozonizing water, pollutants decompose. Ozone also has a harmful effect on the pathogenic microflora.