What is nitrogen? The mass of nitrogen. Nitrogen molecule

The nonmetallic element of the 15th group [Va] of the periodic table is nitrogen, 2 atoms of which, when combined, form a molecule, a colorless, odorless and tasteless gas that makes up most of the Earth's atmosphere and is an integral part of all living things.

History of detection

The nitrogen gas is about 4/5 of the earth's atmosphere. It was isolated during the early air research. In 1772 the Swedish chemist Karl-Wilhelm Scheele first demonstrated what nitrogen is. In his opinion, the air is a mixture of two gases, one of which he called "fiery air", since he maintained burning, and the other "unclean air", because he remained after the first was spent. It was oxygen and nitrogen. Around the same time, nitrogen was isolated by the Scottish botanist Daniel Rutherford, who first published his findings, as well as the British chemist Henry Cavendish and the British clergyman and scientist Joseph Priestley, who shared with Sheele the primacy of the discovery of oxygen. Further research has shown that the new gas is part of nitrate or potassium nitrate (KNO ₃ ) and, accordingly, it was called the nitrogene ("nitrate") by the French chemist Shaptal in 1790. Nitrogen was first attributed to the chemical elements of Lavoisier, Whose explanation of the role of oxygen in combustion denied the theory of phlogiston - popular in the XVIII century. Erroneous idea of burning. The inability of this chemical element to sustain life (in Greek ζωή) caused Lavoisier to call the gas nitrogen.

Occurrence and distribution

What is nitrogen? By the prevalence of chemical elements, it occupies the sixth place. The Earth's atmosphere is 75.51% by weight and 78.09% by volume consists of this element and is its main source for industry. The atmosphere also contains a small amount of ammonia and ammonium salts, as well as nitrogen oxides and nitric acid produced during thunderstorms, as well as in internal combustion engines. Free nitrogen is found in many meteorites, volcanic and mine gases and some mineral springs, in the sun, in stars and nebulae.

Nitrogen is also found in mineral deposits of potassium nitrate and sodium, but it is not enough to meet human needs. Another material rich in this element is the guano, which can be found in caves where there are many bats, or in dry places frequented by birds. Also nitrogen is contained in rain and soil in the form of ammonia and ammonium salts, and in sea water in the form of ammonium ions (NH ₄ ⁺ ), nitrites (NO ₂ ^- ) and nitrates (NO ₃ ^- ). On average, it is about 16% of complex organic compounds, such as proteins, present in all living organisms. Its natural content in the earth's crust is 0.3 parts per 1000. The prevalence in space is 3 to 7 atoms per silicon atom.

The largest countries producing nitrogen (in the form of ammonia) at the beginning of the XXI century were India, Russia, the United States, Trinidad and Tobago, Ukraine.

Commercial production and use

The industrial production of nitrogen is based on fractional distillation of liquefied air. The boiling point is -195.8 ° C, which is 13 ° C lower than that of oxygen, which is thus separated. Nitrogen can also be produced on a large scale by burning carbon or hydrocarbons in air and separating the resulting carbon dioxide and water from residual nitrogen. On a small scale, pure nitrogen is produced by heating the barium azide Ba (N ₃ ) ₂ . Laboratory reactions include heating a solution of ammonium nitrite (NH ₄ NO ₂ ), oxidizing ammonia with an aqueous solution of bromine or heated copper oxide :

• NH ₄ ⁺ + NO ₂ ^- → N ₂ + 2H ₂ O.
• 8NH ₃ + 3Br ₂ → N ₂ + 6NH ₄ ⁺ + 6Br ^- .
• 2NH3 + 3CuO → N2 + 3H2O + 3Cu.

Elementary nitrogen can be used as an inert atmosphere for reactions requiring the exclusion of oxygen and moisture. Liquid nitrogen is also used. Hydrogen, methane, carbon monoxide, fluorine and oxygen are the only substances that do not convert to a solid crystalline state at the boiling point of nitrogen.

In the chemical industry, this chemical element is used to prevent oxidation or other deterioration of the product, like an inert diluent of a reactive gas, to remove heat or chemicals, and also as a fire or explosion inhibitor. In the food industry, nitrogen gas is used to prevent spoilage of products, and liquid - for freeze drying and cooling systems. In the electrical industry, gas prevents oxidation and other chemical reactions, creates pressure in the cable sheath and protects the electric motors. In metallurgy, nitrogen is used in welding and soldering, preventing oxidation, carburization and decarburization. As an inactive gas it is used in the production of porous rubber, plastic and elastomers, it serves as a propellant in aerosol cans, and also creates pressure of liquid fuel in jet aircraft. In medicine, rapid freezing with liquid nitrogen is used to preserve blood, bone marrow, tissues, bacteria and sperm. He found application in cryogenic research.

Connections

Most of the nitrogen is used in the production of chemical compounds. The triple bond between the atoms of the element is so strong (226 kcal per mole, twice that of molecular hydrogen) that the nitrogen molecule hardly enters other compounds.

The main industrial method for fixing the element is the Haber-Bosch process for ammonia synthesis, developed during the First World War, in order to reduce Germany's dependence on Chilean nitrate. It includes direct synthesis of NH ₃ - a colorless gas with a sharp, irritating odor - directly from its elements.

Most of the ammonia is converted to nitric acid (HNO ₃ ) and nitrates - salts and esters of nitric acid, calcined soda (Na ₂ CO ₃ ), hydrazine (N ₂ H ₄ ) - a colorless liquid used as a propellant and in many industrial Processes.

Nitric acid is another major commercial compound of this chemical element. Colorless, highly corrosive liquid is used in the production of fertilizers, dyes, medicines and explosives. Ammonium nitrate (NH ₄ NO ₃ ) - a salt of ammonia and nitric acid - is the most common component of nitrogen fertilizers.

Nitrogen + oxygen

With oxygen, nitrogen forms a series of oxides, including nitrous oxide (N ₂ O), in which its valence is +1, oxide (NO) (+2) and dioxide (NO ₂ ) (+4). Many nitrogen oxides are extremely volatile; They are the main sources of pollution in the atmosphere. Nitrous oxide, also known as gassing gas, is sometimes used as an anesthetic. When inhaled, it causes mild hysteria. Nitrogen oxide reacts rapidly with oxygen to form a brown dioxide, an intermediate in the production of nitric acid and a powerful oxidant in chemical processes and rocket fuel.

Some nitrides formed by the combination of metals with nitrogen at elevated temperatures are also used. Nitrides of boron, titanium, zirconium and tantalum have special applications. One crystalline form of boron nitride (BN), for example, is not inferior to diamond in hardness and is poorly oxidized, therefore it is used as a high-temperature abrasive.

Inorganic cyanides contain the group CN ^- . Hydrogen cyanide, or hydrocyanic acid HCN, is an extremely unstable and extremely toxic gas that is used for fumigation, ore concentration, in other industrial processes. Dicyan (CN) _{2 is} used as an intermediate chemical and for fumigation.

Azides are compounds that contain a group of three nitrogen atoms -N ₃ . Most of them are unstable and very sensitive to shocks. Some of them, such as lead azide Pb (N ₃ ) ₂ , are used in detonators and capsules. Azides, like halogens, readily interact with other substances and form a variety of compounds.

Nitrogen is part of several thousand organic compounds. Most of them are derived from ammonia, hydrogen cyanide, cyanogen, nitrous oxide or nitric acid. Amines, amino acids, amides, for example, are derived from or closely related to ammonia. Nitroglycerin and nitrocellulose are nitric acid esters. Nitrites are prepared from nitrous acid (HNO ₂ ). Purines and alkaloids are heterocyclic compounds in which nitrogen replaces one or more carbon atoms.

Properties and reactions

What is nitrogen? This is a colorless odorless gas that condenses at -195.8 ° C into a colorless, low-viscosity liquid. The element exists as N ₂ molecules, represented as: N ::: N: for which the binding energy, equal to 226 kcal per mole, is second only to carbon monoxide (256 kcal per mole). For this reason, the activation energy of molecular nitrogen is very high, so under normal conditions the element is relatively inert. In addition, a highly stable nitrogen molecule contributes significantly to the thermodynamic instability of many nitrogen-containing compounds in which bonds, although strong enough, are inferior to molecular nitrogen bonds.

Relatively recently and unexpectedly, the ability of nitrogen molecules to serve as ligands in complex compounds was discovered. Observing that certain solutions of ruthenium complexes can absorb atmospheric nitrogen has led to the fact that a simpler and better way of fixing this element can soon be found.

Active nitrogen can be obtained by passing a low-pressure gas through a high-voltage electric discharge. The product glows yellow and is much more willing to react than the molecular one, with atomic hydrogen, sulfur, phosphorus and various metals, and is also capable of decomposing NO to N ₂ and O ₂ .

A clearer idea of what nitrogen is, can be obtained from its electronic structure, which has the form 1s ² 2s ² 2p ³ . The five electrons of the outer shells weakly shield the charge, as a result of which the effective nuclear charge is felt at a distance of the covalent radius. Nitrogen atoms are relatively small and have a high electronegativity, located between carbon and oxygen. The electronic configuration includes three half-filled external orbitals, which make it possible to form three covalent bonds. Therefore, the nitrogen atom must have an extremely high reactivity, forming stable binary compounds with most other elements, especially when the other element significantly differs in electronegativity, which gives a significant polarity to the bonds. When the electronegativity of the other element is lower, the polarity gives the nitrogen atom a partial negative charge, which frees its undivided electrons to participate in coordination bonds. When another element is more electronegative, a partially positive charge of nitrogen substantially limits the donor properties of the molecule. At a low polarity of the bond, due to the equal electronegativity of the other element, multiple connections prevail over single bonds. If the mismatch of atomic dimensions prevents the formation of multiple bonds, then the formed simple bond is likely to be relatively weak, and the connection will be unstable.

Analytical chemistry

Often the percentage of nitrogen in a gas mixture can be determined by measuring its volume after absorption of other components by chemical reagents. The decomposition of nitrates with sulfuric acid in the presence of mercury releases nitric oxide, which can be measured as a gas. Nitrogen is released from organic compounds when they burn over copper oxide, and free nitrogen can be measured as a gas after absorption of other combustion products. Kjeldahl's well-known method for determining the content of the substance we are considering in organic compounds consists in decomposing the compound with concentrated sulfuric acid (if necessary containing mercury or its oxide, as well as various salts). Thus, the nitrogen is converted to ammonium sulfate. Addition of sodium hydroxide releases ammonia, which is collected by conventional acid; The residual amount of unreacted acid is then determined by titration.

Biological and physiological significance

The role of nitrogen in living matter confirms the physiological activity of its organic compounds. Most living organisms can not use this chemical element directly and must have access to its compounds. Therefore, the fixation of nitrogen is of great importance. In nature, this is the result of two main processes. One of them is the effect of electrical energy on the atmosphere, due to which the nitrogen and oxygen molecule dissociate, which allows free atoms to form NO and NO ₂ . The dioxide then reacts with water: 3NO ₂ + H ₂ O → 2HNO ₃ + NO.

HNO ₃ dissolves and comes to Earth with rain in the form of a weak solution. Over time, the acid becomes part of the combined soil nitrogen, where it is neutralized, forming nitrites and nitrates. The N content in cultivated soils, as a rule, is restored due to the introduction of fertilizers containing nitrates and ammonium salts. Isolation of animals and plants and their decomposition returns nitrogen compounds to soil and air.

Another major process of natural fixation is the life activity of legumes. Thanks to symbiosis with bacteria, these cultures are able to convert atmospheric nitrogen directly into its compounds. Some microorganisms, such as Azotobacter Chroococcum and Clostridium pasteurianum, are able to fix N independently.

The gas itself, being inert, is harmless, except when breathing under pressure, and it dissolves in blood and other body fluids at higher concentrations. This causes a narcotic effect, and if the pressure decreases too quickly, excess nitrogen is released in the form of gas bubbles in various parts of the body. This can cause pain in the muscles and joints, fainting, partial paralysis and even death. These symptoms are called decompression sickness. Therefore, those who are forced to breathe air under these conditions should very slowly reduce the pressure to normal so that excess nitrogen exits through the lungs without the formation of bubbles. The best alternative is to use a mixture of oxygen and helium for breathing. Helium is much less soluble in body fluids, and the danger decreases.

Isotopes

Nitrogen exists in the form of two stable isotopes: ¹⁴ N (99.63%) and ¹⁵ N (0.37%). They can be separated by chemical exchange or by thermal diffusion. The mass of nitrogen in the form of artificial radioactive isotopes is in the range of 10-13 and 16-24. The most stable half-life is 10 minutes. The first artificially induced nuclear transmutation was made in 1919 by the British physicist Ernest Rutherford, who, bombarding nitrogen-14 with alpha particles, obtained the oxygen-17 nuclei and protons.

Properties

Finally, we list the main properties of nitrogen:

• Atomic number: 7.
• Atomic weight of nitrogen: 14,0067.
• Melting point: -209.86 ° C.
• Boiling point: -195.8 ° C.
• Density (1 atm, 0 ° C): 1.2506 g of nitrogen per liter.
• The usual oxidation states are -3, +3, +5.
• Electron configuration: 1s ² 2s ² 2p ³ .