Nitrogen compounds. Properties of nitrogen

Generating nitrate - so is translated from the Latin language word Nitrogenium. This is the name of nitrogen - a chemical element with atomic number 7, heading the 15th group in a long version of the periodic table. In the form of a simple substance is distributed in the composition of the air envelope of the Earth - the atmosphere. Various nitrogen compounds are found in the earth's crust and living organisms, are widely used in industries, military affairs, agriculture and medicine.

Why nitrogen was called "suffocating" and "lifeless"

As historians of chemistry suggest, the first to receive this simple substance was Henry Cavendish (1777). The scientist let the air over the hot coals, and used alkali to absorb the reaction products. As a result of the experiment, the researcher discovered a colorless, odorless gas that did not react with coal. Cavendish called it "suffocating air" for the inability to maintain breathing, as well as burning.

A modern chemist would explain that oxygen reacted with coal, carbon dioxide was formed. The remaining "suffocating" part of the air consisted mostly of N ₂ molecules. Cavendish and other scientists at that time did not yet know about this substance, although the compounds of nitrogen and saltpeter were then widely used in the economy. The scientist reported an unusual gas to his colleague, who conducted similar experiments - Joseph Priestley.

At the same time Karl Scheele drew attention to an unknown component of the air, but failed to correctly explain its origin. Only Daniel Rutherford in 1772 realized that the "suffocating" "spoiled" gas - nitrogen - present in the experiments. What a scientist consider him a pioneer - historians of science are still arguing about this.

Fifteen years after the experiments of Rutherford, the famous chemist Antoine Lavoisier proposed to replace the term "spoiled" air, referred to nitrogen, on the other - Nitrogenium. By that time it was proved that this substance does not burn, does not support breathing. Then came the Russian name "nitrogen", which is interpreted in different ways. Most often they say that the term means "lifeless". Subsequent works have refuted the widespread opinion about the properties of matter. Nitrogen compounds - proteins - the most important macromolecules in the composition of living organisms. For their construction, plants absorb from the soil the necessary elements of mineral nutrition - NO ₃ ^2- and NH ⁴⁺ ions.

Nitrogen is a chemical element

To understand the structure of the atom and properties, the periodic system (PS) helps. The chemical element in the periodic table can be used to determine the charge of the nucleus, the number of protons and neutrons (mass number). It is necessary to pay attention to the value of the atomic mass - this is one of the main characteristics of the element. The period number corresponds to the number of energy levels. In a short version of the periodic table, the group number corresponds to the number of electrons at the external energy level. Let us summarize all the data in the general characteristic of nitrogen by its position in the periodic table:

• This is a non-metallic element, located in the upper right corner of the PS.
• Chemical symbol: N.
• Sequence number: 7.
• Relative atomic mass: 14,0067.
• The formula for the volatile hydrogen compound is NH ₃ (ammonia).
• Forms a higher oxide N ₂ O ₅ , in which the valence of nitrogen is equal to V.

The structure of the nitrogen atom:

• Charge the kernel: +7.
• Number of protons: 7; Number of neutrons: 7.
• Number of energy levels: 2.
• Total number of electrons: 7; Electronic formula: 1s ² 2s ² 2p ³ .

Stable isotopes of element No. 7 and their mass numbers 14 and 15 are studied in detail. The content of atoms of the lighter one is 99.64%. In the nuclei of short-lived radioactive isotopes there are also 7 protons, and the number of neutrons varies greatly: 4, 5, 6, 9, 10.

Nitrogen in nature

In the air envelope of the Earth there are molecules of a simple substance, the formula of which is N ₂ . The content of gaseous nitrogen in the atmosphere is approximately 78.1% by volume. Inorganic compounds of this chemical element in the earth's crust are various ammonium salts and nitrates (saltpeter). Formula compounds and names of some of the most important substances:

• NH _3, ammonia.
• NO _2, nitrogen dioxide.
• NaNO _3, sodium nitrate.
• (NH ₄ ) ₂ SO _4, ammonium sulfate.

Valence of nitrogen in the last two compounds - IV. Coal, soil, living organisms also contain N atoms in a bound form. Nitrogen is an integral part of amino acid macromolecules, nucleotides of DNA and RNA, hormones and hemoglobin. The total content of a chemical element in the human body is 2.5%.

Simple substance

Nitrogen in the form of diatomic molecules is the largest by volume and mass of air in the atmosphere. The substance, the formula of which is N ₂ , does not have a smell, color and taste. This gas is more than 2/3 of the Earth's air envelope. In liquid form, nitrogen is a colorless substance that resembles water. It boils at a temperature of -195.8 ° C. M (N ₂ ) = 28 g / mol. A simple substance, nitrogen is slightly lighter than oxygen, its density through the air is close to 1.

Atoms in the molecule firmly bind 3 common electron pairs. The compound exhibits high chemical stability, which distinguishes it from oxygen and a number of other gaseous substances. In order for the nitrogen molecule to decay into its constituent atoms, it is necessary to expend energy 942.9 kJ / mol. The bond of three pairs of electrons is very strong, begins to break down when heated above 2000 ° C.

Under normal conditions, dissociation of molecules into atoms practically does not occur. The chemical inertness of nitrogen is also due to the complete absence of polarity in its molecules. They interact very weakly with one another, which is responsible for the gaseous state of the substance at normal pressure and at a temperature close to room temperature. The low chemical activity of molecular nitrogen finds application in different processes and devices where it is necessary to create an inert medium.

The dissociation of N ₂ molecules can occur under the influence of solar radiation in the upper layers of the atmosphere. An atomic nitrogen is formed, which under normal conditions reacts with certain metals and nonmetals (phosphorus, sulfur, arsenic). As a result, there is a synthesis of substances that are obtained indirectly by terrestrial conditions.

Valence of nitrogen

The outer electron layer of the atom forms 2 s and 3 p electrons. These negative particles can be given off by nitrogen when interacting with other elements, which corresponds to its reducing properties. Adding missing electrons to an octet of 3, the atom exhibits oxidative abilities. The electronegativity of nitrogen is lower, its nonmetallic properties are less pronounced than in fluorine, oxygen and chlorine. When interacting with these chemical elements, nitrogen releases electrons (oxidizes). Reaction to negative ions is accompanied by reactions with other non-metals and metals.

The typical valence of nitrogen is III. In this case, chemical bonds are formed due to attraction of external p-electrons and creation of common (binding) pairs. Nitrogen is capable of forming a donor-acceptor bond due to its unshared pair of electrons, as occurs in the NH ⁴⁺ ammonium ion.

Obtaining in the laboratory and industry

One of the laboratory methods is based on the oxidizing properties of copper oxide. The connection of nitrogen with hydrogen is used - ammonia NH ₃ . This unpleasantly smelling gas interacts with powdered copper oxide of black color. As a result of the reaction, nitrogen is released and metallic copper appears (red powder). Drops of water settle on the walls of the tube - another reaction product.

Another laboratory method in which a compound of nitrogen with metals is used is an azide, for example NaN ₃ . It turns out a gas that does not need to be cleaned of impurities.

In the laboratory, decomposition of ammonium nitrite into nitrogen and water is carried out. In order for the reaction to start, heating is required, then the process proceeds with the release of heat (exothermic). Nitrogen is contaminated with impurities, so it is purified and drained.

Nitrogen production in industry:

• Fractional distillation of liquid air - a method in which the physical properties of nitrogen and oxygen (different boiling points) are used;
• Chemical reaction of air with hot coal;
• Adsorption gas separation.

Interaction with metals and hydrogen - oxidizing properties

The inertness of strong molecules does not allow obtaining some nitrogen compounds by direct synthesis. To activate the atoms, strong heating or irradiation of the substance is necessary. Nitrogen can react with lithium at room temperature, with magnesium, calcium and sodium, the reaction only occurs when heated. Nitrides of the corresponding metals are formed.

The interaction of nitrogen with hydrogen occurs at high temperatures and pressures. A catalyst is also needed for this process. It turns out ammonia - one of the most important products of chemical synthesis. Nitrogen, as an oxidizer, exhibits in its compounds three negative oxidation states:

• -3 (ammonia and other hydrogen compounds of nitrogen - nitrides);
• -2 (hydrazine N ₂ H ₄ );
• -1 (hydroxylamine NH ₂ OH).

The most important nitride - ammonia - is obtained in large quantities in industry. The chemical inertness of nitrogen remained a big problem for a long time. Its source of raw materials were nitrates, but mineral reserves began to decline rapidly with production growth.

A great achievement of chemical science and practice was the creation of an ammonia method of nitrogen binding on an industrial scale. In special columns, direct synthesis is carried out-a reversible process between nitrogen obtained from air and hydrogen. When creating optimal conditions, shifting the balance of this reaction towards the product, using the catalyst, the yield of ammonia reaches 97%.

Interaction with oxygen - reducing properties

In order for the reaction of nitrogen and oxygen to start, strong heating is necessary. The electric arc and thunderstorm discharge in the atmosphere have sufficient energy. The most important inorganic compounds, in which nitrogen is in its positive oxidation states:

• +1 (nitric oxide (I) N ₂ O);
• +2 (nitrogen monoxide NO);
• +3 (nitric oxide (III) N ₂ O ₃ , nitrous acid HNO ₂ , its salts of nitrite);
• +4 (nitrogen dioxide (IV) NO ₂ );
• +5 (nitrogen pentoxide (V) N ₂ O ₅ , nitric acid HNO ₃ , nitrates).

Importance in nature

Plants absorb ammonium ions and nitrate anions from the soil, use for chemical reactions the synthesis of organic molecules, constantly going in cells. Atmospheric nitrogen can be assimilated by nodule bacteria - microscopic creatures that form growths on the roots of legumes. As a result, this group of plants receives the necessary element of nutrition, enriches the soil.

During tropical showers, oxidation reactions of atmospheric nitrogen occur. Oxides dissolve with the formation of acids, these nitrogen compounds in water enter the soil. Due to the cycle of the element in nature, its reserves in the earth's crust and air are constantly replenished. Complex organic molecules containing nitrogen in their composition are decomposed by bacteria into inorganic constituents.

Practical use

The most important nitrogen compounds for agriculture are readily soluble salts. Assimilated plants urea, nitrate (sodium, potassium, calcium), ammonium compounds (aqueous solution of ammonia, chloride, sulfate, ammonium nitrate).
The inert properties of nitrogen, the inability of plants to assimilate it from the air, lead to the need to annually make large doses of nitrates. Parts of the plant organism are able to store the macronutrient of food "for future use", which worsens the quality of the produce. Excess nitrates in vegetables and fruits can cause people to have poisoning, the growth of malignant tumors. In addition to agriculture, nitrogen compounds are used in other industries:

• For obtaining medicines;
• For the chemical synthesis of high-molecular compounds;
• In the production of explosives from trinitrotoluene (TNT);
• For the production of dyes.

NO oxide is used in surgery, the substance has an analgesic effect. The loss of sensations during the inhalation of this gas was noticed by the first researchers of the chemical properties of nitrogen. This is how the trivial name "amusing gas" appeared.

The problem of nitrates in agricultural products

In the salts of nitric acid - nitrates - contains the singly charged NO ^3- anion. Until now, the old name of this group of substances - saltpeter is used. Nitrates are used for fertilizing fields, in greenhouses, orchards. They bring them in the early spring before sowing, in the summer - in the form of liquid fertilizing. The substances themselves do not pose a great danger to people, but in the body they turn into nitrites, then into nitrosamines. Nitrite ions NO ^2- are toxic particles, they cause oxidation of ferrous iron in molecules of hemoglobin to trivalent ions. In such a state, the main substance of human and animal blood is not capable of transferring oxygen and removing carbon dioxide from tissues.

What is dangerous nitrate contamination of food for human health:

• Malignant tumors arising from the conversion of nitrates to nitrosamines (carcinogens);
• Development of ulcerative colitis,
• Hypotension or hypertension;
• Heart failure;
• A bleeding disorder
• Lesions of the liver, pancreas, development of diabetes;
• Development of renal failure;
• Anemia, impaired memory, attention, intelligence.

Simultaneous use of different products with high doses of nitrates leads to acute poisoning. Sources can be plants, drinking water, ready-made meat dishes. Soaking in pure water and cooking can reduce the content of nitrates in food. The researchers found that higher doses of hazardous compounds are noted in immature and greenhouse plant products.

Phosphorus is an element of the subgroup of nitrogen

Atoms of chemical elements that are in the same vertical column of the periodic system exhibit common properties. Phosphorus is located in the third period, it belongs to group 15, like nitrogen. The structure of the atoms of the elements is similar, but there are differences in properties. Nitrogen and phosphorus exhibit a negative degree of oxidation and valence III in their compounds with metals and hydrogen.

Many phosphorus reactions occur at ordinary temperatures, this is a chemically active element. Interacts with oxygen to form higher oxide P ₂ O ₅ . An aqueous solution of this substance has the properties of an acid (metaphosphoric acid). When it is heated, orthophosphoric acid is obtained. It forms several types of salts, many of which serve as mineral fertilizers, for example superphosphates. The compounds of nitrogen and phosphorus form an important part of the cycle of substances and energy on our planet, they are used in industrial, agricultural and other fields of activity.