Nitrogen, symbol N, chemical formula N2 is colourless, odourless, tasteless, nonmetallic gas, and essential constituent of the living matter or group-15 periodic table element in chemistry. It is the most plentiful substance (78 percent by volume and 75 percent by weight) in the earth atmosphere as dinitrogen gas (N2) but the abundance of nitrogen in rocks and soils of the earth environment is remarkably low (about 19 ppm) comparable to gallium (Ga), niobium (Nb) and lithium (Li). Only nitrogenous minerals like KNO3 (saltpeter) and NaNO3 (Chile saltpeter) are isolated via nitric acid by the action of nitrifying or fixation bacteria.
Discovery of nitrogen
Carl Wilhelm Scheele and Henry Cavendish had independently discovered and isolated nitrogen but the credit of discovery was given to Scottish physician Daniel Rutherford in 1772. Rutherford has given this credit because his work was published first in a science journal. The name nitrogen was given by French chemist Jean-Antoine-Claude Chaptal in 1790 because it was found in nitric acid and nitrate compounds. Major deposits of nitrate occur in Bolivia, Italy, Spain, Russia, and some regions of India. The major human interference occurs through artificial fixation for the manufacture of fertilizers to meet the increasing demand for food for the growing human family.
Properties of nitrogen gas
The chemistry of nitrogen (atomic number = 7) describes that the atom may gain the next noble gas electronic configuration by gaining three electrons and forming N-3 ion (oxidation number = -3). However, such electron attachment involves a high positive enthalpy change. Therefore, the formation of nitride ion (N-3) requires 2130 kJ mol-1 energy and occurs only in salt-like nitrides of the strongly electropositive metals like lithium (Li), beryllium (Be), magnesium (Mg), calcium (Ca), etc. Most of the chemical compounds formed by nitrogen are covalent compounds with the oxidation state +3 or +5 but the common oxidation number of the element covering the wide range from -3 (in NH3) to +5 (HNO3). Due to the non-availability of energetically vacant d-orbitals, it has no scope for valence expansion.
In learning chemistry, naturally occurring nitrogen exists mainly of two sable isotopes like 14N and 15N with the relative abundance 14N/15N ∼ 272:1. These radioactive isotopes may be prepared or separated by an exchange reaction or by thermal diffusion. A British physicist, Ernest Rutherford in 1919 first introduced artificial facts of radioactive nuclear reaction by the bombardment of the alpha ray with N-14 isotope to form O-17 and protons particles.
Industrially or commercially large amounts of nitrogen are obtained during the isolation of oxygen by fractional distillation of liquid air. Nitrogen molecule boils off before oxygen because its boiling point lower (N2: -195.8 °C; O2: -183.1 °C). The product usually contains a fraction of argon. Nitrogen is yield in the laboratory by heating ammonium nitrate (NH4NO2) solutions, oxidation of ammonia by bromine water or hot cupric oxide. Small scale or very pure nitrogen is obtained by heating barium azide, Ba(N3)2, or sodium azide (NaN3). It can also be produced on a large scale by burning carbon or hydrocarbon in the air, the produced carbon dioxide and water are separated from the mixture of nitrogen gas.
What is nitrogen used for?
Elemental nitrogen is largely used to provide an inert atmosphere in metallurgy and various chemical industries like the iron and steel industry for welding, soldering, and brazing, petrochemical industry (as a purge). In the liquid state, nitrogen is used in low-temperature machining, grinding of rubbers and rubber-like substances, preservation of biological specimens, and similar low-temperature applications.
In medicine, liquid nitrogen is used as a refrigerant for rapid freezing to preserve blood, bone marrow, tissue, bacteria, and semen. A large scale of nitrogen is used in the chemical industry for the manufacture of ammonia and calcium cyanamide, useful chemicals for cryogenic research, an inhibitor of fire, or explosions.
Nitrogen fixation process
It is an important type of chemical element for the growth of plant and animal life in nature and continuously interchange between the atmosphere and biosphere. About 60 percent of nitrogen input into the soil by the action of nitrifying bacteria (Rhizobium, Anabaena, Nostoc, Azotobactor, and Clostridium pastorium) which convert dinitrogen directly into nitrates or ammonium salts. Rhizobium is the most important bacteria in this category which lives symbiotically in the nodules or roots of certain plants like Leguminosae, pea, bean, etc. The nitrogen-fixing enzyme nitrogenase in nature fixed N2 into the soil is subsequently greater than the artificial fixing through the Haber process (150 million tonnes vs 120 million tonnes).
Artificial fixation is used to growing nitrogen into the soil for the production of large amounts of food for the ever-increasing population of the world. The main procedure involves the Haber process for the manufacture of ammonia which converted nitric acid and other fertilizer. Lighting in the upper atmosphere leads to the formation of NO and NO2, which is carried by nitric acid rain to the soil. To balancing the nitrogen cycle in nature, it returns to the atmosphere by the following major steps, death or decay of plants and animals, found in the combustion of wood, coal, and petroleum. The drainage of surface water carries some nitrogen gas into the sea which uses to support the common marine life.