Nitrogen (Z=7): The Abundant and Inert Element in the Atmosphere
The Essential Role of Nitrogen
Nitrogen (symbol N, atomic number 7) is a chemical element abundant in Earth's atmosphere and fundamental to life on Earth. Although it is inert in its molecular form (N₂), it is essential for many biological and industrial processes.
Contribution of Nitrogen to Vital Processes
Organisms do not consume atmospheric N₂ (an extremely stable form). Only certain nitrogen-fixing bacteria (diazotrophs) convert it into biologically usable NH₃. Consequence of a deficiency: Progressive deterioration of biological functions (deficit in proteins, DNA, etc.), but no immediate death as with oxygen.
History of Discovery
1772: First isolation by Daniel Rutherford Nitrogen gas was first isolated by Daniel Rutherford, a Scottish scientist, who called it "noxious air" due to its inability to support combustion.
1790: Recognition of its inert nature The British scientist Henry Cavendish also contributed to the characterization of nitrogen by studying its role in respiration and its non-reactivity with oxygen.
Atomic Structure
Constitution: The nitrogen atom has 7 protons, 7 neutrons, and 7 electrons, with an electron configuration of 1s² 2s² 2p³. Isotopes:
Nitrogen-14 (¹⁴N): stable isotope, representing 99.63% of natural nitrogen.
Nitrogen-15 (¹⁵N): stable isotope, used in scientific research, particularly in biology and geochemistry.
Physical Properties
Diatomic gas (N₂), colorless, odorless, tasteless.
Molar mass: ≈ 28.014 g/mol
Melting point: 63.15 K (−210.00 °C)
Boiling point: 77.36 K (−195.79 °C)
Density: ~1.2506 g/L (at 0°C and 1 atm)
Inert at room temperature, does not easily interact with other gases or elements.
Chemical Reactivity
Inert gas (very low reactivity) in molecular form N₂.
React under extreme conditions (high temperature, pressure) with hydrogen to form ammonia (NH₃) via the Haber-Bosch process.
Forms nitrogen oxides (NO, NO₂) by reacting with oxygen in the atmosphere.
Involved in biological nitrogen fixation, essential for protein production in plants.
Industrial and Technological Applications
Synthesis of ammonia (NH₃) for fertilizer production (Haber-Bosch process).
Production of nitrates used in explosives and chemical materials.
Use in electronic circuits and cryogenics due to its inert properties.
Liquid nitrogen used as a coolant in various cryogenic applications.
Key role in semiconductor manufacturing and the production of greenhouse gases (NOx).
Biological and Ecological Role
Nitrogen fixation: natural process allowing plants to assimilate nitrogen from the air as nitrates through symbiotic bacteria.
The nitrogen cycle: essential biogeochemical process for plant growth and protein production.
Presence in DNA and amino acids, basic elements of living organisms.
Use of nitrogen for the synthesis of hydrazine, used in certain medications and chemicals.
Environmental and Industrial Challenges
Air pollution problems due to nitrogen oxides (NOx), major contributors to tropospheric ozone formation.
Contribution to the greenhouse effect and acid rain through nitrogen dioxide (NO₂) emissions.
Excessive use of nitrogen fertilizers in agriculture, leading to soil and water pollution.
