Schematic representation of the nitrogen cycle. Abiotic nitrogen fixation has been omitted.
Structure of the FeMo cofactor showing the sites of binding to nitrogenase (the amino acids cys and his).
Ball-and-stick model of the diamminesilver(I) cation, [Ag(NH3)2]+
Nodules are visible on this broad bean root
Figure 1: Nitrogenase with key catalytic sites highlighted. There are two sets of catalytic sites within each nitrogenase enzyme.
Ball-and-stick model of the tetraamminediaquacopper(II) cation, [Cu(NH3)4(H2O)2](2+)
A sectioned alder tree root nodule
Figure 2: Nitrogenase with one set of metal clusters magnified. Electrons travel from the Fe-S cluster (yellow) to the P cluster (red), and end at the FeMo-co (orange).
Jabir ibn Hayyan
Equipment for a study of nitrogen fixation by alpha rays (Fixed Nitrogen Research Laboratory, 1926)
Figure 3: Key catalytic sites within nitrogenase. Atoms are colored by element. Top: Fe-S Cluster Middle: P Cluster Bottom: FeMo-co
This high-pressure reactor was built in 1921 by BASF in Ludwigshafen and was re-erected on the premises of the University of Karlsruhe in Germany.
Lightning heats the air around it breaking the bonds of starting the formation of nitrous acid.
Figure 4: Lowe-Thorneley kinetic model for reduction of nitrogen to ammonia by nitrogenase.
A train carrying Anhydrous Ammonia.
Figure 5: Distal vs. alternating mechanistic pathways for nitrogen fixation in nitrogenase.
Liquid ammonia bottle
Figure 6: Amino acid residues of nitrogenase that interact with MgATP during catalysis.
Household ammonia
Ammoniacal Gas Engine Streetcar in New Orleans drawn by Alfred Waud in 1871.
The X-15 aircraft used ammonia as one component fuel of its rocket engine
Anti-meth sign on tank of anhydrous ammonia, Otley, Iowa. Anhydrous ammonia is a common farm fertilizer that is also a critical ingredient in making methamphetamine. In 2005, Iowa used grant money to give out thousands of locks to prevent criminals from getting into the tanks.
The world's longest ammonia pipeline (roughly 2400 km long), running from the TogliattiAzot plant in Russia to Odessa in Ukraine
Hydrochloric acid sample releasing HCl fumes, which are reacting with ammonia fumes to produce a white smoke of ammonium chloride.
Production trend of ammonia between 1947 and 2007
Main symptoms of hyperammonemia (ammonia reaching toxic concentrations).
Ammonia occurs in the atmospheres of the outer giant planets such as Jupiter (0.026% ammonia), Saturn (0.012% ammonia), and in the atmospheres and ices of Uranus and Neptune.

Nitrogen fixation is a chemical process by which molecular nitrogen, with a strong triple covalent bond, in the air is converted into ammonia or related nitrogenous compounds, typically in soil or aquatic systems but also in industry.

- Nitrogen fixation

These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3).

- Nitrogenase

Biological nitrogen fixation or diazotrophy is an important microbially mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the nitrogenase protein complex (Nif).

- Nitrogen fixation

Nitrogenases are the only family of enzymes known to catalyze this reaction, which is a key step in the process of nitrogen fixation.

- Nitrogenase

Therefore, nitrogen fixation is required for the synthesis of amino acids, which are the building blocks of protein.

- Ammonia

In certain organisms, ammonia is produced from atmospheric nitrogen by enzymes called nitrogenases.

- Ammonia
Schematic representation of the nitrogen cycle. Abiotic nitrogen fixation has been omitted.

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Daniel Rutherford, discoverer of nitrogen


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Chemical element with the symbol N and atomic number 7.

Chemical element with the symbol N and atomic number 7.

Daniel Rutherford, discoverer of nitrogen
The shapes of the five orbitals occupied in nitrogen. The two colours show the phase or sign of the wave function in each region. From left to right: 1s, 2s (cutaway to show internal structure), 2px, 2py, 2pz.
Table of nuclides (Segrè chart) from carbon to fluorine (including nitrogen). Orange indicates proton emission (nuclides outside the proton drip line); pink for positron emission (inverse beta decay); black for stable nuclides; blue for electron emission (beta decay); and violet for neutron emission (nuclides outside the neutron drip line). Proton number increases going up the vertical axis and neutron number going to the right on the horizontal axis.
Molecular orbital diagram of dinitrogen molecule, N2. There are five bonding orbitals and two antibonding orbitals (marked with an asterisk; orbitals involving the inner 1s electrons not shown), giving a total bond order of three.
Solid nitrogen on the plains of Sputnik Planitia on Pluto next to water ice mountains
Structure of [Ru(NH3)5(N2)]2+ (pentaamine(dinitrogen)ruthenium(II)), the first dinitrogen complex to be discovered
Mesomeric structures of borazine, (–BH–NH–)3
Standard reduction potentials for nitrogen-containing species. Top diagram shows potentials at pH 0; bottom diagram shows potentials at pH 14.
Nitrogen trichloride
Nitrogen dioxide at −196 °C, 0 °C, 23 °C, 35 °C, and 50 °C. converts to colourless dinitrogen tetroxide at low temperatures, and reverts to  at higher temperatures.
Fuming nitric acid contaminated with yellow nitrogen dioxide
Schematic representation of the flow of nitrogen compounds through a land environment
A container vehicle carrying liquid nitrogen.

Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen.

Nitrogen fixation by industrial processes like the Frank–Caro process (1895–1899) and Haber–Bosch process (1908–1913) eased this shortage of nitrogen compounds, to the extent that half of global food production (see Applications) now relies on synthetic nitrogen fertilisers.

These complexes, in which a nitrogen molecule donates at least one lone pair of electrons to a central metal cation, illustrate how N2 might bind to the metal(s) in nitrogenase and the catalyst for the Haber process: these processes involving dinitrogen activation are vitally important in biology and in the production of fertilisers.