Nitrogen: the essentials
Nitrogen is a Group 15 element. Nitrogen makes up about 78% of the atmosphere by volume but the atmosphere of Mars contains less than 3% nitrogen. The element seemed so inert that Lavoisier named it azote, meaning "without life". However, its compounds are vital components of foods, fertilizers, and explosives. Nitrogen gas is colourless, odourless, and generally inert. As a liquid it is also colourless and odourless.
When nitrogen is heated, it combines directly with magnesium, lithium, or calcium. When mixed with oxygen and subjected to electric sparks, it forms nitric oxide (NO) and then the dioxide (NO2). When heated under pressure with hydrogen in the presence of a suitable catalyst , ammonia forms (Haber process). Nitrogen is "fixed" from the atmosphere by bacteria in the roots of certain plants such as clover. Hence the usefulness of clover in crop rotation.
Image adapted with permission from Prof James Marshall's (U. North Texas, USA) Walking Tour of the elements CD.
Nitrogen: historical information
It was known during the 18th century that air contains at least two gases, one of which supports combustion and life, and the other of which does not. Nitrogen was discovered by Daniel Rutherford in 1772, who called it noxious air, but Scheele, Cavendish, Priestley, and others at about the same time studied "burnt" or "dephlogisticated" air, as air without oxygen was then called.
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for nitrogen is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Nitrogen around us Read more »
Nitrogen is a key component of biological molecules such as proteins (which are made from amino acids, and nucleic acids. The nitrogen cycle in nature is very important.
Nitrogen gas (dinitrogen, N2) makes up about 78% of the atmosphere by volume. The atmosphere of Mars contains less than 3% nitrogen. There are relatively few minerals containing nitrogen but nitrates such as "saltpetre" (NaNO3) are very important.
|Location||ppb by weight||ppb by atoms||Links|
|Human||26000000 ppb by weight||12000000 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 63.05 [‑210.1 °C (‑346.18 °F)] K
- Boiling point: 77.36 [‑195.79 °C (‑320.42 °F)] K
- Enthalpy of fusion: 0.36 (per mol N atoms) kJ mol-1
Crystal structure Read more »
The solid state structure of nitrogen is: hcp (hexagonal close-packed).
Nitrogen: orbital properties Read more »
Nitrogen atoms have 7 electrons and the shell structure is 2.5. The ground state electronic configuration of neutral Nitrogen is [He].2s2.2p3 and the term symbol of Nitrogen is 4S3/2.
- Pauling electronegativity: 3.04 (Pauling units)
- First ionisation energy: 1402.3 kJ mol‑1
- Second ionisation energy: 2856 kJ mol‑1
Isolation: there is never any need to make nitrogen in the laboratory as it is readily available commercially or through in-house air liquefaction plants. However the decomposition of sodium azide is one route to N2 and decomposition is ammonium dichromate is another. Both reactions must only be carried out under controlled conditions by a professional.
NaN3 (300°C) → 2Na + 3N2
(NH4)2Cr2O7 → N2 + Cr2O3 + 4H2O
Nitrogen is made on massive scale by liquefaction of air and fractional distillation of the resulting liquid air to separate out oxygen and other gases. Very high purity nitrogen is available by this route.
Nitrogen isotopes Read more »
Nitrogen has two isotopes, N-14 and N-15, both of which are used in various applications. N-15 is used for the production of the radioisotope O-15 which is used in PET. N-15 is also used to study the uptake of Nitrogen in plants and the metabolism of proteins in the human body. N-14 is used for the production of the PET radioisotope C-11. It can also be used for the production of the PET radioisotopes N-13 and O-15.
|14N||14.003 074 005 2(9)||99.632 (7)||1||0.4037607|
|15N||15.000 108 898 4(9)||0.368 (7)||1/2||-0.2831892|