Editing Nitrogen (section)

===Oxides===
{{main|Nitrogen oxide}}
[[File:Nitrogen dioxide at different temperatures.jpg|thumb|upright=1.36|right|Nitrogen dioxide at −196&nbsp;°C, 0&nbsp;°C, 23&nbsp;°C, 35&nbsp;°C, and 50&nbsp;°C. {{chem|NO|2}} converts to colourless dinitrogen tetroxide ({{chem|N|2|O|4}}) at low temperatures, and reverts to {{chem|NO|2}} at higher temperatures.]]
Nitrogen forms nine molecular oxides, some of which were the first gases to be identified: N<sub>2</sub>O ([[nitrous oxide]]), NO ([[nitric oxide]]), N<sub>2</sub>O<sub>3</sub> ([[dinitrogen trioxide]]), NO<sub>2</sub> ([[nitrogen dioxide]]), N<sub>2</sub>O<sub>4</sub> ([[dinitrogen tetroxide]]), N<sub>2</sub>O<sub>5</sub> ([[dinitrogen pentoxide]]), N<sub>4</sub>O ([[nitrosylazide]]),<ref name="Greenwood443">Greenwood and Earnshaw, pp. 443–58</ref> and N(NO<sub>2</sub>)<sub>3</sub> ([[trinitramide]]).<ref>{{cite journal |last1=Rahm |first1=Martin |last2=Dvinskikh |first2=Sergey V. |last3=Furó |first3=István |last4=Brinck |first4=Tore |date=23 December 2010 |title=Experimental Detection of Trinitramide, N(NO<sub>2</sub>)<sub>3</sub> |journal=Angewandte Chemie International Edition |volume=50 |issue=5 |pages=1145–48 |doi=10.1002/anie.201007047|pmid=21268214 |s2cid=32952729 }}</ref> All are thermally unstable towards decomposition to their elements. One other possible oxide that has not yet been synthesised is [[oxatetrazole]] (N<sub>4</sub>O), an aromatic ring.<ref name="Greenwood443" />

Nitrous oxide (N<sub>2</sub>O), better known as laughing gas, is made by thermal decomposition of molten [[ammonium nitrate]] at 250&nbsp;°C. This is a redox reaction and thus nitric oxide and nitrogen are also produced as byproducts. It is mostly used as a propellant and aerating agent for [[cream|sprayed canned whipped cream]], and was formerly commonly used as an anaesthetic. Despite appearances, it cannot be considered to be the [[inorganic anhydride|anhydride]] of [[hyponitrous acid]] (H<sub>2</sub>N<sub>2</sub>O<sub>2</sub>) because that acid is not produced by the dissolution of nitrous oxide in water. It is rather unreactive (not reacting with the halogens, the alkali metals, or [[ozone]] at room temperature, although reactivity increases upon heating) and has the unsymmetrical structure N–N–O (N≡N<sup>+</sup>O<sup>−</sup>↔<sup>−</sup>N=N<sup>+</sup>=O): above 600&nbsp;°C it dissociates by breaking the weaker N–O bond.<ref name="Greenwood443" />
Nitric oxide (NO) is the simplest stable molecule with an odd number of electrons. In mammals, including humans, it is an important cellular [[signalling molecule]] involved in many physiological and pathological processes.<ref>{{cite journal|pmid=10390607|year=1999|last1=Hou|first1=Y. C.|last2=Janczuk|first2=A.|last3=Wang|first3=P. G.|title=Current trends in the development of nitric oxide donors|volume=5|issue=6|pages=417–41|journal=Current Pharmaceutical Design|doi=10.2174/138161280506230110111042 }}</ref> It is formed by catalytic oxidation of ammonia. It is a colourless paramagnetic gas that, being thermodynamically unstable, decomposes to nitrogen and oxygen gas at 1100–1200&nbsp;°C. Its bonding is similar to that in nitrogen, but one extra electron is added to a ''π''* antibonding orbital and thus the bond order has been reduced to approximately 2.5; hence dimerisation to O=N–N=O is unfavourable except below the boiling point (where the ''cis'' isomer is more stable) because it does not actually increase the total bond order and because the unpaired electron is delocalised across the NO molecule, granting it stability. There is also evidence for the asymmetric red dimer O=N–O=N when nitric oxide is condensed with polar molecules. It reacts with oxygen to give brown nitrogen dioxide and with halogens to give nitrosyl halides. It also reacts with transition metal compounds to give nitrosyl complexes, most of which are deeply coloured.<ref name="Greenwood443" />

Blue dinitrogen trioxide (N<sub>2</sub>O<sub>3</sub>) is only available as a solid because it rapidly dissociates above its melting point to give nitric oxide, nitrogen dioxide (NO<sub>2</sub>), and dinitrogen tetroxide (N<sub>2</sub>O<sub>4</sub>). The latter two compounds are somewhat difficult to study individually because of the equilibrium between them, although sometimes dinitrogen tetroxide can react by heterolytic fission to [[nitrosonium]] and [[nitrate]] in a medium with high dielectric constant. Nitrogen dioxide is an acrid, corrosive brown gas. Both compounds may be easily prepared by decomposing a dry metal nitrate. Both react with water to form [[nitric acid]]. Dinitrogen tetroxide is very useful for the preparation of anhydrous metal nitrates and nitrato complexes, and it became the storable oxidiser of choice for many rockets in both the United States and [[USSR]] by the late 1950s. This is because it is a [[hypergolic propellant]] in combination with a [[hydrazine]]-based [[Rocket propellant|rocket fuel]] and can be easily stored since it is liquid at room temperature.<ref name="Greenwood443" />

The thermally unstable and very reactive dinitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) is the anhydride of [[nitric acid]], and can be made from it by dehydration with [[phosphorus pentoxide]]. It is of interest for the preparation of explosives.<ref>{{cite journal|author=Talawar, M. B.|title=Establishment of Process Technology for the Manufacture of Dinitrogen Pentoxide and its Utility for the Synthesis of Most Powerful Explosive of Today – CL-20|journal=Journal of Hazardous Materials|year= 2005| volume =124|issue=1–3| pages =153–64|doi=10.1016/j.jhazmat.2005.04.021|pmid=15979786|bibcode=2005JHzM..124..153T |display-authors=etal}}</ref> It is a [[deliquescent]], colourless crystalline solid that is sensitive to light. In the solid state it is ionic with structure [NO<sub>2</sub>]<sup>+</sup>[NO<sub>3</sub>]<sup>−</sup>; as a gas and in solution it is molecular O<sub>2</sub>N–O–NO<sub>2</sub>. Hydration to nitric acid comes readily, as does analogous reaction with [[hydrogen peroxide]] giving [[peroxonitric acid]] (HOONO<sub>2</sub>). It is a violent oxidising agent. Gaseous dinitrogen pentoxide decomposes as follows:<ref name="Greenwood443" />
:N<sub>2</sub>O<sub>5</sub> {{eqm}} NO<sub>2</sub> + NO<sub>3</sub> → NO<sub>2</sub> + O<sub>2</sub> + NO
:N<sub>2</sub>O<sub>5</sub> + NO {{eqm}} 3 NO<sub>2</sub>