编辑“︁氮”︁（章节）

== 性质 ==
[[File:Neon orbitals.png|thumb|upright=1.6|right|图为氮的五个电子轨道，不同颜色区别波函数的不同相位。从左到右分别是：1s、2s（已切开来显示内部构造）、2p<sub>''x''</sub>、2p<sub>''y''</sub>、2p<sub>''z''</sub>轨道。]]

一个氮原子有七粒电子。在基态下，这些电子的[[电子排布]]为1s{{su|p=2}}2s{{su|p=2}}2p{{su|p=1|b=''x''}}2p{{su|p=1|b=''y''}}2p{{su|p=1|b=''z''}}。它的2s和2p轨道有五个[[价电子]]，其中位于2p轨道的三个并未成对。氮的[[电负性]]是所有元素第四大的，鲍林标度为3.04，位列[[氯]]（3.16）、[[氧]]（3.44）和[[氟]]（3.98）之下。（更轻的[[惰性气体]][[氦]]、[[氖]]、[[氩]]的电负性很可能比氮高，而在阿莱标度下正是如此。）{{sfn|Greenwood|Earnshaw|1997|pp=411–12}}氮的单键[[共价半径]]为71&nbsp;pm，比[[硼]]（84&nbsp;pm）和[[碳]]（76&nbsp;pm）小，而比氧（66&nbsp;pm）和氟（57&nbsp;pm）大，符合元素周期律。[[氮离子]]（N<sup>3−</sup>）则要大得多，离子半径为146&nbsp;pm，与[[氧离子]]（O<sup>2−</sup>，140&nbsp;pm）和[[氟离子]]（F<sup>−</sup>，133&nbsp;pm）相似。{{sfn|Greenwood|Earnshaw|1997|pp=411–12}}氮的前三级电离能分别是1.402&nbsp;MJ·mol<sup>−1</sup>、2.856&nbsp;MJ·mol<sup>−1</sup>、4.577&nbsp;MJ·mol<sup>−1</sup>，这样高的电离能使氮无法在化学反应中生成简单阳离子。{{sfn|Greenwood|Earnshaw|1997|p=550}}2p轨道的性质使得氮、氧、氟和下面的元素相比有异常的性质。2p轨道很小，半径和2s轨道相似，因此容易与它[[杂化]]。此外，原子核和2s、2p轨道的价电子产生的吸引力极大，导致氮极高的电负性。出于同样的原因，氮几乎没有[[超价分子]]，因为氮极高的电负性将会强烈吸引电子，难以成为富含电子的[[三中心四电子键]]的中心原子。因此，虽然氮位于氮族元素，但化学性质和更重的氮族元素[[磷]]、[[砷]]、[[锑]]、[[铋]]有显著区别。<ref name="Kaupp">{{cite journal |last=Kaupp |first=Martin |date=1 December 2006 |title=The role of radial nodes of atomic orbitals for chemical bonding and the periodic table |journal=Journal of Computational Chemistry |volume=28 |issue=1 |pages=320–25 |doi=10.1002/jcc.20522 |pmid=17143872 |s2cid=12677737 |doi-access=free }}</ref>

氮不像碳那样容易[[成链]]，但和碳一样可以和金属形成化合物。氮也可以[[碳的氮化物|和碳形成化合物]]，它们的结构各不相同，有链形的、[[石墨]]形的、以及[[富勒烯]]形的。<ref>{{cite journal |last1=Miller |first1=T. S. |last2=Belen |first2= A.|last3= Suter|first3= T. M.|last4= Sella|first4= A.|last5= Corà|first5= A.|last6= McMillan|first6= P. F.|date=2017 |title= Carbon nitrides: synthesis and characterization of a new class of functional materials |journal=Physical Chemistry Chemical Physics |volume= 19|issue= 24|pages=15613–15638 |doi=10.1039/C7CP02711G|pmid=28594419 |bibcode=2017PCCP...1915613M |doi-access= free}}</ref>

氮和氧一样电负性很高，可以形成[[氢键]]，也能通过分享[[孤电子对]]来形成[[配合物]]。氨（NH<sub>3</sub>）和水（H<sub>2</sub>O）的化学性质有些相似，例如都可以接受氢离子，分别生成NH<sub>4</sub><sup>+</sup>和H<sub>3</sub>O<sup>+</sup>；或是释放氢离子，分别生成NH<sub>2</sub><sup>−</sup>和OH<sup>−</sup>。这四种离子都能产生固体化合物。<ref>{{cite book |last1= House|first1=J. E. |last2=House |first2= K. A.|date=2016 |title=Descriptive Inorganic Chemistry |location= Amsterdam|publisher= Elsevier|page= 198|isbn=978-0-12-804697-5 }}</ref>

和隔壁的碳和氧一样，氮倾向于与其它碳、氮、氧原子形成多重键。{{sfn|Greenwood|Earnshaw|1997|pp=412–16}}由于更重的氮族元素都较难形成多重键，所以氮可以形成的[[氮氧化物]]、[[亚硝酸盐]]、[[硝酸盐]]、[[硝基化合物]]、[[亚硝基化合物]]、[[偶氮化合物]]、[[重氮化合物]]、[[叠氮化合物]]、[[氰酸盐]]、[[硫氰酸盐]]、[[亚胺]]都难以找到对应的更重氮族元素化合物；反过来说磷能形成各种复杂的含氧酸，但氮不能。{{sfn|Greenwood|Earnshaw|1997|pp=412–16}}

=== 同位素 ===
{{main|氮的同位素}}
已发现的氮的[[同位素]]共有十七种，包括<chem>^10N</chem>至<chem>^25N</chem>，其中只有<chem>^14N</chem>和<chem>^15N</chem>是最稳定的。最常见的是<chem>^14N</chem>（99.634%），是在[[恒星]]的[[碳氮氧循環]]过程中产生的。<ref name="BetheBible">{{cite journal
 |last=Bethe |first=H. A.
 |year=1939
 |title=Energy Production in Stars
 |url=https://archive.org/details/sim_physical-review_1939-03-01_55_5/page/n9 |journal=[[Physical Review]]
 |volume=55 |issue=5 |pages=434–56
 |bibcode=1939PhRv...55..434B
 |doi= 10.1103/PhysRev.55.434
}}</ref>在其他人工合成的同位素中，<chem>^13N</chem>的半衰期是10分钟，其他的同位素的半衰期都是以秒计或更短。<ref name="NUBASE">{{cite journal|author=Audi, G.; Wapstra, A. H.; Thibault, C.; Blachot, J. and Bersillon, O. |year=2003 |title=The NUBASE evaluation of nuclear and decay properties |url=http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf |journal=[[Nuclear Physics A]] |volume=729 |issue= |pages=3–128 |doi=10.1016/j.nuclphysa.2003.11.001 |bibcode=2003NuPhA.729....3A |deadurl=yes |archiveurl=https://web.archive.org/web/20080923135135/http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf |archivedate=2008-09-23 }}</ref>

生物介导反应（例如[[同化 (生物学)|同化]]，[[硝化反应]]和[[反硝化反应]]）牢牢地控制着土壤的氮动力学。这些反应一般会导致基质的<chem>^15N</chem>富集和产物的<chem>^15N</chem>消耗。<ref name="enrich">{{cite book | url = http://books.google.de/books?id=U9y3whFC2DIC&pg=PA74 | pages = 74–75 | title = Stable Isotopes and Biosphere - Atmosphere Interactions: Processes and Biological Controls | isbn = 9780080525280 | author1 = Flanagan | first1 = Lawrence B. | last2 = Ehleringer | first2 = James R | last3 = Pataki | first3 = Diane E. | date = 2004-12-15 | access-date = 2013-10-02 | archive-date = 2017-01-09 | archive-url = https://web.archive.org/web/20170109022507/https://books.google.de/books?id=U9y3whFC2DIC&pg=PA74 | dead-url = no }}</ref>

地球大气中的氮气的一小部分（0.73%）是{{Link-en|同位素体|isotopologue}}<chem>^14N</chem><chem>^15N</chem>，其余的大部分是<chem>^14N2</chem>。<ref>{{cite web | url = http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=N | title = Atomic Weights and Isotopic Compositions for Nitrogen | publisher = NIST | accessdate = 2013-05-22 | archive-date = 2013-03-02 | archive-url = https://web.archive.org/web/20130302103202/http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=N | dead-url = no }}</ref>

===同素异形体===
{{main|氮的同素异形体}}
单原子氮是非常活泼的三[[自由基]]，有三个不成对电子。它极易和其它元素反应，生成氮化物。两个单原子氮之间的碰撞会产生激发态的N<sub>2</sub>分子，后者的能量之高甚至可以把稳定的[[二氧化碳]]和[[水]]撞成自由基。单原子氮可通过对0.1–2&nbsp;mmHg的氮气通电而成，并伴随着桃黄色的光。这种光直到结束通电后几分钟才会缓慢消失。{{sfn|Greenwood|Earnshaw|1997|pp=412–16}}

氮通常以[[氮气|N<sub>2</sub>]]形式存在。它是无色、无臭、无味的[[抗磁性]]气体，熔点−210&nbsp;°C，沸点−196&nbsp;°C。{{sfn|Greenwood|Earnshaw|1997|pp=412–16}}由于N<sub>2</sub>中含有又短（109.76&nbsp;pm）、键能又高（945.41&nbsp;kJ/mol），因此很强的氮氮[[三键]]，它并不活泼，但仍可和金属[[锂]]和某些[[过渡金属]]配合物反应。{{sfn|Greenwood|Earnshaw|1997|pp=412–16}}<ref>{{cite web | url=http://www.uigi.com/nitrogen.html | title=Universal Industrial Gases, Inc...Nitrogen N2 Properties, Uses, Applications - Gas and Liquid | access-date=2013-09-30 | archive-date=2013-09-28 | archive-url=https://web.archive.org/web/20130928194449/http://www.uigi.com/nitrogen.html | dead-url=no }}</ref>

氮还有可能形成[[低聚物]]和聚合物。它们如果真的被合成了，将会是能量密度极高的材料，可用作推进剂或炸药。<ref name="Lewars">{{cite book |title=Modeling Marvels: Computational Anticipation of Novel molecules |last=Lewars |first=Errol G. |year=2008 |publisher=[[Springer Science+Business Media]] |isbn=978-1-4020-6972-7 |doi=10.1007/978-1-4020-6973-4 |pages=141–63 }}</ref>在[[金刚石对顶砧]]产生的110万个[[大气压]]的高压和2000&nbsp;K的高温下，氮会聚合成由单键链接而成的晶体。它的结构与[[钻石]]相似，且都有极强的[[共价键]]，因此别名“氮钻石”。<ref>{{Cite news|url=http://www.physorg.com/news693.html|title=Polymeric nitrogen synthesized|publisher=physorg.com|date=5 August 2004|access-date=2009-06-22|archive-date=2012-01-24|archive-url=https://web.archive.org/web/20120124231419/http://www.physorg.com/news693.html|url-status=live}}</ref>

[[File:Mountainous Shoreline of Sputnik Planum (PIA20198).png|thumb|right|upright=1.1|[[冥王星]][[史波尼克高原]]（图片右下方）的{{le|固态氮|Solid nitrogen}}]]
在常压下，N<sub>2</sub>会在{{convert|77|K|C}}下[[液化]]，在{{convert|63|K|C}}下[[凝固]]成[[六方晶系]]的β相，<ref name="Gray">{{cite book|last=Gray|first=Theodore|title=The Elements: A Visual Exploration of Every Known Atom in the Universe|date=2009|publisher=Black Dog & Leventhal Publishers|location=New York|isbn=978-1-57912-814-2}}</ref>而继续降温到{{convert|35.4|K|C}}则会使N<sub>2</sub>变成[[立方晶系]]的α相。<ref name="schu">{{cite journal|last1=Schuch|first1=A. F.|last2=Mills|first2=R. L.|title=Crystal Structures of the Three Modifications of Nitrogen 14 and Nitrogen 15 at High Pressure|journal=The Journal of Chemical Physics|date=1970|volume=52|issue=12|pages=6000–08|doi=10.1063/1.1672899|bibcode=1970JChPh..52.6000S}}</ref>[[液氮]]和水一样是无色液体，但其密度（0.808&nbsp;g/mL）只有水的80.8%，是常用的[[制冷剂]]。<ref>{{Cite journal | last1 = Iancu | first1 = C. V. | last2 = Wright | first2 = E. R. | last3 = Heymann | first3 = J. B. | last4 = Jensen | first4 = G. J. | title = A comparison of liquid nitrogen and liquid helium as cryogens for electron cryotomography | doi = 10.1016/j.jsb.2005.12.004 | journal = Journal of Structural Biology | volume = 153 | issue = 3 | pages = 231–40 | year = 2006 | pmid = 16427786}}</ref>{{le|固态氮|Solid nitrogen}}有多种晶体结构，是冥王星<ref>{{cite news|title=Flowing nitrogen ice glaciers seen on surface of Pluto after New Horizons flyby|url=http://www.abc.net.au/news/2015-07-25/flowing-nitrogen-ice-glaciers-seen-on-surface-of-pluto/6647636|newspaper=ABC News|access-date=6 October 2015|date=25 July 2015|archive-date=29 September 2015|archive-url=https://web.archive.org/web/20150929044226/http://www.abc.net.au/news/2015-07-25/flowing-nitrogen-ice-glaciers-seen-on-surface-of-pluto/6647636|url-status=live}}</ref>和[[海卫一]]<ref>{{cite encyclopedia|title = Encyclopedia of the Solar System "Triton"|last1 = McKinnon|first1 = William B.|last2 = Kirk|first2 = Randolph L.|publisher = [[Elsevier]]|date = 2014|editor1-first = Tilman|editor1-last = Spohn|editor2-first = Doris|editor2-last = Breuer|editor3-first = Torrence|editor3-last = Johnson|edition = 3rd|location = Amsterdam; Boston|isbn = 978-0-12-416034-7|pages = 861–82|url = https://books.google.com/books?id=0bEMAwAAQBAJ&pg=PA861|access-date = 2016-04-30|archive-date = 2016-09-03|archive-url = https://web.archive.org/web/20160903233037/https://books.google.com/books?id=0bEMAwAAQBAJ&pg=PA861|url-status = live}}</ref>表面的主要成分。即使在那边的低温下，这些固态氮仍具有挥发性，容易[[升华]]，形成氮气。这些氮气有的形成大气层，有的形成[[霜]]。在海卫一的极地冰盖，还会有氮气组成的[[间歇泉]]。<ref>{{cite web |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Triton |publisher=[[NASA]] |access-date=September 21, 2007 |title=Neptune: Moons: Triton |archive-url=https://web.archive.org/web/20111015074425/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Triton |archive-date=October 15, 2011 |url-status=dead }}</ref>

2025年6月，[[苏州大学]]校友，德国[[吉森大学]]博士生钱伟煜(Weiyu Qian)等人在[[Nature]]上发文,宣布发现了氮的新一种同素异形体：“六氮”(hexanitrogen) N₆分子<ref>{{Cite journal |last=Qian |first=Weiyu |last2=Mardyukov |first2=Artur |last3=Schreiner |first3=Peter R. |title=Preparation of a neutral nitrogen allotrope hexanitrogen C2h-N6 |url=https://www.nature.com/articles/s41586-025-09032-9 |journal=Nature |language=en |date=2025-06 |volume=642 |issue=8067 |doi=10.1038/s41586-025-09032-9 |issn=1476-4687 |pmc=12158757 |pmid=40500322 |access-date=2025-12-31}}</ref> 。该分子可以视为[[叠氮根]] N₃⁻的二聚单质状态，并且可以与[[拟卤素]]类比。