编辑“︁碘”︁

{{NoteTA
|G1 = Chemistry
}}
{{Elementbox
|number=53 
|symbol=I
|name=碘
|enname=Iodine
|left=[[碲]] 
|right=[[氙]] 
|above=[[溴]] 
|below=[[砹]] 
|series= 卤素
|group=17 
|period=5 
|block=p 
|series color=ffff99
|phase color=
|image name= Sample of iodine.jpg
|appearance=带金属光泽的紫灰色，蒸汽为紫色
|atomic mass= 126.90447(3){{CIAAW2021}}
|electron configuration= &#91;[[氪|Kr]]&#93; 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>5</sup>
|electrons per shell=2, 8, 18, 18, 7
|electron shell image=Electron shell 053 Iodine (diatomic nonmetal) - no label.svg
|color=
|phase=固态
|density gpcm3nrt= 4.933
|melting point K=386.85
|melting point C=113.7
|melting point F=236.66
|boiling point K=457.4
|boiling point C=184.3
|boiling point F=363.7
|triple point K=386.65
|triple point kPa=12.1
|critical point K=819
|critical point MPa=11.7
|heat fusion=（I<sub>2</sub>）15.52
|heat vaporization=（I<sub>2</sub>）41.57
|heat capacity=（I<sub>2</sub>）54.44
|vapor pressure 1= 260
|vapor pressure 10= 282
|vapor pressure 100= 309
|vapor pressure 1 k= 342
|vapor pressure 10 k= 381
|vapor pressure 100 k= 457
|vapor pressure comment=
|crystal structure= 正交
|oxidation states= '''-1'''、'''+1'''、+2<ref>I(II)存在于一氧化碘（IO）中，参见{{cite journal|last1=Nikitin|first1=I V|title=Halogen monoxides|journal=Russian Chemical Reviews|date=31 August 2008|volume=77|issue=8|pages=739–749|doi=10.1070/RC2008v077n08ABEH003788|bibcode=2008RuCRv..77..739N}}</ref>、'''+3'''、+4<ref>I(IV)存在于[[碘的氧化物|二氧化碘]]（IO<sub>2</sub>）中，参见{{cite book|publisher= Dover Publications, Inc.|year= 1988|edition= 3rd|page= [https://archive.org/details/generalchemistry00paul_0/page/259 259]|isbn= 978-0-486-65622-9|title= General Chemistry|url= https://archive.org/details/generalchemistry00paul_0|first= Linus|last= Pauling|chapter= Oxygen Compounds of Nonmetallic Elements}}</ref>、'''+5'''、+6<ref>I(VI)存在于IO<sub>3</sub>、IO<sub>4</sub><sup>2−</sup>、H<sub>5</sub>IO<sub>6</sub><sup>−</sup>、H<sub>2</sub>IO<sub>5</sub><sup>2−</sup>、H<sub>4</sub>IO<sub>6</sub><sup>2−</sup>和HIO<sub>5</sub><sup>3−</sup>中，参见{{cite journal|doi=10.1039/F19817701707|title=Laser flash photolysis and pulse radiolysis of iodate and periodate in aqueous solution. Properties of iodine(VI)|year=1981|last1=Kläning|first1=Ulrik K.|last2=Sehested|first2=Knud|last3=Wolff|first3=Thomas|journal=J. Chem. Soc., Faraday Trans. 1|volume=77|issue=7|pages=1707–18}}</ref>、'''+7'''<br />（强[[酸性]]氧化物）
|electronegativity= 2.66
|number of ionization energies=3
|1st ionization energy= 1008.4
|2nd ionization energy= 1845.9
|3rd ionization energy= 3180
|electron affinity=295.15
|atomic radius= 140
|covalent radius= 139±3
|Van der Waals radius= 198
|magnetic ordering= [[抗磁性]]<ref>[http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elementmagn.pdf Magnetic susceptibility of the elements and inorganic compounds] {{Wayback|url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elementmagn.pdf |date=20110303222309 }}, in Handbook of Chemistry and Physics 81st edition, CRC press.</ref>
|magnetic susceptibility= {{val|−88.7|e=−6}}&#x20;（298&nbsp;K）<ref>{{Cite book|title=CRC, [[CRC化学和物理手册|Handbook of Chemistry and Physics]]|last=Weast|first=Robert|publisher=Chemical Rubber Company Publishing|year=1984|isbn=0-8493-0464-4|location=Boca Raton, Florida|pages=E110}}</ref>
|electrical resistivity at 0= 1.3×10<sup>7</sup>
|thermal conductivity= 0.449
|Bulk modulus= 7.7
|CAS number= 7553-56-2
|isotopes= {{infobox iodine isotopes}}
|discovered by=[[贝尔纳·库尔图瓦]]
|discovery date=1811
|first isolation by=贝尔纳·库尔图瓦
|first isolation date=1811
}}

'''{{zy|碘|diǎn|ㄉㄧㄢˇ|din2}}'''（{{langx|en|Iodine}}；源于{{langx|el|ἰώδης|Iódis|深紫羅蘭色}}）是一種[[化學元素]]，其[[化學符號]]为'''{{化學式|碘}}'''，[[原子序數]]为53。碘是最重的穩定[[鹵素]]，在[[標準狀況]]下為有光澤的紫黑色固態非金屬，在{{convert|114|C}}時融化成深紫色液體，在{{convert|184|C}}時气化成紫色氣體。碘元素在1811年由[[法國]]化學家[[贝尔纳·库尔图瓦]]發現，兩年後[[約瑟夫·路易·盖-呂薩克]]因碘蒸汽的颜色而以[[希臘語]] ἰώδης （深紫羅蘭色）命名碘為「iodine」。

碘有許多[[氧化態]]，包括[[碘化物]]（I<sup>-</sup>）的-1、[[碘酸盐]]（IO<sub>3</sub><sup>-</sup>）的+5和[[高碘酸盐]]的+7。碘是[[元素豐度|豐度]]最低的非人造鹵素，在地殼中豐度排名第61。碘亦是人體必需的元素中[[原子序]]最大的，是合成[[甲狀腺素]]的必要成分<ref name="lpi">{{cite web|url=http://lpi.oregonstate.edu/mic/minerals/iodine|title=Iodine|publisher=Micronutrient Information Center, Linus Pauling Institute, [[Oregon State University]], Corvallis|date=2015|access-date=20 November 2017|archive-date=2015-04-17|archive-url=https://web.archive.org/web/20150417055246/http://lpi.oregonstate.edu/mic/minerals/iodine|dead-url=no}}</ref>。碘缺乏症是造成[[智能障礙]]的主因，影響了將近二十億人，但可預防。<ref>{{Cite news|url= https://query.nytimes.com/gst/fullpage.html?res=9E05E3D81231F935A25751C1A9609C8B63|work=The New York Times|title=In Raising the World's I.Q., the Secret's in the Salt| vauthors = McNeil Jr DG |date=2006-12-16|access-date=2009-07-21|url-status=live|archive-url= https://web.archive.org/web/20100712011551/http://query.nytimes.com/gst/fullpage.html?res=9E05E3D81231F935A25751C1A9609C8B63|archive-date=2010-07-12}}</ref>

現今生產碘的主要國家是[[智利]]與[[日本]]。因為其高原子量且容易形成[[有機化合物]]，所以可用作無毒的[[造影剂]]。人體吸收碘的專一性也使其放射性同位素用于治療[[甲狀腺癌]]。此外，在工業上製造[[醋酸]]與一些[[聚合物]]時，也會使用碘作為[[催化劑]]。碘是[[世界卫生组织基本药物标准清单|世界卫生组织基本药物]]。<ref name="WHO22nd">{{cite book | vauthors = ((World Health Organization)) | title = World Health Organization model list of essential medicines: 22nd list (2021) | year = 2021 | hdl = 10665/345533 | author-link = World Health Organization | publisher = World Health Organization | location = Geneva | id = WHO/MHP/HPS/EML/2021.02 | hdl-access=free }}</ref>

== 历史 ==
碘是由法国化学家[[貝爾納·庫爾圖瓦]]于1811年發現的。<ref name="court">{{Cite journal| vauthors = Courtois B  |title=Découverte d'une substance nouvelle dans le Vareck |trans-title=Discovery of a new substance in seaweed |journal=Annales de chimie |volume=88 |pages=304–310 |date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=RA2-PA304|language=fr}}</ref><ref>{{Cite journal | vauthors = Swain PA |title=Bernard Courtois (1777–1838) famed for discovering iodine (1811), and his life in Paris from 1798 |journal=Bulletin for the History of Chemistry |volume=30 |issue=2 |page=103 |date=2005 |url=http://www.scs.uiuc.edu/~mainzv/HIST/awards/OPA%20Papers/2007-Swain.pdf |access-date=2 April 2009 |archive-url=https://web.archive.org/web/20100714110757/http://www.scs.uiuc.edu/~mainzv/HIST/awards/OPA%20Papers/2007-Swain.pdf |archive-date=14 July 2010 |url-status=dead }}</ref>当时正值[[拿破仑战争]]，因此[[法国]]的硝石（[[火药]]的必须成分）需求量很高。开采硝石需要[[碳酸钠]]，而后者可以从[[海藻]]中提取。提取这些碳酸钠需要先烧掉海藻，再用水洗灰烬，剩余的废物可用[[硫酸]]销毁。库尔图瓦有一次在销毁过程中加了太多硫酸，结果产生一团紫色气体。他注意到这些气体会在冷的地方结晶，产生深色晶体。{{sfn|Greenwood|Earnshaw|1997|p=794}}库尔图瓦怀疑这种物质是新元素，但因缺少经费而没有进一步研究这种物质。<ref name="vdK">{{cite web |url=http://elements.vanderkrogt.net/element.php?sym=i |title=53 Iodine |publisher=Elements.vanderkrogt.net |access-date=23 October 2016 |archive-date=2010-01-23 |archive-url=https://web.archive.org/web/20100123001444/http://elements.vanderkrogt.net/element.php?sym=I |dead-url=no }}</ref>

于是，库尔图瓦把这种物质给了他的朋友{{le|查尔斯·伯纳德·德索姆|Charles Bernard Desormes}}和{{le|尼古拉斯·克莱门特|Nicolas Clément}}，让他们研究它。他也把这种物质给了[[约瑟夫·路易·盖-吕萨克]]和[[安德烈-马里·安培]]。1813年11月29日，德索姆和克莱门特公开了库尔图瓦的发现，并在[[法兰西学会]]的会议中描述了这种物质。<ref>Gazette nationale ou Le Moniteur Universel在1813年12月2日刊登了他们公告的摘要，参见：
*  {{cite journal |last1=(Staff) |title=Institut Imperial de France |journal=Le Moniteur Universel |date=2 December 1813 |issue=336 |page=1344 |url=https://www.retronews.fr/journal/gazette-nationale-ou-le-moniteur-universel/02-decembre-1813/149/1332251/2 |language=fr|access-date=2022-11-28 |archive-date=2022-11-28 |archive-url=https://web.archive.org/web/20221128171041/https://www.retronews.fr/journal/gazette-nationale-ou-le-moniteur-universel/02-decembre-1813/149/1332251/2 |dead-url=no }}
*  {{cite journal |vauthors=Chattaway FD |title=The discovery of iodine |journal=The Chemical News … |date=23 April 1909 |volume=99 |issue=2578 |pages=193–195 |url=https://books.google.com/books?id=Rco_AQAAIAAJ&pg=PA193 }}</ref>12月6日，盖-吕萨克宣布这种物质是一种元素或是一种[[氧化物]]。<ref name="Gay-Lussac">{{Cite journal | vauthors = Gay-Lussac J |title=Sur un nouvel acide formé avec la substance décourverte par M. Courtois |trans-title=On a new acid formed by the substance discovered by Mr. Courtois |journal=Annales de Chimie |volume=88|pages=311–318|date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=PA311|language=fr}}</ref><ref>{{Cite journal| vauthors = Gay-Lussac J |title=Sur la combination de l'iode avec d'oxigène |trans-title=On the combination of iodine with oxygen |journal=Annales de Chimie |volume=88 |pages=319–321|date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=PA319|language=fr}}</ref><ref>{{Cite journal| vauthors = Gay-Lussac J |title=Mémoire sur l'iode |trans-title=Memoir on iodine |journal=Annales de Chimie |volume=91 |pages=5–160|date=1814 |url=https://books.google.com/books?id=Efms0Fri1CQC&pg=PA5|language=fr}}</ref>他提议把这种物质以碘蒸汽的颜色命名为''iode''（源自[[古希腊语]] {{lang|grc|ἰοειδής}}，意为紫色）。<ref name="court" /><ref name="Gay-Lussac" />安培把他的样本给了[[汉弗里·戴维]]，而戴维注意到了这种物质和[[氯]]相似。<ref>{{Cite journal| vauthors = Davy H |author-link=汉弗里·戴维|title=Sur la nouvelle substance découverte par M. Courtois, dans le sel de Vareck |trans-title=On the new substance discovered by Mr. Courtois in the salt of seaweed |journal=Annales de Chimie |volume=88|pages=322–329 |date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=PA322|language=fr}}</ref>戴维在12月10日写信给[[皇家学会]]，称他确认了一种新元素。<ref>{{Cite journal| vauthors = Davy H |author-link=汉弗里·戴维|title=Some experiments and observations on a new substance which becomes a violet coloured gas by heat |journal=Philosophical Transactions of the Royal Society of London |volume=104 |pages=74–93 |date=1 January 1814 |doi=10.1098/rstl.1814.0007 |doi-access=free }}</ref>戴维和盖-吕萨克就谁最先发现碘是一种元素的问题爆发了争论，但两位科学家都承认库尔图瓦是第一个分离碘的人。<ref name="vdK" />

1873年，法国医学研究员{{le|卡西米·达万尼|Casimir Davaine}}发现碘可以杀菌。<ref>{{cite journal |vauthors=Davaine C |title=Recherches relatives à l'action des substances dites ''antiseptiques'' sur le virus charbonneux |journal=Comptes rendus hebdomadaires des séances de l'Académie des Sciences |date=1873 |volume=77 |pages=821–825 |url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112025711521&view=1up&seq=829 |trans-title=Investigations regarding the action of so-called ''antiseptic'' substances on the anthrax bacterium |language=fr|access-date=2022-11-28 |archive-date=2021-05-05 |archive-url=https://web.archive.org/web/20210505013431/https://babel.hathitrust.org/cgi/pt?id=uiug.30112025711521&view=1up&seq=829 |dead-url=no }}</ref>1908年，伊斯特拉外科医生{{le|安东尼奥·格罗西奇|Antonio Grossich}}在外科手术中使用[[碘酊]]来快速消毒人体皮肤。<ref>{{cite journal |vauthors=Grossich A |title=Eine neue Sterilisierungsmethode der Haut bei Operationen |journal=Zentralblatt für Chirurgie |date=31 October 1908 |volume=35 |issue=44 |pages=1289–1292 |url=https://babel.hathitrust.org/cgi/pt?id=uc1.b4150494&view=1up&seq=1305 |trans-title=A new method of sterilization of the skin for operations |language=de|access-date=2022-11-28 |archive-date=2021-05-05 |archive-url=https://web.archive.org/web/20210505130854/https://babel.hathitrust.org/cgi/pt?id=uc1.b4150494 |dead-url=no }}</ref>

在早期[[元素周期表]]中，碘的[[元素符号]]是源自[[德文]]''Jod''的'''J'''。<ref>{{cite web |title=Mendeleev's First Periodic Table |url=https://web.lemoyne.edu/giunta/EA/MENDELEEVann.HTML |website=web.lemoyne.edu |access-date=2022-11-28 |archive-date=2021-05-10 |archive-url=https://web.archive.org/web/20210510014806/https://web.lemoyne.edu/GIUNTA/EA/MENDELEEVann.HTML |dead-url=no }}</ref>这种元素的中文名称取自英文名稱的最後一個音節（dine→典），加上代表固體非金屬元素的「石」字部首，命名為「碘」。<ref>{{cite web|author=劉廣定|url=http://resource.blsh.tp.edu.tw/science-i/content/1985/00100190/0008.htm|title=中文化學名詞的演變（上）|publisher=《科學月刊》|date=1985年10月|access-date=2022-11-28|archive-date=2020-05-12|archive-url=https://web.archive.org/web/20200512190327/http://resource.blsh.tp.edu.tw/science-i/content/1985/00100190/0008.htm|dead-url=unfit}}</ref>

==性质==
{{main|碘化物|双原子碘}}
[[File:IodoAtomico.JPG|left|thumb|186x186px|碘可以升华成为紫色的气体]]
碘是第四个[[卤素]]，也是在有稳定同位素的卤素中最重的。（接下来的卤素[[砹]]和[[鿬]]因为它们极强的放射性并没有完整研究，但因为[[相对论量子化学|相对论效应]]而呈现出各种不寻常的性质。）碘的电子排布为[Kr]4d<sup>10</sup>5s<sup>2</sup>5p<sup>5</sup>，最外层有七个[[价电子]]。和其它卤素一样，碘只差一个电子就能达到[[八隅体]]结构，因此是会和许多元素反应来达到稳定八隅体结构的氧化剂。根据[[元素周期律]]，碘是稳定卤素中氧化性最弱的，其[[电负性]]也是最低的，仅2.66。（作为比较，氟、氯和溴的电负性分别为3.98、3.16和2.96，而砹则继续这个趋势，电负性来到了更低的2.2。）碘单质以[[双原子分子]] I<sub>2</sub>存在，这两个碘原子共用一对电子来达到稳定的八隅体结构。在高温下，这些双原子分子会可逆分解成一对碘原子。碘离子 I<sup>−</sup>是稳定卤素中还原性最强的，容易氧化成I<sub>2</sub>。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}（砹则继续这个趋势，其阴离子At<sup>−</sup>不稳定，很容易氧化成At<sup>0</sup>或At<sup>+</sup>。）<ref>{{cite book | series = Gmelin Handbook of Inorganic and Organometallic Chemistry | title = 'At, Astatine', System No. 8a | edition=8th | year = 1985 | publisher = Springer-Verlag | isbn = 978-3-540-93516-2 | vauthors = Kugler HK, Keller C | volume = 8 }}</ref>

碘微溶于水，在20℃时，碘在水中的溶解度为0.03g/100g。<ref name="CRC Handbook of Chemistry and Physics 97th Edition">{{Cite book |  date = 2016-06-24  |  title = CRC Handbook of Chemistry and Physics 97th Edition | pages = 4-66 | language = 英语 | ISBN = 1-4987-5428-7}}</ref>在水中加入[[碘化钾]]会因为产生[[三碘阴离子]]和其它[[多碘离子]]而增加碘的溶解度。{{sfn|Greenwood|Earnshaw|1997|pp=804–9}}像是[[己烷]]和[[四氯化碳]]的非极性溶剂则可以溶解更多的碘。<ref>{{cite book| title = Merck Index of Chemicals and Drugs| url = https://archive.org/details/merckindexencycl0009unse| edition = 9th| date = 1976| isbn=978-0-911910-26-1| editor = Windholz, Martha| editor2 = Budavari, Susan| editor3 = Stroumtsos, Lorraine Y.| editor4 = Fertig, Margaret Noether| publisher = J A Majors Company}}</ref>碘的极性溶液（例如水溶液）是棕色的，显示溶剂充当了[[路易斯碱]]，生成[[电荷转移配合物]]；而非极性溶液则呈现紫色，也就是碘原本的颜色。{{sfn|Greenwood|Earnshaw|1997|pp=804–9}}<ref name="King">{{cite book | vauthors = King RB |date=1995 |title=Inorganic Chemistry of Main Group Elements |publisher=Wiley-VCH |pages=173–98|isbn=978-0-471-18602-1}}</ref>

[[File:Iodine-triphenylphosphine charge-transfer complex in dichloromethane.jpg|thumb|upright=1.8|right|溶于[[二氯甲烷|CH<sub>2</sub>Cl<sub>2</sub>]]的电荷转移配合物I<sub>2</sub>•[[三苯基膦|PPh<sub>3</sub>]]。从左到右：<br />(1) I<sub>2</sub>溶于二氯甲烷并不产生电荷转移配合物。<br />(2) 在加入过量PPh<sub>3</sub>几秒后逐渐产生电荷转移配合物。<br />(3) 在加入过量PPh<sub>3</sub>一分钟后产生电荷转移配合物[Ph<sub>3</sub>PI]<sup>+</sup>I<sup>−</sup>。<br />(4) 在加入过量I<sub>2</sub>后产生的电荷转移配合物是[Ph<sub>3</sub>PI]<sup>+</sup>[I<sub>3</sub>]<sup>−</sup>。<ref name="InorgChem">{{Housecroft3rd|page=541}}</ref>]]

碘的熔点和沸点是稳定卤素当中最高的，符合元素周期律。碘是卤素中挥发性最低的，但固态碘仍会产生紫色蒸汽。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}由于这个性质，碘可用于示范从[[固体]]直接变为[[气体]]的[[升华]]过程，但这也使人误解碘在[[标准大气压]]下没有[[液态]]。<ref>{{cite journal |title=The concept of sublimation – iodine as an example |journal=Educación Química |date=1 March 2012 |volume=23 |pages=171–175 |url=https://www.sciencedirect.com/science/article/pii/S0187893X17301490 |doi=10.1016/S0187-893X(17)30149-0 |language=en |issn=0187-893X |doi-access=free |vauthors=Stojanovska M, Petruševski VM, Šoptrajanov B |access-date=2022-11-29 |archive-date=2022-11-08 |archive-url=https://web.archive.org/web/20221108140442/https://www.sciencedirect.com/science/article/pii/S0187893X17301490 |dead-url=no }}</ref>由于碘在稳定卤素当中有最大的[[原子半径]]，它的[[电离能]]、[[电子亲和能]]、[[电负性]]和反应性也都是稳定卤素中最低。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}

[[File:Iodine-unit-cell-3D-balls-B.png|thumb|upright=0.7|right|碘的晶体结构]]
I<sub>2</sub>中的键是所有卤素中最弱的。在575&nbsp;°C下的气态碘就有1%离解成碘原子，而其它卤素要达到这种离解程度需要750&nbsp;°C以上的温度。大多数含碘的键比较轻卤素的键弱。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}气态碘由I<sub>2</sub>分子组成，其I–I键长为266.6&nbsp;pm，是最长的单键之一。在碘[[正交晶系]]的晶体中，其I–I键长会变长，达到271.5&nbsp;pm。<ref>{{cite book| title = Advanced Structural Inorganic Chemistry| url = https://archive.org/details/advancedstructur0000liwa| url-access = limited| vauthors = Li WK, Zhou GD, Mak TC | publisher = Oxford University Press| date = 2008| isbn = 978-0-19-921694-9| page = [https://archive.org/details/advancedstructur0000liwa/page/674 674]}}</ref>这使得在碘分子中有显著的电子相互作用，而这些相互作用使碘是[[半导体]]，且有闪亮的外观。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}碘是二维半导体，[[能隙]]为1.3&nbsp;eV（125&nbsp;kJ/mol）。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}

=== 同位素 ===
{{main|碘的同位素}}
碘有37種[[同位素]]，其中只有碘-127穩定、存在于自然界。其它同位素都具有放射性，且半衰期都短到不能成为{{le|原生核素|primordial nuclide}}。因此，碘屬於[[單一同位素元素]]。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}

最稳定的放射性碘同位素是[[碘-129]]，半衰期长达1614万年，会[[β衰变]]成稳定的[[氙]]-129。<ref name="NUBASE">{{NUBASE2020}}</ref>在太阳系形成之前就存在和碘-127一同产生的碘-129，但到了今天已全部衰变，成为{{le|绝种同位素|extinct radionuclide}}。碘-129可以为早期太阳系或非常古老的地下水测年，其存在可以通过样本过量的[[衰变产物]]氙-129确定。<ref>{{cite journal | vauthors = Watson JT, Roe DK, Selenkow HA | title = Iodine-129 as a "nonradioactive" tracer | journal = Radiation Research | volume = 26 | issue = 1 | pages = 159–163 | date = September 1965 | pmid = 4157487 | doi = 10.2307/3571805 | bibcode = 1965RadR...26..159W | jstor = 3571805 }}</ref><ref>{{cite web |url=https://e-reports-ext.llnl.gov/pdf/234761.pdf | vauthors = Santschi PH, Moran JE, Oktay S, Hoehn E, Sharma P |date=1998 |title=129Iodine: A new tracer for surface water/groundwater interaction |publisher=Lawrence Livermore National Laboratory preprint UCRL-JC-132516. |location=Livermore, US|archive-url=https://web.archive.org/web/20161221192732/https://e-reports-ext.llnl.gov/pdf/234761.pdf|archive-date=21 December 2016|url-status=dead}}</ref><ref>{{cite journal | vauthors = Snyder G, Fabryka-Martin J | year = 2007 | title = I-129 and Cl-36 in dilute hydrocarbon waters: Marine-cosmogenic, in situ, and anthropogenic sources | journal = Applied Geochemistry | volume = 22 | issue = 3| pages = 692–714 | doi = 10.1016/j.apgeochem.2006.12.011 | bibcode = 2007ApGC...22..692S }}</ref><ref>{{cite book| vauthors = Clayton DD |year=1983|title=Principles of Stellar Evolution and Nucleosynthesis| url=https://archive.org/details/principlesofstel0000clay|url-access=registration|page=[https://archive.org/details/principlesofstel0000clay/page/75 75]|edition=2nd|publisher=University of Chicago Press|isbn=978-0-226-10953-4}}</ref><ref>{{cite web|vauthors=Bolt BA, Packard RE, Price PB|year=2007|url=http://content.cdlib.org/xtf/view?docId=hb1r29n709&doc.view=content&chunk.id=div00061&toc.depth=1&brand=oac&anchor.id=0|title=John H. Reynolds, Physics: Berkeley|publisher=The University of California, Berkeley|access-date=2007-10-01|archive-date=2012-05-24|archive-url=https://archive.today/20120524185517/http://content.cdlib.org/xtf/view?docId=hb1r29n709&doc.view=content&chunk.id=div00061&toc.depth=1&brand=oac&anchor.id=0|dead-url=no}}</ref>自然界中仍有痕量的碘-129，它们是由大气中氙的[[宇宙射线散裂]]而成的，占了天然碘的10<sup>−14</sup>至10<sup>−10</sup>。碘-129也可以通过核试验产生。不过，在核试验最多的1960和1970年代，碘-129仍只占了天然碘的10<sup>−7</sup>。<ref name="SCOPE50">
[http://www.scopenvironment.org/downloadpubs/scope50 SCOPE 50 - Radioecology after Chernobyl] {{webarchive|url=https://web.archive.org/web/20140513065145/http://www.scopenvironment.org/downloadpubs/scope50/ |date=13 May 2014 }}, the Scientific Committee on Problems of the Environment (SCOPE), 1993. See table 1.9 in Section 1.4.5.2.</ref>碘-127和碘-129的激发态可用于[[穆斯堡尔谱学]]。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}

其它碘同位素的半衰期则更短，都不超过几天，<ref name="NUBASE" />其中一些可用于医疗。[[碘-123]]的半衰期为13小时，会[[电子捕获]]成[[碲-123]]并放出[[γ射线]]，可用于{{le|单光子发射计算机断层扫描|single photon emission computed tomography}}（SPECT）和[[CT扫描]]。<ref>{{cite journal | vauthors = Hupf HB, Eldridge JS, Beaver JE | title = Production of iodine-123 for medical applications | journal = The International Journal of Applied Radiation and Isotopes | volume = 19 | issue = 4 | pages = 345–351 | date = April 1968 | pmid = 5650883 | doi = 10.1016/0020-708X(68)90178-6 }}</ref>[[碘-125]]是半衰期第二长的放射性碘同位素，半衰期为59天，会电子捕获成[[碲-125]]，并放出低能量γ射线。它可用于{{le|化验|biological assay}}、[[核医学]]和[[近距离治疗]]，可以治疗[[前列腺癌]]、{{le|葡萄膜黑色素瘤|uveal melanoma}}和[[脑瘤]]。<ref>Harper, P.V.; Siemens, W.D.; Lathrop, K.A.; Brizel, H.E.; Harrison, R.W. ''Iodine-125.'' Proc. Japan Conf. Radioisotopes; Vol: 4th Jan 01, 1961</ref>半衰期8天的[[碘-131]]则会β衰变成稳定的[[氙-131]]的激发态，后者会释放γ射线来回到基态。碘-131是常见的[[裂变产物]]，因此会在[[放射性落下灰]]中大量存在。人体可能会通过受污染的食物吸收它，积聚在甲状腺中。它的衰变可能会损害甲状腺，造成[[甲状腺癌]]和[[甲状腺炎]]。<ref name="Rivkees">{{cite journal | vauthors = Rivkees SA, Sklar C, Freemark M | title = Clinical review 99: The management of Graves' disease in children, with special emphasis on radioiodine treatment | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 83 | issue = 11 | pages = 3767–3776 | date = November 1998 | pmid = 9814445 | doi = 10.1210/jcem.83.11.5239 }}</ref>

防止碘-131影响人体的常用方法是每天服用含稳定的碘-127的[[碘化钾]]片来使甲状腺饱和。<ref>{{cite journal | vauthors = Zanzonico PB, Becker DV | title = Effects of time of administration and dietary iodine levels on potassium iodide (KI) blockade of thyroid irradiation by 131I from radioactive fallout | journal = Health Physics | volume = 78 | issue = 6 | pages = 660–667 | date = June 2000 | pmid = 10832925 | doi = 10.1097/00004032-200006000-00008 | s2cid = 30989865 }}</ref>不过当需要破坏组织时，碘-131也可用于[[放射疗法]]。<ref>{{cite news|title=Medical isotopes the likely cause of radiation in Ottawa waste|url=http://www.cbc.ca/news/canada/medical-isotopes-the-likely-cause-of-radiation-in-ottawa-waste-1.852645|date=4 February 2009|publisher=[[CBC News]]|access-date=30 September 2015|archive-date=2021-11-19|archive-url=https://web.archive.org/web/20211119213013/https://www.cbc.ca/news/canada/medical-isotopes-the-likely-cause-of-radiation-in-ottawa-waste-1.852645|dead-url=no}}</ref>碘-131可用作[[放射性示踪剂]]。<ref>{{cite book| vauthors = Moser H, Rauert W |title=Isotopes in the water cycle : past, present and future of a developing science|year=2007|publisher=Springer|location=Dordrecht|isbn=978-1-4020-6671-9 | veditors = Aggarwal PK, Gat JR, Froehlich KF |access-date=6 May 2012|page=11|chapter=Isotopic Tracers for Obtaining Hydrologic Parameters|chapter-url=https://books.google.com/books?id=XKk6V_IeJbIC&pg=PA11}}</ref><ref>{{cite book| vauthors = Rao SM |title=Practical isotope hydrology|year=2006|publisher=New India Publishing Agency|location=New Delhi|isbn=978-81-89422-33-2|chapter-url=https://books.google.com/books?id=E7TVDVVji0EC&q=isotope%20hydrology%20iodine&pg=PA11|access-date=6 May 2012|pages=12–13|chapter=Radioisotopes of hydrological interest}}</ref><ref>{{cite web|title=Investigating leaks in Dams & Reservoirs|url=http://www.iaea.org/technicalcooperation/documents/sheet20dr.pdf|work=IAEA.org|access-date=6 May 2012|archive-url=https://web.archive.org/web/20130730053205/http://www.iaea.org/technicalcooperation/documents/sheet20dr.pdf|archive-date=30 July 2013|url-status=dead}}</ref><ref>{{cite book| vauthors = Araguás LA, Bedmar AP |title=Detection and prevention of leaks from dams|year=2002|publisher=Taylor & Francis|isbn=978-90-5809-355-4|chapter-url=https://books.google.com/books?id=FXB-HMzfBnkC&pg=PA179 |access-date=6 May 2012|pages=179–181|chapter=Artificial radioactive tracers}}</ref>

== 化学性质和化合物 ==
{| class="wikitable" style="float:right; margin-top:0; margin-left:1em; text-align:center; font-size:10pt; line-height:11pt; width:25%;"
|+ style="margin-bottom: 5px;" | 卤素键键能（kJ/mol）{{sfn|Greenwood|Earnshaw|1997|pp=804–9}}
|-
! X
! XX
! HX
! BX<sub>3</sub>
! AlX<sub>3</sub>
! CX<sub>4</sub>
|-
! F
| 159
| 574
| 645
| 582
| 456
|-
! Cl
|243
|428
|444
|427
|327
|-
! Br
|193
|363
|368
|360
|272
|-
! I
|151
|294
|272
|285
|239
|}
碘很活泼，但比其它卤素不活泼。举个例子，氯气可以把[[一氧化碳]]、[[一氧化氮]]和[[二氧化硫]]分别氯化成[[光气]]、[[亚硝酰氯]]和[[硫酰氯]]，但碘不能。此外，金属的碘化物可以达到的价态往往比对应的氯化物和溴化物低。举个例子，[[铼]]的最高价氯化物是[[六氯化铼]]，而最高价溴化物是五溴化铼，但铼的最高价碘化物只是四碘化铼。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}出于同样的原因，碘在卤素中最低的电离能代表它最容易给氧化，因此阳离子化学也较多。它的高氧化态也比溴和氯稳定，其中一个例子就是[[七氟化碘]]。{{sfn|Greenwood|Earnshaw|1997|pp=804–9}}

===电荷转移配合物 ===
碘分子 I<sub>2</sub>可溶于CCl<sub>4</sub>和碳氢化合物中，产生亮紫色的溶液。这些溶液的吸收带高峰在520 &ndash; 540&nbsp;nm的区间，是{{pi}}<sup>*</sup>至''σ''<sup>*</sup>跃迁产生的。I<sub>2</sub>和路易斯碱反应会使这个吸收带高峰蓝移到230 &ndash; 330&nbsp;nm，这是因反应产生的加合物（也就是电荷转移配合物）导致的。{{sfn|Greenwood|Earnshaw|1997|pp=806–7}}

===碘化氢===
{{main|碘化氢|氢碘酸}}
碘最简单的化合物是[[碘化氢]] HI。它是无色气体，会给氧气氧化成水和碘。和其它卤化氢不同，虽然碘化氢在实验室里可用于[[碘化]]反应，但它没有大规模工业用途。碘化氢在商业上是由碘和[[硫化氢]]或[[联氨]]反应而成的：{{sfn|Greenwood|Earnshaw|1997|pp=809–12}}<ref name="glinka">{{Cite book| title = General Chemistry| volume = 2|last = Glinka |first=N. L.| publisher = Mir Publishing|date = 1981}}</ref>
:8 I<sub>2</sub> + 8 H<sub>2</sub>S → 16 HI + S<sub>8</sub>
:2 I<sub>2</sub> + N<sub>2</sub>H<sub>4</sub> {{overset|H<sub>2</sub>O|⟶}} 4 HI + N<sub>2</sub>
在室温下，碘化氢是无色气体，熔点−51.0&nbsp;°C，沸点−35.1&nbsp;°C。它是[[吸热]]化合物，其分解反应放热，但除非有[[催化剂]]，否则反应非常缓慢。这也使得氢气和碘在室温下不会完全反应。碘化氢中H–I键的[[键解离能]]是所有卤化氢中最小的，只有295&nbsp;kJ/mol。{{sfn|Greenwood|Earnshaw|1997|pp=812–9}}

碘化氢的水溶液[[氢碘酸]]是一种强酸。碘化氢极易溶于水，一升水就可以溶解425升的碘化氢，而其饱和溶液中水分子和碘化氢分子的比例达到了4:1。<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.</ref>市面上的浓氢碘酸的含48–57% HI。浓度为56.7%的氢碘酸是[[共沸物]]，沸点为126.7&nbsp;°C，因此到达这个浓度的氢碘酸无法通过蒸馏继续浓缩。{{sfn|Greenwood|Earnshaw|1997|pp=812–9}}

和[[氟化氢]]不同，无水碘化氢因为沸点低且液态范围小，因此是极差的溶剂。碘化氢的[[相对介电常数]]低，且不会明显离解成H<sub>2</sub>I<sup>+</sup>和{{chem|HI|2|-}}离子。由于氢和碘之间的氢键很弱，{{chem|HI|2|-}}比[[氟化氢根|{{chem|HF|2|-}}]]不稳定许多，但它的[[铯|Cs<sup>+</sup>]]和[[季铵阳离子|{{chem|NR|4|+}}]]（R = [[甲基|Me]]、[[乙基|Et]]、[[正丁基|Bu<sup>''n''</sup>]]）盐仍可给分离。无水碘化氢只能溶解像[[亚硝酰氯]]和[[苯酚]]这样的小分子，或是像季铵盐这样[[晶格能]]很低的离子化合物。{{sfn|Greenwood|Earnshaw|1997|pp=812–9}}

===其它碘化物===
{{main|碘化物}}
大部分元素都可以形成[[碘化物]]。不过，由于碘离子较大且碘的氧化性较弱，碘化物很难达到高氧化态。在已知的碘化物中，金属的最高氧化态是+5，存在于[[铌]]、[[钽]]和[[镤]]的五碘化物中。不会水解的碘化物可以由对应元素或其氧化物、氢氧化物或碳酸盐和氢碘酸反应而成，然后在碘化氢气氛下脱水而成。其它制备碘化物的方法包括元素和碘或碘化氢在高温下的反应，或是在高温下用碘单质、挥发性的金属碘化物、[[四碘化碳]]或有机碘化合物碘化金属氧化物或其它卤化物而成。举个例子，[[二氧化钼]]和[[三碘化铝]]在230&nbsp;°C下反应，生成[[二碘化钼]]。一个涉及卤素交换的反应见下，是[[五氯化钽]]和过量的三碘化铝在400&nbsp;°C下生成[[五碘化钽]]的反应：{{sfn|Greenwood|Earnshaw|1997|pp=821–4}}

: <chem>3TaCl5 + \underset{(excess)}{5AlI3} -> 3TaI5 + 5AlCl3</chem>

低价碘化物则可以由热分解或歧化产生，也可以通过高价碘化物给氢气或金属还原而成：{{sfn|Greenwood|Earnshaw|1997|pp=821–4}}

: <chem>TaI5{} + Ta ->[\text{thermal gradient}] [\ce{630^\circ C\ ->\ 575^\circ C}] Ta6I14</chem>

金属的低氧化态（+1，+2）碘化物偏向于离子化合物，而非金属和氧化态超过+3的金属碘化物则偏向于共价化合物。+3氧化态的金属碘化物可能是离子化合物也可能是共价化合物（例如[[碘化钪]]是离子化合物，而[[三碘化铝]]是共价化合物）。离子碘化物MI<sub>''n''</sub>在对应的卤化物MX<sub>''n''</sub>中有最低的熔沸点，而共价碘化物在对应的卤化物中有最高的熔沸点。类似的，离子碘化物（例如[[碘化钾]]和[[碘化钙]]）在水中的溶解度是对应的卤化物中最高的，而共价碘化物（例如[[碘化银]]）在水中的溶解度则是对应的卤化物中最低的。[[碘化银]]极难溶于水的性质可用于检测碘的存在。{{sfn|Greenwood|Earnshaw|1997|pp=821–4}}

===卤化物===
碘会形成三种一卤化物、三氟化物、三氯化物、五氟化物以及其它卤素都没有的七氟化物。卤化碘离子也是已知的，如酒红或橙色的{{chem|ICl|2|+}}以及深棕或紫黑色的I<sub>2</sub>Cl<sup>+</sup>。除此之外，碘也可以和[[拟卤素]]形成化合物，例如[[碘化氰]]（ICN）、硫氰酸碘（ISCN）和[[叠氮化碘]]（IN<sub>3</sub>）。{{sfn|Greenwood|Earnshaw|1997|pp=824–8}}

[[File:Iodine monochloride1.jpg|thumb|right|一氯化碘]]
[[一氟化碘]]（IF）在室温下不稳定，会迅速歧化成碘和[[五氟化碘]]，因此不能提纯。它可以由在[[三氯氟甲烷]]里，碘和−45&nbsp;°C的氟气、−78&nbsp;°C的[[三氟化碘]]或是0&nbsp;°C的[[氟化银]]反应而成。{{sfn|Greenwood|Earnshaw|1997|pp=824–8}}[[一氯化碘]]（ICl）和[[一溴化碘]]（IBr）较稳定。一氯化碘是挥发性的红棕色化合物，由[[约瑟夫·路易·盖-吕萨克]]和[[汉弗里·戴维]]在1813–1814年独立发现。一氯化碘和溴单质很相似，这使得[[尤斯图斯·冯·李比希]]误把他发现的溴当成了一氯化碘。<ref>{{cite journal | last=Weeks | first=Mary Elvira | title=The discovery of the elements. XVII. The halogen family | journal=Journal of Chemical Education | publisher=American Chemical Society (ACS) | volume=9 | issue=11 | year=1932 | issn=0021-9584 | doi=10.1021/ed009p1915 | page=1915}}</ref>一氯化碘和一溴化碘可由碘直接和对应卤素反应而成，然后通过{{le|分级结晶|fractional crystallization (chemistry)}}提纯。它们都很活泼，甚至可以腐蚀[[铂]]和[[金]]，但不能腐蚀[[硼]]、[[碳]]、[[镉]]、[[铅]]、[[锆]]、[[铌]]、[[钼]]和[[钨]]。它们和有机化合物的反应取决于条件。一氯化碘蒸汽与[[苯酚]]和[[水杨酸]]的反应是氯化反应。这是因为一氯化碘[[均裂]]时会产生氯和碘，而氯更活泼。不过，在一氯化碘的四氯化碳溶液和苯酚的反应中，碘化反应会成为主反应。这是因为在溶液中，I–Cl键倾向于[[异裂]]，产生的I<sup>+</sup>离子会作为亲电试剂和苯酚反应。由于一溴化碘倾向于均裂成元素，而溴又比碘活泼，因此一溴化碘的四氯化碳溶液仍会溴化苯酚。{{sfn|Greenwood|Earnshaw|1997|pp=824–8}}液态一氯化碘和一溴化碘会离解成{{chem|I|2|X|+}}和{{chem|IX|2|-}}（X = Cl、Br）离子，显著增加它们的导电能力。{{sfn|Greenwood|Earnshaw|1997|pp=824–8}}

[[三氟化碘]]（IF<sub>3</sub>）是不稳定的黄色固体，−28&nbsp;°C时就会分解，因此鲜为人知。由于氟气会直接把碘氟化成五氟化碘，因此制备三氟化碘需要用[[二氟化氙]]在[[三氯氟甲烷]]下氟化碘。<ref>{{cite book | last=Klapötke | first=Thomas M. | last2=Tornieporth-Oetting | first2=Inis C. | title=Nichtmetallchemie | publication-place=Weinheim | date=1994 | isbn=978-3-527-29052-9 | oclc=844785618 | language=de}}</ref>[[三氯化碘]]是亮黄色固体，可以由碘和液氯在−80&nbsp;°C下反应而成，在固态下以平面形二聚体I<sub>2</sub>Cl<sub>6</sub>存在。它是强氯化剂。液态三氯化碘可以导电，表明它会离解成{{chem|ICl|2|+}}和{{chem|ICl|4|-}}离子。{{sfn|Greenwood|Earnshaw|1997|pp=828–831}}

[[五氟化碘]]（IF<sub>5</sub>）是无色、有挥发性的液体。它是热力学上最稳定的氟化碘，可以由碘和氟气在室温下反应而成。它是氟化剂，但可以储存在玻璃容器中。液态五氟化碘离解的{{chem|IF|4|+}}和{{chem|IF|6|-}}使它可以导电。有着[[五角双锥形分子构型]]的[[七氟化碘]]（IF<sub>7</sub>）可以通过五氟化碘进一步和氟气反应产生。<ref>{{cite journal | title = Das Jod-7-fluorid [The iodine-7-fluoride]| author1 = Ruff, O. | author2 = Keim, R. | journal = Zeitschrift für anorganische und allgemeine Chemie | language = de| year = 1930 | volume = 193 | issue = 1 | pages = 176–186 | doi = 10.1002/zaac.19301930117 }}</ref>它是极强的氟化剂，在互卤化物中仅次于[[三氟化氯]]、[[五氟化氯]]和[[五氟化溴]]。即使在低温下，七氟化碘仍会和几乎所有的元素反应，氟化[[派热克斯玻璃]]并产生[[五氟氧化碘]]（IOF<sub>5</sub>），还可以使一氧化碳燃烧。{{sfn|Greenwood|Earnshaw|1997|pp=832–835}}

===含氧化合物===
[[File:Iodine-pentoxide-3D-balls.png|thumb|right|upright=0.7|五氧化二碘的结构]]
由于碘和氧较大的电负性差距增强了I–O键，因此[[碘的氧化物]]也是卤素的氧化物中最稳定、发现时间最早的。<ref name="King" />白色的[[五氧化二碘]]（I<sub>2</sub>O<sub>5</sub>）在1813年由盖-吕萨克和戴维发现，可由[[碘酸]]（HIO<sub>3</sub>）脱水而成。它会迅速把一氧化碳氧化成[[二氧化碳]]，因此可用于测量一氧化碳浓度。除此之外，五氧化二碘也会氧化氮氧化物、[[乙烯]]和[[硫化氢]]。它和[[三氧化硫]]和[[过二硫酰氟]]（S<sub>2</sub>O<sub>6</sub>F<sub>2</sub>）反应，生成含有碘酰阳离子 [IO<sub>2</sub>]<sup>+</sup>的盐。这种盐可以给浓[[硫酸]]还原成含有[IO]<sup>+</sup>离子的亚碘酰盐。五氧化二碘可以给氟气、三氟化溴、[[四氟化硫]]和[[氯酰氟]]氟化成五氟化碘，而五氟化碘也可以和五氧化二碘反应，产生[[三氟氧化碘]] IOF<sub>3</sub>。碘也有其它较不稳定的氧化物，如[[九氧化四碘|I<sub>4</sub>O<sub>9</sub>]]和[[四氧化二碘|I<sub>2</sub>O<sub>4</sub>]]。它们的结构仍未得以确认，但合理猜测分别是I<sup>III</sup>(I<sup>V</sup>O<sub>3</sub>)<sub>3</sub>和[IO]<sup>+</sup>[IO<sub>3</sub>]<sup>−</sup>。{{sfn|Greenwood|Earnshaw|1997|pp=851–3}}

{| class="wikitable" style="float:right; margin-top:0; margin-left:1em; text-align:center; font-size:10pt; line-height:11pt; width:25%;"
|+ 含碘物种的标准电极电势{{sfn|Greenwood|Earnshaw|1997|pp=853–9}}
! {{nowrap|E°}}!!{{nowrap|''a''(H<sup>+</sup>) {{=}} 1}}<br />（酸性）!!{{nowrap|E°}}!!{{nowrap|''a''(OH<sup>−</sup>) {{=}} 1}}<br />（碱性）
|-
|I<sub>2</sub>/I<sup>−</sup>||+0.535|||I<sub>2</sub>/I<sup>−</sup>||+0.535
|-
|HOI/I<sup>−</sup>||+0.987||IO<sup>−</sup>/I<sup>−</sup>||+0.48
|-
|&nbsp;||&nbsp;||{{chem|IO|3|-}}/I<sup>−</sup>||+0.26
|-
|HOI/I<sub>2</sub>||+1.439||IO<sup>−</sup>/I<sub>2</sub>||+0.42
|-
|{{chem|IO|3|-}}/I<sub>2</sub>||+1.195||&nbsp;||&nbsp;
|-
|{{chem|IO|3|-}}/HOI||+1.134||{{chem|IO|3|-}}/IO<sup>−</sup>||+0.15
|-
|{{chem|IO|4|-}}/{{chem|IO|3|-}}||+1.653||&nbsp;||&nbsp;
|-
|H<sub>5</sub>IO<sub>6</sub>/{{chem|IO|3|-}}||+1.601||{{chem|H|3|IO|6|2-}}/{{chem|IO|3|-}}||+0.65
|}
除了氧化物之外，碘也可以形成含氧酸[[次碘酸]]（HIO）、[[亚碘酸]]（HIO<sub>2</sub>）、[[碘酸]]（HIO<sub>3</sub>）和[[高碘酸]]（HIO<sub>4</sub>或H<sub>5</sub>IO<sub>6</sub>）。碘溶于水时会产生以下反应：{{sfn|Greenwood|Earnshaw|1997|pp=853–9}}
:{|
|-
| I<sub>2</sub> + H<sub>2</sub>O || {{eqm}} HIO + H<sup>+</sup> + I<sup>−</sup> || ''K''<sub>ac</sub> = 2.0 × 10<sup>−13</sup> mol<sup>2</sup> l<sup>−2</sup>
|-
| I<sub>2</sub> + 2 OH<sup>−</sup> || {{eqm}} IO<sup>−</sup> + H<sub>2</sub>O + I<sup>−</sup> || ''K''<sub>alk</sub> = 30&nbsp;mol<sup>2</sup> l<sup>−2</sup>
|}

次碘酸很不稳定。次碘酸盐会歧化成碘化物和碘酸盐：{{sfn|Greenwood|Earnshaw|1997|pp=853–9}}
:{|
|-
| 3 IO<sup>−</sup> {{eqm}} 2 I<sup>−</sup> + {{chem|IO|3|-}} || ''K'' = 10<sup>20</sup>
|}

亚碘酸和亚碘酸盐比次碘酸和次碘酸盐更不稳定，只是碘化物氧化成碘酸盐的中间体。{{sfn|Greenwood|Earnshaw|1997|pp=853–9}}碘酸盐是最重要的碘含氧酸盐，可由[[碱金属]]碘化物在600&nbsp;°C和高压下与氧气反应而成，或是用[[氯酸盐]]氧化碘而成。不像会缓慢歧化成氯化物和高氯酸盐的氯酸盐，碘酸盐在酸性和碱性条件下都不会歧化。碘酸可通过对碘的水溶液[[电解]]或加入发烟[[硝酸]]而成。碘酸盐的氧化性比氯酸盐和[[溴酸盐]]弱，但反应速度比它们快。{{sfn|Greenwood|Earnshaw|1997|pp=863–4}}

高碘酸盐有很多种，除了四面体形的偏高碘酸根 {{chem|IO|4|-}}以外，还有四方锥形的{{chem|IO|5|3-}}、八面体形的正高碘酸根 {{chem|IO|6|5-}}、[IO<sub>3</sub>(OH)<sub>3</sub>]<sup>2−</sup>、[I<sub>2</sub>O<sub>8</sub>(OH<sub>2</sub>)]<sup>4−</sup>和{{chem|I|2|O|9|4-}}。它们可由在碱性环境下用电化学法（需要[[二氧化铅]]阳极）或氯气氧化[[碘酸钠]]而成：{{sfn|Greenwood|Earnshaw|1997|pp=872–5}}
:{{chem|IO|3|-}} + 6 OH<sup>−</sup> → {{chem|IO|6|5-}} + 3 H<sub>2</sub>O + 2 e<sup>−</sup>
:{{chem|IO|3|-}} + 6 OH<sup>−</sup> + Cl<sub>2</sub> → {{chem|IO|6|5-}} + 2 Cl<sup>−</sup> + 3 H<sub>2</sub>O

高碘酸盐在热力学上和动力学上都是强氧化剂，会迅速把Mn<sup>2+</sup>氧化成[[高锰酸盐|{{chem|MnO|4|-}}]]，也会使[[二醇]]、α-[[二酮]]、α-{{le|羟酮|ketol}}、α-[[氨基醇]]、α-[[二胺]]裂解。{{sfn|Greenwood|Earnshaw|1997|pp=872–5}}[[正高碘酸]] H<sub>5</sub>IO<sub>6</sub>在100&nbsp;°C的真空下脱水会形成[[偏高碘酸]] HIO<sub>4</sub>。继续脱水并不会得到七氧化二碘（I<sub>2</sub>O<sub>7</sub>），而是五氧化二碘和氧气。正高碘酸和[[硫酸]]反应，可以得到{{chem|I(OH)|6|+}}阳离子（和[[原碲酸|Te(OH)<sub>6</sub>]]及{{chem|Sb(OH)|6|-}}是[[等电子体]]）的硫酸盐和硫酸氢盐。<ref name="King" />

===多碘化合物===
碘溶于如发烟硫酸的强酸时会生成含有亮蓝色、[[顺磁性]]的{{chem|I|2|+}}离子的溶液。
[[File:Diiodine cation.jpg | thumb | right | 发烟硫酸中的I₂⁺，溶液呈现蓝色]]
{{chem|I|2|+}}的盐可由由碘和[[五氟化锑]]反应而成：<ref name="King" />
:2 I<sub>2</sub> + 5 SbF<sub>5</sub> {{overunderset|{{big|⟶}}|SO<sub>2</sub>|20&nbsp;°C}} 2 I<sub>2</sub>Sb<sub>2</sub>F<sub>11</sub> + SbF<sub>3</sub>
它是深蓝色的化合物。类似的[[钽]]化合物I<sub>2</sub>Ta<sub>2</sub>F<sub>11</sub>也存在。I<sub>2</sub>中的I–I键长为267&nbsp;pm，而{{chem|I|2|+}}因为其[[反键轨道]]失去一个电子，增强了I–I键的强度，所以其键长也缩短成了256&nbsp;pm。

在−60&nbsp;°C的[[氟磺酸]]里，{{chem|I|2|+}}会可逆二聚成红色、长方形、有抗磁性的{{chem|I|4|2+}}。其它多碘阳离子也存在，如深棕黑色的{{chem|I|3|+}}和绿黑色的{{chem|I|5|+}}。<ref name="King" />{{sfn|Greenwood|Earnshaw|1997|pp=842–4}}
[[File:Triiodine cation.jpg | thumb | right | 通过硫酸介质下碘酸氧化碘单质得到的I₃⁺，溶液呈现棕色]]
[[File:Pentaiodine cation in sulfuric acid.jpg | thumb | right | 由硫酸介质下碘酸氧化碘单质得到的I₅⁺，溶液呈现绿黑色]]
在水溶液中最重要的[[多碘离子]]是线形的[[三碘离子]] {{chem|I|3|-}}，碘可溶于加有碘化钾的水就是因为这种离子。<ref name="King" />
:I<sub>2</sub> + I<sup>−</sup> {{eqm}} {{chem|I|3|-}}（20&nbsp;°C时 ''K''<sub>eq</sub> = ~700）
结晶含有碘和碘化物的溶液时也可以产生其它多碘阴离子，如{{chem|I|5|-}}、{{chem|I|9|-}}、{{chem|I|4|2-}}和{{chem|I|8|2-}}。它们和极化性弱的大阳离子（如[[铯|Cs<sup>+</sup>]]）形成的盐可分离。<ref name="King" />{{sfn|Greenwood|Earnshaw|1997|pp=835–9}}

===有机碘化合物===
{{main|有机碘化合物}}
[[File:IBXAcid.png|thumb|right|氧化剂[[2-碘酰基苯甲酸]]的结构]]
有机碘化合物一直是有机合成发展的基础，可用于[[霍夫曼消除反应]]<ref>{{cite journal | title = Beiträge zur Kenntniss der flüchtigen organischen Basen | journal = [[Annalen der Chemie und Pharmacie]] | volume = 78 | issue = 3 | year = 1851 | pages = 253–286 | vauthors = Hofmann AW | doi = 10.1002/jlac.18510780302 | url = https://zenodo.org/record/1427040 | access-date = 2022-12-02 | archive-date = 2022-12-01 | archive-url = https://web.archive.org/web/20221201072415/https://zenodo.org/record/1427040 | dead-url = no }}</ref>、[[威廉姆逊合成反应]]<ref>{{cite journal | title = Theory of Aetherification | journal = Philosophical Magazine | volume = 37 | issue = 251 | pages = 350–356 | year = 1850 | doi = 10.1080/14786445008646627 | vauthors = Williamson A | url = https://zenodo.org/record/1431121 | access-date = 2022-12-02 | archive-date = 2022-11-09 | archive-url = https://web.archive.org/web/20221109194527/https://zenodo.org/record/1431121 | dead-url = no }} ([http://web.lemoyne.edu/~giunta/williamson.html Link to excerpt.] {{Wayback|url=http://web.lemoyne.edu/~giunta/williamson.html |date=20190423075534 }})</ref>、[[武兹反应]]<ref>{{cite journal | title = Ueber eine neue Klasse organischer Radicale | vauthors = Wurtz A | journal = [[Annalen der Chemie und Pharmacie]] | volume = 96 | issue = 3 | pages = 364–375 | year = 1855 | url = https://zenodo.org/record/1427074 | doi = 10.1002/jlac.18550960310 | access-date = 2022-12-02 | archive-date = 2023-02-03 | archive-url = https://web.archive.org/web/20230203205851/https://zenodo.org/record/1427074 | dead-url = no }}</ref>和合成[[格氏试剂]]。<ref>{{cite journal | vauthors = Grignard V | title = Sur quelques nouvelles combinaisons organométaliques du magnésium et leur application à des synthèses d'alcools et d'hydrocabures | journal = Compt. Rend. | year = 1900 | volume = 130 | pages = 1322–25 | url = http://gallica.bnf.fr/ark:/12148/bpt6k3086n/f1322.table | author-link = Victor Grignard | access-date = 2022-12-02 | archive-date = 2019-08-08 | archive-url = https://web.archive.org/web/20190808225609/https://gallica.bnf.fr/ark:/12148/bpt6k3086n/f1322.table | dead-url = no }}</ref>

[[碳]]–碘键在[[有机化学]]中较为常见。[[碘代烃]]可由[[醇]]和[[三碘化磷]]反应而成，用于[[亲核取代反应]]和制备[[格氏试剂]]。C–I键因碳（2.55）和碘（2.66）的电负性差距不大，是所有碳–卤素键中最弱的。因此，碘离子是所有卤素离子中最好的[[离去基团]]，使得很多有机碘化合物放久了都会因为分解产生的碘而变黄。C–I键易于形成和消除的性质可用于[[有机合成]]。<ref>{{Ullmann | vauthors = Lyday PA | title = Iodine and Iodine Compounds | doi = 10.1002/14356007.a14_381}}</ref>碘的高原子量也使得有机碘化合物的密度比其它有机化合物高很多。<ref name="blanksby">{{cite journal | vauthors = Blanksby SJ, Ellison GB | title = Bond dissociation energies of organic molecules | journal = Accounts of Chemical Research | volume = 36 | issue = 4 | pages = 255–263 | date = April 2003 | pmid = 12693923 | doi = 10.1021/ar020230d | url = http://www.colorado.edu/chem/ellison/papers/Blanksby_Acct_Chem_Res_2003.pdf | access-date = 25 October 2017 | url-status = dead | citeseerx = 10.1.1.616.3043 | archive-url = https://web.archive.org/web/20090206144739/http://colorado.edu/chem/ellison/papers/Blanksby_Acct_Chem_Res_2003.pdf | archive-date = 6 February 2009 }}</ref>一些有机碘化合物中的碘与多个原子成键，例如可以把醇氧化成[[醛]]的[[2-碘酰基苯甲酸]]<ref>{{ OrgSynth | title = Dess–Martin periodinane: 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1''H'')-one | vauthors = Boeckman Jr RK, Shao P, Mullins JJ | year = 2000 | volume = 77 | pages = 141 | collvol = 10 | collvolpages = 696 | prep = v77p0141 | url = http://www.orgsyn.org/orgsyn/pdfs/v77p0141.pdf }}</ref>和可以氯化[[烯烃]]和[[炔烃]]的{{le|二氯化碘苯|Iodobenzene dichloride}}（PhICl<sub>2</sub>）。<ref>{{cite journal | vauthors = Jung ME, Parker MH | title = Synthesis of Several Naturally Occurring Polyhalogenated Monoterpenes of the Halomon Class(1) | journal = The Journal of Organic Chemistry | volume = 62 | issue = 21 | pages = 7094–7095 | date = October 1997 | pmid = 11671809 | doi = 10.1021/jo971371 }}</ref>

相较于有机氯化合物或有机溴化合物，有机碘化合物有两个缺点，那就是更贵和更强的毒性。<ref>{{cite web|publisher = Oxford University|title = Safety data for iodomethane|url = http://msds.chem.ox.ac.uk/IO/iodomethane.html|access-date = 2022-12-02|archive-date = 2010-08-10|archive-url = https://web.archive.org/web/20100810211004/http://msds.chem.ox.ac.uk/IO/iodomethane.html|dead-url = no}}</ref>举个例子，[[碘乙酰胺]]和[[碘乙酸]]会烷基化蛋白质中[[半胱氨酸]]残基的巯基，防止重新形成[[二硫键]]。<ref>{{cite journal | vauthors = Polgár L | title = Deuterium isotope effects on papain acylation. Evidence for lack of general base catalysis and for enzyme--leaving-group interaction | journal = European Journal of Biochemistry | volume = 98 | issue = 2 | pages = 369–374 | date = August 1979 | pmid = 488108 | doi = 10.1111/j.1432-1033.1979.tb13196.x }}</ref>

碘代烷可由[[芬克尔斯坦反应]]中的卤素交换反应产生。此反应可使用极大量的碘化物，或利用卤化物溶解度的不同而使反应向一边移动。<ref name="March">{{March6th}}</ref>在芬克尔斯坦反应中，[[碘代烷]]可由[[丙酮]]中[[氯代烷]]或[[溴代烷]]和[[碘化钠]]反应而成。碘化钠可溶于丙酮，但[[氯化钠]]和[[溴化钠]]不溶于丙酮。<ref>{{cite journal | vauthors = Ervithayasuporn V, Ervithayasuporn V, Pornsamutsin N, Pornsamutsin N, Prangyoo P, Prangyoo P, Sammawutthichai K, Sammawutthichai K, Jaroentomeechai T, Jaroentomeechai T, Phurat C, Phurat C, Teerawatananond T, Teerawatananond T | display-authors = 6 | title = One-pot synthesis of halogen exchanged silsesquioxanes: octakis(3-bromopropyl)octasilsesquioxane and octakis(3-iodopropyl)octasilsesquioxane | url = https://archive.org/details/sim_dalton-transactions_2013-10-07_42_37/page/13746 | journal = Dalton Transactions | volume = 42 | issue = 37 | pages = 13747–13753 | date = October 2013 | pmid = 23907310 | doi = 10.1039/C3DT51373D | s2cid = 41232118 }}</ref>反应由于不断生成的卤化钠沉淀，向着生成碘代烷的方向移动。<ref>{{cite journal | vauthors = Streitwieser A | year = 1956 | title = Solvolytic Displacement Reactions at Saturated Carbon Atoms | journal = [[Chem. Rev.]] | volume = 56 | pages = 571–752 | doi = 10.1021/cr50010a001 | issue = 4}}</ref><ref>{{cite journal | title = The Effect of the Carbonyl and Related Groups on the Reactivity of Halides in S<sub>N</sub>2 Reactions | vauthors = Bordwell FG, Brannen WT | journal = [[J. Am. Chem. Soc.]] | year = 1964 | volume = 86 | pages = 4645–4650 | doi = 10.1021/ja01075a025 | issue = 21}}</ref>

==含量和生产==
碘在稳定卤素当中最稀有，仅占了地壳的0.46&nbsp;[[百万分比|ppm]]（作为比较，氟544&nbsp;ppm、氯126&nbsp;ppm、溴2.5&nbsp;ppm）。{{sfn|Greenwood|Earnshaw|1997|pp=795–796}}在83种大量存在的元素（第1–42、44–60、62–83、90和92号元素）中，碘的丰度排名第61。含碘礦物較罕見，且大部分濃度夠高、足夠提供經濟上萃取價值的礦床幾乎都是[[碘酸鹽]]矿物，如[[碘鈣石]]（Ca(IO<sub>3</sub>)<sub>2</sub>）和[[碘鉻鈣石]]（7Ca(IO<sub>3</sub>)<sub>2</sub>·8CaCrO<sub>4</sub>）。{{sfn|Greenwood|Earnshaw|1997|pp=795–796}}在[[智利]]{{le|钙质层|caliche}}（主要成分为[[硝酸钠]]）的杂质中可以找到这些矿物，其中的碘含量在0.02%至1%之间。<ref name="Elzea">{{Cite book |title = Industrial Minerals & Rocks: Commodities, Markets, and Uses |publisher = SME |date = 2006 |isbn = 978-0-87335-233-8 |url = https://www.google.com/books?id=zNicdkuulE4C |pages = 541–552 |veditors = Kogel JE, Trivedi NC, Barker JM, Krukowski ST |access-date = 2022-11-28 |archive-date = 2014-02-19 |archive-url = https://web.archive.org/web/20140219173029/http://www.google.com/books?id=zNicdkuulE4C |dead-url = no }}</ref>从钙质层提取的[[碘酸钠]]会先给[[亚硫酸氢钠]]还原成碘化物，然后再和刚提取出来的碘酸盐反应生成碘单质，过滤出来。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}

钙质层是19世纪时碘的主要来源，至今仍然重要，而从[[海带]]提取碘不再经济上可行。<ref>{{Cite journal |url = https://books.google.com/books?id=wW8KAAAAIAAJ&pg=PA185 | vauthors = Stanford EC |journal = Journal of the Society of Arts |title = On the Economic Applications of Seaweed |date = 1862 |pages = 185–189}}</ref>到了20世纪末，[[卤水 (水域)|卤水]]成了可与钙质层比较的碘来源。日本[[东京]]的{{le|南关东气田|Minami Kanto gas field}}和美国[[俄克拉荷马州]]的{{le|阿纳达科盆地|Anadarko Basin}}是两个最大的卤水碘来源。这些卤水首先会纯化并用[[硫酸]]酸化，并用[[氯气]]把其中的碘化物氧化成碘单质。反应会产生碘溶液，但这个溶液较稀，需要浓缩。这些溶液会通入空气来使碘[[蒸发]]到吸收塔中，然后会用[[二氧化硫]]把碘还原成碘化氢。[[碘化氢]]之后再和氯气反应产生碘沉淀，经过滤和纯化后便可出厂。<ref name="Elzea" /><ref>{{Cite journal |journal = Geochemical Journal |volume = 40 |page = 475 |date = 2006 |title = Chemical and isotopic compositions of brines from dissolved-in-water type natural gas fields in Chiba, Japan | vauthors = Maekawa T, Igari SI, Kaneko N |doi = 10.2343/geochemj.40.475 |issue = 5 |bibcode = 2006GeocJ..40..475M|doi-access = free }}</ref>

: 2 HI + Cl<sub>2</sub> → I<sub>2</sub>↑ + 2 HCl
: I<sub>2</sub> + 2 H<sub>2</sub>O + SO<sub>2</sub> → 2 HI + H<sub>2</sub>SO<sub>4</sub>
: 2 HI + Cl<sub>2</sub> → I<sub>2</sub>↓ + 2 HCl

这些来源使得智利和日本可以成为今天碘的最大生产国。{{sfn|Greenwood|Earnshaw|1997|pp=795–796}}此外，要提取卤水中的碘还可以用[[硝酸银]]处理，使其中的碘以[[碘化银]]形式沉淀。然后，碘化银和铁反应生成[[碘化铁]]溶液，最后用[[氯气]]置换出其中的碘。{{sfn|Greenwood|Earnshaw|1997|p=799}}

== 用途 ==
碘大多用于生产有机碘化合物，有15%保持单质形式，15%以[[碘化钾]]形式使用，最后15%给制成其它无机碘化合物。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}碘化合物的主要用途包括[[催化劑]]、動物食物添加劑、[[穩定劑]]、染劑、著色劑、顏料、藥品、清潔衛生（[[碘酒]]）與照相。碘化合物的小眾用途包括除霧、[[人工降雨]]和用于分析化學。{{sfn|Greenwood|Earnshaw|1997|pp=800–4}}

===分析化学===
[[File:Testing seed for starch.jpg|thumb|用碘溶液检测种子里的淀粉]]
碘可在[[碘量法]]中检测许多物质。碘会和淀粉形成蓝色的配合物，这种配合物的产生可用于检测淀粉或碘，也是碘量法中的[[氧化还原指示剂]]。碘可用于检测钞票是不是用含有淀粉的纸做成的[[假钞]]。<ref name="Emsley">{{cite book | vauthors = Emsley J | title = Nature's Building Blocks | edition = Hardcover, First | publisher = [[Oxford University Press]] | date = 2001 | pages = [https://archive.org/details/naturesbuildingb0000emsl/page/244 244–250] | isbn = 978-0-19-850340-8 | url = https://archive.org/details/naturesbuildingb0000emsl/page/244 }}</ref>

碘常用于测定[[脂肪酸]]的不饱和度（[[碘价]]），这些不饱和度源自会和碘反应的[[双键]]。<ref>{{cite encyclopedia |first=Alfred |last=Thomas | name-list-style = vanc |title=Fats and Fatty Oils|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley-VCH |place=Weinheim |year=2002 |doi=10.1002/14356007.a10_173|isbn=3527306730 }}</ref>

[[碘化汞钾]] K<sub>2</sub>HgI<sub>4</sub>，又稱內斯勒試劑，常用於检测[[氨]]。<ref>{{citation | last = Vogel | first = Arthur I. | author2 = Svehla, G. | year = 1979 | title = Vogel's Textbook of Macro and Semimicro Qualitative Inorganic Analysis | edition = 5th | location = London | publisher = Longman | isbn = 0-582-44367-9}}</ref>类似的{{le|Mayer试剂|Mayer's reagent}}（碘化汞钾的水溶液）常给用作生物鹼的沈澱試劑。<ref>{{cite journal | last=Szász | first=György | last2=Buda | first2=László | title=Contribution to the reaction of alkaloids with potassium tetraiodomercurate | journal=Fresenius' Zeitschrift für Analytische Chemie| publisher=Springer Science and Business Media LLC | volume=253 | issue=5 | year=1971 | issn=0016-1152 | doi=10.1007/bf00426350 | pages=361–363}}</ref>碘的碱性水溶液可用于甲基酮的[[卤仿反应#應用|碘仿测试]]。<ref name="March" />

===航天器推进===
使用碘作为[[火箭推进剂]]的推进系统可变得更紧凑，重量和成本更小，且有比使用[[氙]]的离子推力器更高的运行效率。碘的[[原子量]]只比氙低3.3%，而第一和第二[[电离能]]之和就比氙低12%，这使得碘成为有前途的替代品。<ref name="ThrustMe1">{{cite journal |display-authors=6 |vauthors=Rafalskyi D, Martínez JM, Habl L, Zorzoli Rossi E, Proynov P, Boré A, Baret T, Poyet A, Lafleur T, Dudin S, Aanesland A |date=November 2021 |title=In-orbit demonstration of an iodine electric propulsion system |journal=Nature |volume=599 |issue=7885 |pages=411–415 |bibcode=2021Natur.599..411R |doi=10.1038/s41586-021-04015-y |pmc=8599014 |pmid=34789903 |quote=''Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation.''}}</ref><ref name="ThrustMe2">{{cite web |url=https://www.cnet.com/news/in-a-space-first-scientists-test-ion-thrusters-powered-by-iodine/ |title=In a space first, scientists test ion thrusters powered by iodine |vauthors=Ravisetti M |date=18 November 2021 |website=[[CNET]] |publisher=[[Red Ventures]] |access-date=2021-11-29 |archive-date=2021-11-27 |archive-url=https://web.archive.org/web/20211127105437/https://www.cnet.com/news/in-a-space-first-scientists-test-ion-thrusters-powered-by-iodine/ |dead-url=no }}</ref>

碘的使用使离子推力器变得更广泛。<ref name="ThrustMe2" />[[欧洲空间局]]称这些小但可能为颠覆性的创新可以帮助清理[[太空垃圾]]问题。通过将自己坠入大气层中燃烧，这些微型卫星在任务结束时能够轻松自毁。<ref name="ThrustMe3">{{cite web |url=https://www.esa.int/ESA_Multimedia/Images/2021/01/Iodine_thruster_used_to_change_the_orbit_of_a_small_satellite_for_the_first_time_ever#.YaUuCq-kYyQ.link |title=Iodine thruster used to change the orbit of a small satellite for the first time ever |author=<!--Not stated--> |date=22 January 2021 |website=www.esa.int |publisher=The European Space Agency |access-date=2021-11-29 |archive-date=2021-11-29 |archive-url=https://web.archive.org/web/20211129202716/https://www.esa.int/ESA_Multimedia/Images/2021/01/Iodine_thruster_used_to_change_the_orbit_of_a_small_satellite_for_the_first_time_ever#.YaUuCq-kYyQ.link |dead-url=no }}</ref>

2021年初，法国的{{le|ThrustMe}}在轨演示用于航天器的电动[[离子推进器]]。这个航天器使用碘代替氙来作为[[等离子体]]来源，以便通过用[[静电场]]加速[[离子]]来产生[[推力]]。<ref name="ThrustMe1" />

===医药===
{{Main|医疗用碘}}
====碘单质====
碘单质和含[[三碘阴离子]] I<sub>3</sub><sup>−</sup>的溶液（可由在难溶于水的碘单质的水溶液里加入[[碘化物]]而成，制备过程的逆反应可以产生碘单质）都是[[消毒剂]]。它也可用于治疗[[碘缺乏症]]。<ref name="WHO2008">{{cite book | title = WHO Model Formulary 2008 | url = https://archive.org/details/whomodelformular00unse | year = 2009 | isbn = 9789241547659 | vauthors = ((World Health Organization)) | veditors = Stuart MC, Kouimtzi M, Hill SR | hdl = 10665/44053 | author-link = World Health Organization | publisher = World Health Organization | hdl-access=free | page=[https://archive.org/details/whomodelformular00unse/page/499 499] }}</ref>

碘还可以从[[碘伏]]产生。碘伏的例子包括：<ref>{{Cite book | vauthors = Block SS |title=Disinfection, sterilization, and preservation | url = https://archive.org/details/disinfectionster0000unse_n5r4 |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |date=2001 |page=[https://archive.org/details/disinfectionster0000unse_n5r4/page/n184 159] |isbn=978-0-683-30740-5}}</ref>
* [[碘酊]]：碘的乙醇溶液，或是碘和[[碘化钠]]溶于乙醇和水的混合物而产生的溶液。
* [[卢戈氏碘液]]：碘和碘化物的水溶液，其中的碘主要以三碘化物形式存在。
* [[聚维酮碘]]
* Iodine-V：I<sub>2</sub>和{{le|黄腐酸|fulvic acid}}的[[笼形复合物]]，是可溶于水的晶体。和其它碘伏不同，Iodine-V中的碘只以I<sub>2</sub>形式存在。<ref>{{cite journal | vauthors = Köntös Z | title = Efficacy of "Essential Iodine Drops" against Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS-CoV-2) | journal = PLOS ONE | volume = 16 | issue = 7 | pages = e0254341 | date = 2021-07-09 | pmid = 34242340 | pmc = 8270147 | doi = 10.1371/journal.pone.0254341 | bibcode = 2021PLoSO..1654341K | doi-access = free }}</ref>

碘的抗菌作用迅速且在低浓度下就能起作用，因此可用于手术。<ref>{{cite journal | vauthors = Patwardhan N, Kelkar U | title = Disinfection, sterilization and operation theater guidelines for dermatosurgical practitioners in India | journal = Indian Journal of Dermatology, Venereology and Leprology | volume = 77 | issue = 1 | pages = 83–93 | date = 2011 | pmid = 21220895 | doi = 10.4103/0378-6323.74965 | doi-access = free }}</ref>碘的具体抗菌机制不明，但它会穿透微生物，攻击某些氨基酸（如[[半胱氨酸]]和[[甲硫氨酸]]）、[[核苷酸]]和[[脂肪酸]]，最终导致[[细胞死亡]]。碘也能[[抗病毒]]，但对[[细小病毒科]]的抗病毒能力要比包膜病毒弱。碘的抗病毒机制可能是攻击[[病毒包膜]]的蛋白质，并通过和包膜的脂肪酸中的碳-碳[[双键]]反应来使其不稳定。<ref name="pmid9880479">{{cite journal | vauthors = McDonnell G, Russell AD | title = Antiseptics and disinfectants: activity, action, and resistance | url = https://archive.org/details/sim_clinical-microbiology-reviews_1999-01_12_1/page/147 | journal = Clinical Microbiology Reviews | volume = 12 | issue = 1 | pages = 147–179 | date = January 1999 | pmid = 9880479 | pmc = 88911 | doi = 10.1128/CMR.12.1.147 }}</ref>

====碘化合物====
在发现有机[[螯合剂]]之前的19世纪和20世纪初，口服碘化物曾是治疗[[铅中毒]]和[[汞中毒]]的方法。<ref name=KI_en>{{cite journal|author1=Melsens, M.|author2=William Budd.|title=On the Employment of Iodide of Potassium as a Remedy for the Affections Caused by Lead and Mercury.|publisher=The British and Foreign Medico-Chirurgical Review|volume=11|date=1853|pages=201–24|pmc=5192934|pmid=30164672}}</ref>[[碘化钾]]的饱和溶液可以治疗急性[[甲状腺毒症]]。它也用于阻止甲状腺吸收[[碘-131]]（见[[#同位素]]章节）。<ref>{{cite web |url=http://hazard.com/msds/mf/baker/baker/files/p5906.htm |title=Solubility of KI in water |publisher=Hazard.com |date=1998-04-21 |access-date=2013-01-21 |archive-date=2012-04-23 |archive-url=https://web.archive.org/web/20120423195709/http://hazard.com/msds/mf/baker/baker/files/p5906.htm |dead-url=no }}</ref><ref>{{Cite web|url=http://www.eanm.org/scientific_info/guidelines/gl_radio_ther_benzyl.pdf|archive-url=https://web.archive.org/web/20090617073253/http://www.eanm.org/scientific_info/guidelines/gl_radio_ther_benzyl.pdf | title=EANM procedure guidelines for 131I-meta-iodobenzylguanidine (131I-mIBG) therapy|url-status=dead|archive-date=17 June 2009|date=17 June 2009}}</ref>

碘-131是[[放射性落下灰]]的常见成分，因甲状腺会汇集摄入的碘-131并将它们留在那里很久而特别危险。因此，有暴露于放射性落下灰中碘-131风险的人要一直服用含碘-127（没有放射性）的[[碘片]]。成年人的碘片剂量是每24小时一片130&nbsp;mg的碘片，而这片碘片可以提供100&nbsp;mg（100,000 [[微克]]）的碘。（每天的碘摄入量通常为100微克，见[[#膳食摄取量]]章节。）摄入这么大剂量的碘-127会使甲状腺饱和，最小化甲状腺吸收的碘-131。<ref>[http://www.emergency.cdc.gov/radiation/ki.asp "CDC Radiation Emergencies"] {{Wayback|url=http://www.emergency.cdc.gov/radiation/ki.asp |date=20211031123736 }}, U.S. Centers for Disease Control, 11 October 2006, accessed 14 November 2010.</ref>
[[File:Diatrizoic acid.svg|thumb|right|含碘的造影剂[[泛影酸]]]]

由于碘的高原子序和{{le|电子密度|electron density}}，以及最内层电子的[[光电效应]]，它可以吸收能量低于33.3&nbsp;keV的X射线。<ref>{{cite book | vauthors = Lancaster JL | chapter-url = http://ric.uthscsa.edu/personalpages/lancaster/DI-II_Chapters/DI_chap4.pdf | chapter = Chapter 4: Physical Determinants of Contrast | archive-url =https://web.archive.org/web/20151010172937/http://ric.uthscsa.edu/personalpages/lancaster/DI-II_Chapters/DI_chap4.pdf | archive-date=10 October 2015 | title = Physics of Medical X-Ray Imaging | publisher = The University of Texas Health Science Center }}</ref>出于这个原因，有机碘化合物常用作[[血管摄影]]和[[CT扫描]]中的X射线[[造影剂]]。至今发现的所有可溶于水的造影剂都含碘。

===其它===
碘有很大一部分都用于合成牲畜饲料的碘添加剂{{le|乙二胺二氢碘酸盐|ethylenediamine dihydroiodide}}。碘的另一大用途是[[Cativa催化法]]和[[孟山都法]]合成[[乙酸]]的催化剂。在这些乙酸合成方法中，[[氢碘酸]]会把[[甲醇]]转化成[[碘甲烷]]，后者{{le|羰基化|Carbonylation}}成[[乙酰碘]]，乙酰碘之后会水解成产物乙酸，并生成氢碘酸。<ref name=Ullmann>{{cite book | vauthors = Lyday PA, Kaiho T | chapter = Iodine and Iodine Compounds | title = Ullmann's Encyclopedia of Industrial Chemistry | date = 2015 | publisher = Wiley-VCH | location = Weinheim | doi = 10.1002/14356007.a14_381.pub2 | volume = A14 | pages = 382–390 | isbn = 9783527306732 }}</ref>

在[[晶棒法]]中，碘会和钛、锆、铪和[[钍]]反应，然后通过碘化物的分解来提纯这些金属。[[卤素灯]]也是使用类似的原理来延长灯泡的寿命。<ref>{{cite book | last=Moreira | first=Vinicius de Araujo | title=Iluminacao eletrica | publisher=Edgard Blucher | publication-place=São Paulo | date=1999 | isbn=85-212-0175-3 | oclc=46756603 | language=pt}}</ref>以前的[[攝影]][[胶卷]]使用[[碘化银]]来作為感光材料。每年都会有数吨的碘化银用于[[人工增雨]]。<ref name = Ullmann/>

有机碘化合物[[赤藓红]]是重要的食用色素。<ref name = Ullmann/>一种含碘的{{le|抑菌剂|fungistatic}}（AJ1629-34EC）可由显著抑制''{{le|Fusarium verticillioides}}''的生长，使它可能成为毒性较弱的抗真菌剂替代物。<ref name="Yates-et-al-2004">{{cite journal | vauthors = Yates IE, Arnold JW, Bacon CW, Hinton DM | title=In vitro assessments of diverse plant pathogenic fungi treated with a novel growth control agent | journal=Crop Protection| publisher=[[Elsevier]] BV | volume=23 | issue=12 | year=2004 | issn=0261-2194 | doi=10.1016/j.cropro.2004.03.019 | pages=1169–1176}}</ref>

{{sup|125}}I用作研究哪些[[配体 (生物化学)|配体]]和哪些植物[[模式识别受体]]（PRRs）结合的[[放射性示踪剂]]。<ref name="Boutrot-Zipfel-2017">{{cite journal | vauthors = Boutrot F, Zipfel C | title = Function, Discovery, and Exploitation of Plant Pattern Recognition Receptors for Broad-Spectrum Disease Resistance | journal = Annual Review of Phytopathology | volume = 55 | issue = 1 | pages = 257–286 | date = August 2017 | pmid = 28617654 | doi = 10.1146/annurev-phyto-080614-120106 | publisher = Annual Reviews}}</ref>含[[碘離子]]的母液或[[防凍劑]]能跟[[蛋白質]][[晶體]]結合，為[[X-射線繞射]]提供[[相位資訊]]<ref>{{cite book | last=Dauter | first=Miroslawa | last2=Dauter | first2=Zbigniew | title=Macromolecular Crystallography Protocols, Volume 2 | chapter=Phase Determination Using Halide Ions | publisher=Humana Press | publication-place=New Jersey | doi=10.1385/1-59745-266-1:149}}</ref>。

== 對人體的影響 ==
{{medical}}
{{main|{{le|生物学中的碘|Iodine in biology}}}}
[[File:Thyroid system.svg|thumb|upright=1.2|甲状腺激素[[三碘甲腺原氨酸|T<sub>3</sub>]]和[[四碘甲腺原氨酸|T<sub>4</sub>]]在体内的运作系统]]
碘是人體必需的[[礦物質]]，用以製造甲状腺激素[[四碘甲腺原氨酸]]和[[三碘甲腺原氨酸]]（缩写分别为T<sub>4</sub>和T<sub>3</sub>，以碘原子的数量命名）是以調控細胞代謝、神經性肌肉組織發展與成長（特別是在出生胎兒的腦部）<ref>{{cite book | last=Gropper | first=Sareen Annora Stepnick | last2=Smith | first2=Jack L. | last3=Groff | first3=James L. | title=Advanced nutrition and human metabolism | publisher=Thomson/Wadsworth | publication-place=Belmont, CA | date=2004 | isbn=0-534-55986-7 | oclc=55135458|page=468-473}}</ref>。缺碘会使T<sub>3</sub>和T<sub>4</sub>的合成量减少，且使[[甲状腺]]为了得到碘而变大，造成[[甲状腺肿]]。血液中的甲状腺激素主要由生物半衰期较长的四碘甲腺原氨酸（T<sub>4</sub>）组成，人血中T<sub>4</sub>和T<sub>3</sub>的比例在14:1到20:1之间。T<sub>4</sub>会通过{{le|脱碘酶|deiodinase}}转化成生物活性更高的T<sub>3</sub>，而T<sub>3</sub>会进一步[[脱羧]]和脱碘，生成{{le|3-碘甲状腺原胺|iodothyronamine}}（T<sub>1</sub>a）和{{le|甲状腺原胺|thyronamine}}（T<sub>0</sub>a'）。脱碘酶含有[[硒]]，因此人体合成T<sub>3</sub>需要硒。<ref>{{cite web|url=http://emedicine.medscape.com/article/819692-overview#showall|vauthors=Irizarry L|title=Thyroid Hormone Toxicity|website=Medscape|publisher=WedMD LLC|date=23 April 2014|access-date=2 May 2014|archive-date=2021-10-31|archive-url=https://web.archive.org/web/20211031132146/https://emedicine.medscape.com/article/819692-overview#showall|dead-url=no}}</ref>

碘占了T<sub>4</sub>分子量的65%，以及T<sub>3</sub>分子量的59%。有15–20&nbsp;mg的碘储存在甲状腺中，而70%的碘存在于其它组织中，包括乳腺、眼睛、胃粘膜、胎儿胸腺、脑脊髓液和脉络丛、动脉壁、宫颈和唾液腺。在这些组织中，碘化物会通过{{le|钠碘同向运输蛋白|sodium-iodide symporter}}（NIS）直接进入细胞。乳腺组织中的碘与胎儿和新生儿发育有关，但碘在其它组织的作用仍有不明确的地方。<ref name="Patrick2008" />

=== 膳食摄取量 ===
[[美国国家医学院]]推荐的碘摄入量为一岁以下婴儿110~130 [[微克|µg]]，1~8岁儿童90&nbsp;µg，9~13岁儿童120&nbsp;µg，成年人150&nbsp;µg，孕妇220&nbsp;µg，哺乳期妇女290&nbsp;µg。<ref name="lpi" /><ref>{{cite web|url=http://iom.edu/en/Global/News%20Announcements/~/media/Files/Activity%20Files/Nutrition/DRIs/DRISummaryListing2.ashx |archive-url=https://web.archive.org/web/20091030004039/http://iom.edu/en/Global/News%20Announcements/~/media/Files/Activity%20Files/Nutrition/DRIs/DRISummaryListing2.ashx |url-status=dead |archive-date=30 October 2009 |title=Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals, Vitamins |publisher=[[Institute of Medicine]] |date=2004 |access-date=9 June 2010 }}</ref>成年人对碘的可耐受最高摄入量（UL）为每天1,100&nbsp;μg<ref name="InstituteofMedicine">{{Cite book| author = United States National Research Council| date = 2000| title = Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc| pages = 258–259| publisher = National Academies Press| url = http://books.nap.edu/openbook.php?record_id=10026&page=258| doi = 10.17226/10026| pmid = 25057538| isbn = 978-0-309-07279-3| access-date = 2022-12-02| archive-date = 2015-07-25| archive-url = https://web.archive.org/web/20150725203752/http://books.nap.edu/openbook.php?record_id=10026&page=258| dead-url = no}}</ref>，此上限是通过分析补充剂对[[促甲状腺激素]]的影响而定的。<ref name="Patrick2008" />

甲状腺合成一天的T<sub>4</sub>和T<sub>3</sub>不需要超过70&nbsp;μg的碘。<ref name="lpi" />超过这个值的推荐碘摄入量用来使许多身体系统，包括[[胃黏膜]]、[[唾液腺]]、脑细胞、[[脉络丛]]、[[胸腺]]和[[动脉]]壁保持最佳状态。<ref name="lpi" /><ref>{{cite journal | vauthors = Venturi S, Venturi M | title = Iodine, thymus, and immunity | journal = Nutrition | volume = 25 | issue = 9 | pages = 977–979 | date = September 2009 | pmid = 19647627 | doi = 10.1016/j.nut.2009.06.002 }}</ref><ref>{{cite journal | vauthors = Ullberg S, Ewaldsson B | title = Distribution of radio-iodine studied by whole-body autoradiography | url = https://archive.org/details/sim_acta-radiologica_1964-02_2_1/page/24 | journal = Acta Radiologica | volume = 2 | pages = 24–32 | date = February 1964 | pmid = 14153759 | doi = 10.3109/02841866409134127 }}</ref><ref name="Venturi, Sebastiano 2014 185–205">{{Cite journal| vauthors = Venturi S |title=Iodine, PUFAs and Iodolipids in Health and Disease: An Evolutionary Perspective|journal=Human Evolution|volume= 29 |issue= 1–3|pages=185–205|year=2014|issn=0393-9375}}</ref>

碘的天然食物来源包括[[海产]]（如鱼、[[海带]]和[[贝类]]）、乳制品和[[蛋]]。<ref>{{cite web| publisher =Iodine Global Network|url =http://ign.org/p142002146.html|archive-url=https://web.archive.org/web/20150813130042/http://ign.org/p142002146.html|archive-date=13 August 2015|title=Where do we get iodine from?|url-status=live}}</ref><ref name = medlineplus002421/>[[含碘食盐]]中加入了[[碘化钠]]来增加碘含量。<ref name="medlineplus002421">{{cite encyclopedia| url = https://www.nlm.nih.gov/medlineplus/ency/article/002421.htm| title = Iodine in diet| encyclopedia = MedlinePlus Medical Encyclopedia| access-date = 2022-12-02| archive-date = 2016-07-05| archive-url = https://web.archive.org/web/20160705122918/https://www.nlm.nih.gov/medlineplus/ency/article/002421.htm| dead-url = no}}</ref><ref name="American Thyroid Association">{{cite web|title=American Thyroid Association|url=http://www.thyroid.org/iodine-deficiency/|work=thyroid.org|publisher=American Thyroid Association|access-date=4 April 2014|archive-date=2023-08-03|archive-url=https://web.archive.org/web/20230803045045/https://www.thyroid.org/iodine-deficiency/|dead-url=no}}</ref>

2000年，美国男人和女人的碘摄入量中位数分别为每天240–300&nbsp;μg和190–210&nbsp;μg。<ref name="InstituteofMedicine" />美国人的碘摄入量足够，<ref>{{cite journal | vauthors = Caldwell KL, Makhmudov A, Ely E, Jones RL, Wang RY | title = Iodine status of the U.S. population, National Health and Nutrition Examination Survey, 2005–2006 and 2007–2008 | journal = Thyroid | volume = 21 | issue = 4 | pages = 419–427 | date = April 2011 | pmid = 21323596 | doi = 10.1089/thy.2010.0077 | url = https://zenodo.org/record/1235283 | access-date = 2022-12-02 | archive-date = 2022-12-02 | archive-url = https://web.archive.org/web/20221202135223/https://zenodo.org/record/1235283 | dead-url = no }}</ref><ref name="Lueng">{{cite journal | vauthors = Leung AM, Braverman LE, Pearce EN | title = History of U.S. iodine fortification and supplementation | journal = Nutrients | volume = 4 | issue = 11 | pages = 1740–1746 | date = November 2012 | pmid = 23201844 | pmc = 3509517 | doi = 10.3390/nu4111740 | doi-access = free }}</ref>而育龄妇女和孕妇可能有轻微的碘缺乏症风险。<ref name="Lueng" />有认为日本人源自{{le|昆布|Kombu}}<ref name="Patrick2008">{{cite journal | vauthors = Patrick L | title = Iodine: deficiency and therapeutic considerations | journal = Alternative Medicine Review | volume = 13 | issue = 2 | pages = 116–127 | date = June 2008 | pmid = 18590348 | url = http://www.thorne.com/altmedrev/.fulltext/13/2/116.pdf | url-status = dead | archive-url = https://web.archive.org/web/20130531112100/http://www.thorne.com/altmedrev/.fulltext/13/2/116.pdf | archive-date = 31 May 2013 }}</ref>的碘摄入量很高，达到每天5,280–13,800&nbsp;μg，但最新研究表明日本人的实际碘摄入量更接近于每天1,000–3,000&nbsp;μg。<ref>{{cite journal | vauthors = Zava TT, Zava DT | title = Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis | journal = Thyroid Research | volume = 4 | pages = 14 | date = October 2011 | pmid = 21975053 | pmc = 3204293 | doi = 10.1186/1756-6614-4-14 }}</ref>日本成年人的可耐受最高摄入量在2015年最后修改成了每天3,000&nbsp;µg。<ref>{{cite web |title=Overview of Dietary Reference Intakes for Japanese (2015) |publisher=Minister of Health, Labour and Welfare, Japan |url=http://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/Overview.pdf |access-date=14 March 2022 |archive-date=2021-04-23 |archive-url=https://web.archive.org/web/20210423083531/https://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/Overview.pdf |dead-url=no }}</ref>在食盐加碘等碘营养强化计划执行后发生一些由碘引起的[[甲亢]]病例（{{le|Jod-Basedow现象|Jod-Basedow phenomenon}}）。这种情况似乎主要发生在40岁以上的人群中，当碘缺乏症严重且碘摄入量突然剧增时，风险似乎更高。<ref>{{cite journal | vauthors = Wu T, Liu GJ, Li P, Clar C | title = Iodised salt for preventing iodine deficiency disorders | journal = The Cochrane Database of Systematic Reviews | volume = 2010 | issue = 3 | pages = CD003204 | date = 2002 | pmid = 12137681 | pmc = 9006116 | doi = 10.1002/14651858.CD003204 | veditors = Wu T }}</ref>

=== 缺乏 ===
{{main|碘缺乏症}}
当一个人的尿碘低于100μg/L时，他就患上了碘缺乏症。<ref>{{cite book | last=De Benoist | first=Bruno | author2=World Health Organization. Nutrition for Health and Development | title=Iodine status worldwide : WHO global database on iodine deficiency | publisher=Dept. of Nutrition for Health and Development, World Health Organization | publication-place=Geneva | date=2004 | isbn=978-92-4-159200-0 | oclc=58790071}}</ref>在饮食中碘含量较少的地区（如没有海产的偏远内陆地区和半干旱气候地区）生活的人较易得碘缺乏症。<ref name="Dissanayake">{{Cite journal| vauthors = Dissanayake CB, Chandrajith R, Tobschall HJ |title = The iodine cycle in the tropical environment – implications on iodine deficiency disorders|journal = International Journal of Environmental Studies|volume = 56 |page= 357| doi = 10.1080/00207239908711210|date = 1999|issue = 3}}</ref>[[碘缺乏症]]会导致[[甲状腺机能低下症]]，它的症状为极度疲劳、[[甲状腺肿]]、智力减退、抑郁、体重增加和基础体温下降。<ref>{{Cite book|chapter = Endemic Goiter|title = Endocrinology & metabolism|vauthors = Felig P, Frohman LA|publisher = McGraw-Hill Professional|date = 2001|isbn = 978-0-07-022001-0|chapter-url = https://books.google.com/books?id=AZUUGrp6yUgC&pg=RA1-PA351|access-date = 2022-12-02|archive-date = 2023-01-12|archive-url = https://web.archive.org/web/20230112212836/https://books.google.com/books?id=AZUUGrp6yUgC&pg=RA1-PA351|dead-url = no}}</ref>婴儿和小孩因缺碘而导致甲状腺功能减退造成的碘缺乏症是可避免的[[智能障碍]]的主因。发达国家采用食盐加碘的方法解决了该问题，但碘缺乏症在发展中国家里仍是严重的公共卫生问题。<ref>{{cite web|url =https://www.who.int/nutrition/topics/idd/en/|archive-url =https://web.archive.org/web/20060930020824/http://www.who.int/nutrition/topics/idd/en/|url-status =dead|archive-date =30 September 2006|title = Micronutrient deficiency: iodine deficiency disorders|publisher = WHO}}</ref>给中度缺碘儿童补充碘可改善他们的信息处理、精细动作技能和视觉问题解决能力。<ref>{{cite journal | vauthors = Zimmermann MB, Connolly K, Bozo M, Bridson J, Rohner F, Grimci L | title = Iodine supplementation improves cognition in iodine-deficient schoolchildren in Albania: a randomized, controlled, double-blind study | url = https://archive.org/details/sim_american-journal-of-clinical-nutrition_2006-01_83_1/page/108 | journal = The American Journal of Clinical Nutrition | volume = 83 | issue = 1 | pages = 108–114 | date = January 2006 | pmid = 16400058 | doi = 10.1093/ajcn/83.1.108 | doi-access = free }}</ref>

==危害==
===毒性===
{{Chembox
| ImageFile = Sample_of_iodine.jpg
| Section7 = {{Chembox Hazards
| ExternalSDS =
| GHSPictograms = {{GHS07}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|312|332|315|319|335|372|400}}
| PPhrases = {{P-phrases|261|273|280|305|351|338|314}}<ref>{{Cite web|url=https://www.sigmaaldrich.com/catalog/product/sigald/207772|title=Iodine 207772|website=I2|access-date=2022-11-28|archive-date=2024-03-19|archive-url=https://web.archive.org/web/20240319070756/https://www.sigmaaldrich.com/US/en/product/sigald/207772|dead-url=no}}</ref>
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = 
 }}
}}
口服未稀释的碘单质（I<sub>2</sub>）[[有毒]]，对成年人的致死量为30&nbsp;mg/kg，也就是对于体重70–80&nbsp;kg的人来说2.1–2.4克的碘即可致死。（尽管对大鼠的实验显示它们食用14000&nbsp;mg/kg的碘后仍能生存<ref>{{cite journal | last=Ilin | first=Alexander | last2=Nersesyan | first2=Armen | title=Toxicology of iodine: A mini review | journal=Archive of Oncology | volume=21 | issue=2 | date=2013 | issn=0354-7310 | doi=10.2298/AOO1302065I | pages=65–71}}</ref>）过量的碘在{{le|硒缺乏症|selenium deficiency|缺硒}}时的[[细胞毒性]]更强，<ref>{{cite journal | vauthors = Smyth PP | title = Role of iodine in antioxidant defence in thyroid and breast disease | journal = BioFactors | volume = 19 | issue = 3–4 | pages = 121–130 | year = 2003 | pmid = 14757962 | doi = 10.1002/biof.5520190304 | s2cid = 7803619 }}</ref>因此给缺乏硒的人碘补充剂理论上有害。<ref name="Patrick2008" />碘的毒性源自于其氧化性，会使蛋白质和酶变性。<ref>{{cite web |url=http://butane.chem.uiuc.edu/cyerkes/chem104A_S07/Lecture_Notes_104/lect29c.html |title=Lecture 29: Protein Structure and Denaturation |vauthors=Yerkes C |date=2007 |website=chem.uiuc.edu |publisher=University of Illinois |access-date=23 October 2016 |archive-date=2022-03-31 |archive-url=https://web.archive.org/web/20220331110145/http://butane.chem.uiuc.edu/cyerkes/chem104A_S07/Lecture_Notes_104/lect29c.html |dead-url=no }}</ref>

碘单质会刺激皮肤，直接接触会造成伤害，因此碘晶体需要小心处理。长时间接触像是[[碘酊]]和[[卢戈氏碘液]]的浓碘溶液会损害皮肤。有报告残留在皮肤上的[[聚维酮碘]]导致灼伤的案例。<ref name="Lowe">{{cite journal | vauthors = Lowe DO, Knowles SR, Weber EA, Railton CJ, Shear NH | title = Povidone-iodine-induced burn: case report and review of the literature | url = https://archive.org/details/sim_pharmacotherapy_2006-11_26_11/page/1641 | journal = Pharmacotherapy | volume = 26 | issue = 11 | pages = 1641–1645 | date = November 2006 | pmid = 17064209 | doi = 10.1592/phco.26.11.1641 | s2cid = 25708713 }}</ref>

==== 工作暴露====
工作场所里的人会通过吸入、摄入、皮肤和眼睛接触碘。[[美国职业安全与健康管理局]]把碘的[[允许最大暴露限值]]定为0.1 ppm（1&nbsp;mg/m<sup>3</sup>），而[[美国国家职业安全卫生研究所]]也把碘的{{le|建议暴露限值|Recommended exposure limit}}定为0.1&nbsp;ppm（1&nbsp;mg/m<sup>3</sup>）。碘的浓度达到2 ppm时就会{{le|立即危及生命或健康|IDLH}}。<ref>{{Cite web|title = CDC - NIOSH Pocket Guide to Chemical Hazards - Iodine|url = https://www.cdc.gov/niosh/npg/npgd0342.html|website = cdc.gov|access-date = 2015-11-06|archive-date = 2022-11-29|archive-url = https://web.archive.org/web/20221129024702/https://www.cdc.gov/niosh/npg/npgd0342.html|dead-url = no}}</ref>

====过敏====
一些人会对含碘产品和食物[[过敏]]，他们接触到碘酊或聚维酮碘时会起红疹。<ref name="dermnet">{{Cite web |title=Iodine |url=https://dermnetnz.org/topics/iodine |website=DermNet® |date=2023-10-26 |language=en |access-date=2025-03-09}}</ref>他们使用含碘造影剂时可能也会让他们起红疹，甚至可致命的[[过敏性休克]]。这些过敏反应使人误解这些人会对碘单质过敏，甚至对富含碘的海鲜过敏的人也可以这样解释。<ref>{{cite journal |vauthors=Boehm I |title=Seafood allergy and radiocontrast media: are physicians propagating a myth? |journal=The American Journal of Medicine |date=August 2008 |volume=121 |issue=8 |pages=e19 |doi=10.1016/j.amjmed.2008.03.035 |pmid=18691465}}</ref>理论上，由于人不可能对碘单质或简单碘化物过敏，因此没有真正对碘过敏的人。对含碘产品和食物过敏显然与其它成分有关，因此对一种含碘食物或产品过敏的人可能不会对另一种食物或产品产生过敏反应。对各种食物（贝类、鸡蛋、牛奶等）过敏的患者不会增加对造影剂过敏的风险。<ref name="pmid31153557">{{cite journal |vauthors=Lombardo P, Nairz K, Boehm I |title=Patients' safety and the "iodine allergy" - How should we manage patients with iodine allergy before they receive an iodinated contrast medium? |journal=European Journal of Radiology |date=July 2019 |volume=116 |issue=7 |pages=150–151 |doi=10.1016/j.ejrad.2019.05.002 |pmid=31153557 |s2cid=164898934}}</ref><ref name="ucsf">{{Cite web |title=CT and X-ray Contrast Guidelines |url=https://radiology.ucsf.edu/patient-care/patient-safety/contrast/iodinated#accordion-allergies-and-premedication |website=UCSF Radiology |date=2010-04-07 |language=en |access-date=2025-03-09}}</ref>与所有药物一样，在给予任何含碘药物前，应询问和咨询患者的过敏史。<ref>{{Cite journal |vauthors=Katelaris C |title='Iodine Allergy' label is misleading |journal=Australian Prescriber |date=2009 |volume=32 |issue=5 |pages=125–128 |doi=10.18773/austprescr.2009.061 |doi-access=free}}</ref>

===美国缉毒局第一类化学品===
[[磷]]可以把碘还原成[[氢碘酸]]，而氢碘酸则可以把[[麻黄碱]]或[[伪麻黄碱]]还原成[[冰毒]]。<ref>{{Cite journal| vauthors = Skinner HF |date = 1990|title = Methamphetamine synthesis via hydriodic acid/red phosphorus reduction of ephedrine| url = https://archive.org/details/sim_forensic-science-international_1990-12_48_2/page/123 |journal = Forensic Science International|volume = 48|issue = 2|pages = 123–134|doi = 10.1016/0379-0738(90)90104-7}}</ref>出于这个原因，[[美国缉毒局]]归类碘为[[美国缉毒局化学品监控列表#第一类化学品|第一类化学品]]。<ref>{{Cite web | url=https://www.deadiversion.usdoj.gov/21cfr/cfr/1310/1310_02.htm | title=PART 1310 - Section 1310.02 Substances covered | access-date=5 December 2019 | archive-date=17 October 2017 | archive-url=https://web.archive.org/web/20171017090223/https://www.deadiversion.usdoj.gov/21cfr/cfr/1310/1310_02.htm | url-status=dead }}</ref>

== 參見 ==
*[[氫碘酸]] 
*[[碘化氫]] 
*[[碘酸]]
*[[醫療用碘]]

== 参考资料 ==
{{Reflist|30em}}

==参考书目==
{{refbegin}}
*{{cite book
 |last1=Greenwood |first1=Norman  N.
 |last2=Earnshaw |first2=Alan
 |year=1997
 |title=Chemistry of the Elements
 |edition=2nd
 |publisher=Butterworth-Heinemann
 |isbn=978-0-08-037941-8
 |ref=harv
}}
{{refend}}

==外部連結==
{{Elements.links|I|53}}
{{17族元素|I}}
{{Diatomicelements}}
{{Authority control}}

{{GA}}

[[Category:碘| ]]
[[Category:化学元素|5Q]]
[[Category:第5周期元素|5Q]]
[[Category:卤素]]
[[Category:反应性非金属元素]]
[[Category:双原子非金属元素]]
[[Category:膳食矿物质]]
[[Category:氧化剂]]
[[Category:有色气体]]
[[Category:營養學]]
[[Category:生命化学元素]]
[[Category:世界卫生组织基本药物]]