编辑“︁铊”︁（章节）

==性質==
鉈金屬非常軟，可[[延展性]]很高，在室溫下可以用刀切割。它具有金屬光澤，但在接觸[[空氣]]之後，會變為藍灰色，與[[鉛]]相似。長期置於空氣中的鉈會形成厚厚的氧化表層。要保存它的光澤，可以將其浸泡在油裡。當接觸水後，會形成氫氧化鉈。硫酸和[[硝酸]]能快速溶解鉈，分別形成[[硫酸亞鉈]]和[[硝酸亞鉈]]，而[[盐酸]]則會使鉈表面形成一層不可溶的[[氯化鉈]]。<ref name="HollemanAF">{{cite book|publisher = Walter de Gruyter|year = 1985|edition = 91–100|pages = 892–893|isbn = 3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first = Arnold F.|last = Holleman|coauthors = Wiberg, Egon; Wiberg, Nils|chapter =Thallium|language = de}}</ref>Tl<sup>+</sup>/Tl的[[標準電極電勢]]為−0.34V，比[[鐵]]的−0.44V稍低。

===同位素===
{{main|鉈的同位素}}
鉈共有41種[[同位素]]，[[質量數]]介乎176和216之間，其中<sup>203</sup>Tl和<sup>205</sup>Tl是[[稳定同位素]]。<sup>205</sup>Tl是自然界中[[錼衰變鏈]]的最終產物，不過其母同位素[[鉍-209|<sup>209</sup>Bi]]的[[半衰期]]極長，超過[[宇宙年齡]]的十億倍。<ref name="Kean">{{cite book|last=Kean|first=Sam|title=The Disappearing Spoon (and other true tales of madness, love, and the history of the world from the Periodic Table of Elements)|url=https://archive.org/details/disappearingspoo0000kean_p8o5|publisher=Back Bay Books |location=New York/Boston|year=2011|pages=[https://archive.org/details/disappearingspoo0000kean_p8o5/page/158 158]–160|isbn=978-0-316-051637}}</ref>

<sup>204</sup>Tl（半衰期3.78年）是鉈最長壽的[[放射性同位素]]，<ref name="Audi">{{cite journal| last = Audi|first = Georges|title = The NUBASE Evaluation of Nuclear and Decay Properties|journal = Nuclear Physics A|volume = 729| issue = 1|pages = 3–128| publisher = Atomic Mass Data Center|year = 2003| doi=10.1016/j.nuclphysa.2003.11.001| bibcode=2003NuPhA.729....3A| last2 = Bersillon| first2 = O.| last3 = Blachot| first3 = J.| last4 = Wapstra| first4 = A.H.}}</ref>可以在[[核反應爐]]中對鉈的穩定同位素[[中子活化]]製成。<ref name="Audi"/><ref>{{cite web|url = http://www-pub.iaea.org/MTCD/publications/PDF/te_1340_web.pdf|title = Manual for reactor produced radioisotopes|publisher = [[國際原子能機構|International Atomic Energy Agency]]|year = 2003|accessdate = 2010-05-13|archive-date = 2011-05-21|archive-url = https://web.archive.org/web/20110521072530/http://www-pub.iaea.org/MTCD/publications/PDF/te_1340_web.pdf|dead-url = yes}}</ref>

<sup>202</sup>Tl（半衰期12.23天）可以在[[迴旋加速器]]中合成。<ref>{{cite web|url = http://hss.energy.gov/healthsafety/ohre//roadmap/histories/0472/0472d.html|title = Thallium Research|publisher = United States Department of Energy|accessdate = 2010-05-13|deadurl = yes|archiveurl = https://web.archive.org/web/20090413195931/http://hss.energy.gov/healthsafety/ohre//roadmap/histories/0472/0472d.html|archivedate = 2009-04-13}}</ref>

<sup>201</sup>Tl（半衰期73小時）會以[[電子捕獲]]的方式衰變，並釋放[[X射線]]（能量約为70至80&nbsp;[[電子伏特|keV]]）以及總豐度為10%、能量分別為135和167&nbsp;keV的[[光子]]。<ref name="Audi"/>它既能提供良好的示蹤效果，又不會使病人承受過大的輻射劑量，所以是核醫學成像的理想示蹤劑。它是鉈元素核子[[心脏压力测试]]中最常用的同位素。<ref>{{cite book|url = http://books.google.com/?id=CqQgnHrDxrUC&pg=PA173|chapter = Detection, Evaluation, and Risk Stratification of Coronary Artery Disease by Thallium-201 Myocardial Perfusion Scintigraphy 155|first1 = Jamshid|last1 = Maddahi|first2 = Daniel|last2 =Berman|title = Cardiac SPECT imaging|edition = 2|publisher = Lippincott Williams & Wilkins|year = 2001|isbn = 978-0-7817-2007-6|pages = 155–178}}</ref>

<sup>208</sup>Tl（半衰期3.05分鐘）是[[釷]][[衰變鏈]]的自然產物之一。它所釋放的2615&nbsp;keV[[伽馬射線]]是自然[[背景輻射]]中的一大主要高能特徵。

===化學性質===
{{Category see also|鉈化合物}}
鉈的兩個主要[[氧化態]]為+1和+3。當處於+1態時，鉈化合物和[[鉀]]或[[銀]]的化合物十分相近，因此在元素剛被發現後不久，一些[[歐洲]]化學家（[[英國]]除外）曾把它當做[[鹼金屬]]。<ref>{{cite journal |last1=Crookes |first1=William |year=1864 |title=On Thallium |journal=The Journal of the Chemical Society, London |volume=XVII |issue= |pages=112–152 |publisher=Harrison & Sons |url=http://books.google.com/books?id=H58wAAAAYAAJ |accessdate=January 13, 2012 |doi=10.1039/js8641700112 |archive-date=2014-07-01 |archive-url=https://web.archive.org/web/20140701065003/http://books.google.com/books?id=H58wAAAAYAAJ |dead-url=no }}</ref>{{rp|126}}

氧化態為+3的化合物與相對應的鋁(III)化合物相似。Tl(III)具有較高的氧化性，如Tl<sup>3+</sup> + 3 e<sup>–</sup> → Tl(''s'')反應的還原電勢為+0.72&nbsp;V。[[氧化鉈]]是一種黑色固體，在800&nbsp;°C以上溫度會分解，形成[[氧化亞鉈]]和[[氧氣]]。<ref name="HollemanAF"/>