编辑“︁镭”︁（章节）

==性质==
镭是已知最重的[[碱土金属]]，也是唯一的[[放射性]]碱土金属。它的物理和化学性质与[[同类物]][[钡]]最接近。{{sfn|Greenwood|Earnshaw|1997|p=112}}

纯镭为[[金属活动性|活泼]]金属，色泽为银白色，与同族的[[钙]]、[[锶]]、[[钡]]不同（三者均为淡黄色）。{{sfn|Greenwood|Earnshaw|1997|p=112}}镭在空气中會迅速褪色，形成黑色的[[氮化镭]]（Ra<sub>3</sub>N<sub>2</sub>）。{{sfn|Kirby et al.|p=4}}镭的[[熔点]]为{{convert|700|°C}}或{{convert|960|°C}}{{efn|这两个数值都有来源，科学家们对镭的熔点的真实数值并没有达成一致。{{sfn|Kirby et al.|p=4}}}}，[[沸点]] {{convert|1737|°C}}。这两个数值都低于钡，符合碱土金属的[[元素周期律]]。<ref name="Lide2004">{{cite book|last = Lide|first=D. R. |title = CRC Handbook of Chemistry and Physics |url = https://archive.org/details/crchandbookofche81lide|url-access = registration|edition = 84th |location = Boca Raton (FL) |publisher = CRC Press |date = 2004 |isbn = 978-0-8493-0484-2}}</ref>类似钡和[[碱金属]]，镭在[[标准情况]]下的晶体结构是[[立方晶系]]，其中的镭-镭距离是514.8[[皮米]]。<ref>{{cite journal | last1 = Weigel | first1 = F. | last2 = Trinkl | first2 = A. | year = 1968 | title = Zur Kristallchemie des Radiums| doi = 10.1524/ract.1968.10.12.78 | journal = Radiochim. Acta | volume = 10 | issue = 1–2| page = 78| s2cid = 100313675 }}</ref>镭的密度是5.5&nbsp;g/cm<sup>3</sup>，高于钡，符合元素周期律。由于镭和钡的晶体结构相似，<ref name=Young/><ref>[http://wwwhomes.uni-bielefeld.de/achim/ele_structures.html "Crystal Structures of the Chemical Elements at 1 bar"] {{Webarchive|url=https://web.archive.org/web/20140826161012/http://wwwhomes.uni-bielefeld.de/achim/ele_structures.html |date=26 August 2014 }}. uni-bielefeld.de.</ref><!--books.google.com/books?id=QsgmAAAAMAAJ&q="melting+point+of+radium"&dq="melting+point+of+radium"&hl=de&sa=X&ei=8j_iT72ZAYfOsgb-r91v&ved=0CD4Q6AEwAg books.google.com/books?id=1hNSAAAAMAAJ&q="melting+point+of+radium"&dq="melting+point+of+radium"&hl=de&sa=X&ei=8j_iT72ZAYfOsgb-r91v&ved=0CEgQ6AEwBA-->镭和钡的密度比与镭和钡的原子质量比类似。<ref name=Young>{{cite book|chapter-url=https://books.google.com/books?id=F2HVYh6wLBcC&pg=PA85|page=85|chapter=Radium|author=Young, David A.|title=Phase Diagrams of the Elements|publisher=University of California Press|date=1991|isbn=978-0-520-91148-2|access-date=2021-08-04|archive-date=2022-05-21|archive-url=https://web.archive.org/web/20220521043109/https://books.google.com/books?id=F2HVYh6wLBcC&pg=PA85}}</ref>