Editing Strontium (section)

==Characteristics==
[[File:Strontium 1.jpg|thumb|left|upright|Oxidized [[Dendrite (crystal)|dendritic]] strontium]]

Strontium is a [[divalent]] silvery metal with a pale yellow tint whose properties are mostly intermediate between and similar to those of its group neighbors [[calcium]] and [[barium]].<ref name="Greenwood112">Greenwood and Earnshaw, pp. 112–13</ref> It is softer than calcium and harder than barium. Its melting (777&nbsp;°C) and boiling (1377&nbsp;°C) points are lower than those of calcium (842&nbsp;°C and 1484&nbsp;°C respectively); barium continues this downward trend in the melting point (727&nbsp;°C), but not in the boiling point (1900&nbsp;°C). The density of strontium (2.64&nbsp;g/cm<sup>3</sup>) is similarly intermediate between those of calcium (1.54&nbsp;g/cm<sup>3</sup>) and barium (3.594&nbsp;g/cm<sup>3</sup>).<ref name="CRC">C. R. Hammond ''The elements'' (pp. 4–35) in {{RubberBible86th}}</ref> Three [[Allotropy|allotropes]] of metallic strontium exist, with [[transition point]]s at 235 and 540&nbsp;°C.{{cn|date=September 2023}}

The [[standard electrode potential]] for the Sr<sup>2+</sup>/Sr couple is −2.89&nbsp;V, approximately midway between those of the Ca<sup>2+</sup>/Ca (−2.84&nbsp;V) and Ba<sup>2+</sup>/Ba (−2.92&nbsp;V) couples, and close to those of the neighboring [[alkali metal]]s.<ref name="Greenwood111" /> Strontium is intermediate between calcium and barium in its reactivity toward water, with which it reacts on contact to produce [[strontium hydroxide]] and [[hydrogen]] gas. Strontium metal burns in air to produce both [[strontium oxide]] and [[strontium nitride]], but since it does not react with [[nitrogen]] below 380&nbsp;°C, at room temperature it forms only the oxide spontaneously.<ref name="CRC" /> Besides the simple oxide SrO, the [[peroxide]] SrO<sub>2</sub> can be made by direct oxidation of strontium metal under a high pressure of oxygen, and there is some evidence for a yellow [[superoxide]] Sr(O<sub>2</sub>)<sub>2</sub>.<ref>Greenwood and Earnshaw, p. 119</ref> [[Strontium hydroxide]], Sr(OH)<sub>2</sub>, is a strong base, though it is not as strong as the hydroxides of barium or the alkali metals.<ref>Greenwood and Earnshaw, p. 121</ref> All four dihalides of strontium are known.<ref>Greenwood and Earnshaw, p. 117</ref>

Due to the large size of the heavy [[s-block]] elements, including strontium, a vast range of [[coordination number]]s is known, from 2, 3, or 4 all the way to 22 or 24 in SrCd<sub>11</sub> and SrZn<sub>13</sub>. The Sr<sup>2+</sup> ion is quite large, so that high coordination numbers are the rule.<ref>Greenwood and Earnshaw, p. 115</ref> The large size of strontium and barium plays a significant part in stabilising strontium complexes with [[denticity|polydentate]] [[macrocycle|macrocyclic]] ligands such as [[crown ether]]s: for example, while [[18-crown-6]] forms relatively weak complexes with calcium and the alkali metals, its strontium and barium complexes are much stronger.<ref>Greenwood and Earnshaw, p. 124</ref>

Organostrontium compounds contain one or more strontium–carbon bonds. They have been reported as intermediates in [[Barbier reaction|Barbier-type]] reactions.<ref>{{Cite journal| doi = 10.1246/bcsj.77.341| title = The Barbier-Type Alkylation of Aldehydes with Alkyl Halides in the Presence of Metallic Strontium| year = 2004| last1 = Miyoshi | first1 = N.| last2 = Kamiura | first2 = K.| last3 = Oka | first3 = H.| last4 = Kita | first4 = A.| last5 = Kuwata | first5 = R.| last6 = Ikehara | first6 = D.| last7 = Wada | first7 = M.| journal = Bulletin of the Chemical Society of Japan| volume = 77| issue = 2| page = 341 }}</ref><ref>{{Cite journal| doi = 10.1246/cl.2005.760| title = The Chemistry of Alkylstrontium Halide Analogues: Barbier-type Alkylation of Imines with Alkyl Halides| year = 2005| last1 = Miyoshi | first1 = N.| last2 = Ikehara | first2 = D.| last3 = Kohno | first3 = T.| last4 = Matsui | first4 = A.| last5 = Wada | first5 = M.| journal = Chemistry Letters| volume = 34| issue = 6| page = 760 }}</ref><ref>{{Cite journal| doi = 10.1002/ejoc.200500484| title = The Chemistry of Alkylstrontium Halide Analogues, Part 2: Barbier-Type Dialkylation of Esters with Alkyl Halides| year = 2005| last1 = Miyoshi | first1 = N.| last2 = Matsuo | first2 = T.| last3 = Wada | first3 = M.| journal = European Journal of Organic Chemistry| volume = 2005| issue = 20| page = 4253 }}</ref> Although strontium is in the same group as magnesium, and [[organomagnesium compound]]s are very commonly used throughout chemistry, organostrontium compounds are not similarly widespread because they are more difficult to make and more reactive. Organostrontium compounds tend to be more similar to organo[[europium]] or organo[[samarium]] compounds due to the similar [[ionic radius|ionic radii]] of these elements (Sr<sup>2+</sup> 118&nbsp;pm; Eu<sup>2+</sup> 117&nbsp;pm; Sm<sup>2+</sup> 122&nbsp;pm). Most of these compounds can only be prepared at low temperatures; bulky ligands tend to favor stability. For example, strontium di[[cyclopentadienyl]], Sr(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>, must be made by directly reacting strontium metal with [[mercurocene]] or [[cyclopentadiene]] itself; replacing the C<sub>5</sub>H<sub>5</sub> ligand with the bulkier C<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub> ligand on the other hand increases the compound's solubility, volatility, and kinetic stability.<ref>Greenwood and Earnshaw, pp. 136–37</ref>

Because of its extreme reactivity with [[oxygen]] and water, strontium occurs naturally only in compounds with other elements, such as in the minerals [[strontianite]] and [[celestine (mineral)|celestine]]. It is kept under a liquid [[hydrocarbon]] such as [[mineral oil]] or [[kerosene]] to prevent [[oxidation]]; freshly exposed strontium metal rapidly turns a yellowish color with the formation of the oxide. Finely powdered strontium metal is [[pyrophoric]], meaning that it will ignite spontaneously in air at room temperature. Volatile strontium salts impart a bright red color to flames, and these salts are used in [[pyrotechnic]]s and in the production of [[Flare (pyrotechnic)|flares]].<ref name="CRC" /> Like calcium and barium, as well as the alkali metals and the divalent [[lanthanide]]s [[europium]] and [[ytterbium]], strontium metal dissolves directly in liquid [[ammonia]] to give a dark blue solution of solvated electrons.<ref name="Greenwood112" />

===Isotopes===
{{main|Isotopes of strontium}}

Natural strontium is a mixture of four stable [[isotope]]s: <sup>84</sup>Sr, <sup>86</sup>Sr, <sup>87</sup>Sr, and <sup>88</sup>Sr.<ref name="CRC" /> On these isotopes, <sup>88</sup>Sr is the most abundant, makes up about 82.6% of all natural strontium, though the abundance varies due to the production of [[radiogenic]] <sup>87</sup>Sr as the daughter of long-lived [[beta-decay]]ing <sup>87</sup>[[Isotopes of rubidium|Rb]].<ref>Greenwood and Earnshaw, p. 19</ref> This is the basis of [[rubidium–strontium dating]]. Of the unstable isotopes, the primary decay mode of the isotopes lighter than <sup>85</sup>Sr is [[electron capture]] or [[positron emission]] to isotopes of rubidium, and that of the isotopes heavier than <sup>88</sup>Sr is [[electron emission]] to isotopes of [[yttrium]]. Of special note are [[strontium-89|<sup>89</sup>Sr]] and [[strontium-90|<sup>90</sup>Sr]]. The former has a [[half-life]] of 50.6&nbsp;days and is used to treat [[bone cancer]] due to strontium's chemical similarity and hence ability to replace calcium.<ref name="HalperinPerez2008">{{cite book|last1=Halperin|first1=Edward C.|last2=Perez|first2=Carlos A.|last3=Brady|first3=Luther W.|title=Perez and Brady's principles and practice of radiation oncology|url=https://books.google.com/books?id=NyeE6-aKnSYC&pg=PA1997|access-date=19 July 2011|year=2008|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-6369-1|pages=1997–}}</ref><ref name="BaumanCharette2005">{{cite journal|last1=Bauman|first1=Glenn|last2=Charette|first2=Manya|last3=Reid|first3=Robert|last4=Sathya|first4=Jinka|title=Radiopharmaceuticals for the palliation of painful bone metastases – a systematic review|journal=Radiotherapy and Oncology|volume=75|issue=3|year=2005|pages=258.E1–258.E13|doi=10.1016/j.radonc.2005.03.003|pmid=16299924}}</ref> While <sup>90</sup>Sr (half-life 28.90&nbsp;years) has been used similarly, it is also an isotope of concern in [[nuclear fallout|fallout]] from [[nuclear weapons]] and [[nuclear accidents]] due to its production as a [[fission product]]. Its presence in bones can cause bone cancer, cancer of nearby tissues, and [[leukemia]].<ref name="EPA">{{cite web |url=http://www.epa.gov/rpdweb00/radionuclides/strontium.html#environment |title=Strontium {{pipe}} Radiation Protection {{pipe}} US EPA |publisher=[[United States Environmental Protection Agency|EPA]] |date=24 April 2012 |access-date=18 June 2012}}</ref> The [[Chernobyl accident|1986 Chernobyl nuclear accident]] contaminated about 30,000&nbsp;km<sup>2</sup> with greater than 10&nbsp;kBq/m<sup>2</sup> with <sup>90</sup>Sr, which accounts for about 5% of the <sup>90</sup>Sr which was in the reactor core.<ref name="OECD02-Ch1">{{cite web| url=https://www.oecd-nea.org/rp/reports/2003/nea3508-chernobyl.pdf |title=Chernobyl: Assessment of Radiological and Health Impact, 2002 update; Chapter I – The site and accident sequence |publisher=OECD-NEA | year=2002 |access-date=3 June 2015}}</ref>