View source for Alkaline earth metal

{{Short description|Group of chemical elements}}
{{Distinguish|Alkali metal}}
{{Infobox periodic table group
| title       = {{nowrap|Alkaline earth metals}}
| group number= 2
| trivial name= alkaline earth metals
| by element  = beryllium group
| CAS         = IIA
| old IUPAC   = IIA
| mark        = Be,Mg,Ca,Sr,Ba,Ra
| left        = [[alkali metal]]s
| right       = [[Group 3 element|group 3]]
}}
{| class="floatright"
! colspan=2 style="text-align:left;" | ↓&nbsp;<small>[[Period (periodic table)|Period]]</small>
|-
! [[Period 2 element|2]]
| {{element cell image|4|Beryllium|Be| |Solid|Alkaline earth metal|Primordial|legend=|image=Be-140g.jpg|image caption=Lump of beryllium}}
|-
! [[Period 3 element|3]]
| {{element cell image|12|Magnesium|Mg| |Solid|Alkaline earth metal|Primordial|legend=|image=CSIRO ScienceImage 2893 Crystalised magnesium.jpg|image caption=Magnesium crystals}}
|-
! [[Period 4 element|4]]
| {{element cell image|20|Calcium|Ca| |Solid|Alkaline earth metal|Primordial|legend=|image=Calcium unter Argon Schutzgasatmosphäre.jpg|image caption=Calcium stored under argon atmosphere}}
|-
! [[Period 5 element|5]]
| {{element cell image|38|Strontium|Sr| |Solid|Alkaline earth metal|Primordial|legend=|image=Strontium destilled crystals.jpg|image caption=Strontium floating in paraffin oil}}
|-
! [[Period 6 element|6]]
| {{element cell image|56|Barium|Ba| |Solid|Alkaline earth metal|Primordial|legend=|image=Barium unter Argon Schutzgas Atmosphäre.jpg|image caption=Barium stored under argon atmosphere}}
|-
! [[Period 7 element|7]]
| {{element cell image|88|Radium|Ra| |Solid|Alkaline earth metal|from decay|legend=|image=Radium226.jpg|image caption=Radium electroplated on copper foil and covered with polyurethane to prevent reaction with air}}
|-
| colspan="2"|
----
''Legend''
{| style="text-align:center; border:0; margin:1em auto;"
|-
| style="border:{{element color|Primordial}}; background:{{Element color|table mark}};" | [[primordial element]]
|-
| style="border:{{element color|from decay}}; background:{{Element color|table mark}};padding:0 2px;" | [[radioactive decay|element by radioactive decay]]
|}
|}

The '''alkaline earth metals''' are six [[chemical element]]s in [[group (periodic table)|group]] 2 of the [[periodic table]]. They are [[beryllium]] (Be), [[magnesium]] (Mg), [[calcium]] (Ca), [[strontium]] (Sr), [[barium]] (Ba), and [[radium]] (Ra).<ref name="redbook">{{RedBook2005|pages=51}}.</ref> The elements have very similar properties: they are all shiny, silvery-white, somewhat [[reactivity (chemistry)|reactive]] [[metal]]s at [[standard temperature and pressure]].<ref name="rsc">{{cite web|url=http://www.rsc.org/chemsoc/visualelements/PAGES/data/intro_groupii_data.html |title=Visual Elements: Group 2–The Alkaline Earth Metals |author=Royal Society of Chemistry |work=Visual Elements |publisher=Royal Society of Chemistry |access-date=13 January 2012 |url-status=live |archive-url=https://web.archive.org/web/20111005182238/http://www.rsc.org/chemsoc/visualelements/pages/data/intro_groupii_data.html |archive-date=5 October 2011 |author-link=Royal Society of Chemistry }}</ref>

Together with [[helium]], these elements have in common an outer [[atomic orbital|s orbital]] which is full<ref name="rsc"/><ref>
{{cite web
 |title=Periodic Table: Atomic Properties of the Elements
 |publisher=[[National Institute of Standards and Technology]]
 |date=September 2010
 |work=nist.gov
 |url=https://www.nist.gov/pml/data/upload/periodic_table_composite_2010_nobleed.pdf
 |access-date=17 February 2012
 |url-status=live
 |archive-url=https://web.archive.org/web/20120809222201/https://www.nist.gov/pml/data/upload/periodic_table_composite_2010_nobleed.pdf
|archive-date=2012-08-09
 }}
</ref><ref name="RubberBible84th">
{{cite book
 | editor = Lide, D. R.
 | title = CRC Handbook of Chemistry and Physics
 | edition = 84th
 | location = Boca Raton, FL
 | publisher = CRC Press
 | year = 2003
}}
</ref>—that is, this orbital contains its full complement of two electrons, which the alkaline earth metals readily lose to form [[cation]]s with [[electric charge|charge]] +2, and an [[oxidation state]] of +2.<ref name="Greenwood&Earnshaw">{{Greenwood&Earnshaw2nd}}</ref> Helium is grouped with the [[noble gas]]es and not with the alkaline earth metals, but it is theorized to have some similarities to beryllium when forced into bonding and has sometimes been suggested to belong to group 2.<ref>{{cite journal |last1=Grochala |first1=Wojciech |date=1 November 2017 |title=On the position of helium and neon in the Periodic Table of Elements |journal=Foundations of Chemistry |volume=20 |pages=191–207 |issue=2018 |doi=10.1007/s10698-017-9302-7 |doi-access=free }}</ref><ref>{{cite journal |last1=Bent Weberg |first1=Libby |date=18 January 2019 |title="The" periodic table |url=https://cen.acs.org/articles/97/i3/Reactions.html |journal=Chemical & Engineering News |volume=97 |issue=3 |access-date=27 March 2020 |archive-date=1 February 2020 |archive-url=https://web.archive.org/web/20200201200009/https://cen.acs.org/articles/97/i3/Reactions.html |url-status=live }}</ref><ref>{{cite journal |last1=Grandinetti |first1=Felice |date=23 April 2013 |title=Neon behind the signs |journal=Nature Chemistry |volume=5 |issue=2013 |page=438 |doi=10.1038/nchem.1631 |pmid=23609097 |bibcode=2013NatCh...5..438G |doi-access=free }}</ref>

All the discovered alkaline earth metals occur in nature, although radium occurs only through the [[decay chain]] of [[uranium]] and [[thorium]] and not as a primordial element.<ref name="webelements-occurrence">{{cite web|url=http://www.webelements.com/webelements/properties/text/image-flash/abund-crust.html |title=Abundance in Earth's Crust |publisher=WebElements.com |access-date=14 April 2007 |url-status=live |archive-url=https://web.archive.org/web/20070309033534/http://www.webelements.com/webelements/properties/text/image-flash/abund-crust.html |archive-date=9 March 2007 }}</ref> There have been experiments, all unsuccessful, to try to synthesize [[Unbinilium|element 120]], the next potential member of the group.

== Characteristics ==

=== Chemical ===
As with other groups, the members of this family show patterns in their [[electronic configuration]], especially the outermost shells, resulting in trends in chemical behavior:

{| class="wikitable" style="white-space:nowrap;"
|-
!''[[Atomic number|Z]]'' !! [[Chemical element|Element]] !! Electrons per [[Electron shell|shell]] !! [[Electron configuration]]<ref group="n">[[Noble gas notation]] is used for conciseness; the nearest noble gas that precedes the element in question is written first, and then the electron configuration is continued from that point forward.</ref>
|-
| 4 || [[beryllium]] || 2, 2 || &#91;[[Helium|He]]&#93; 2s<sup>2</sup>
|-
| 12 || [[magnesium]] || 2, 8, 2 || &#91;[[Neon|Ne]]&#93; 3s<sup>2</sup>
|-
| 20 || [[calcium]] || 2, 8, 8, 2 || &#91;[[Argon|Ar]]&#93; 4s<sup>2</sup>
|-
| 38 || [[strontium]] || 2, 8, 18, 8, 2 || &#91;[[Krypton|Kr]]&#93; 5s<sup>2</sup>
|-
| 56 || [[barium]] || 2, 8, 18, 18, 8, 2 || &#91;[[Xenon|Xe]]&#93; 6s<sup>2</sup>
|-
| 88 || [[radium]] || 2, 8, 18, 32, 18, 8, 2 || &#91;[[Radon|Rn]]&#93; 7s<sup>2</sup>
|}

Most of the chemistry has been observed only for the first five members of the group. The chemistry of radium is not well-established due to its [[radioactive decay|radioactivity]];<ref name="rsc" /> thus, the presentation of its properties here is limited.

The alkaline earth metals are all silver-colored and soft, and have relatively low [[density|densities]], [[melting point]]s, and [[boiling point]]s. In chemical terms, all of the alkaline earth metals react with the [[halogen]]s to form the alkaline earth metal [[halide]]s, all of which are [[ionic crystal|ionic crystalline compounds]] (except for [[beryllium chloride]], [[beryllium bromide]] and [[beryllium iodide]], which are [[covalent bond|covalent]]). All the alkaline earth metals except beryllium also react with water to form strongly [[alkali]]ne [[hydroxide]]s and, thus, should be handled with great care. The heavier alkaline earth metals react more vigorously than the lighter ones.<ref name="rsc"/> The alkaline earth metals have the second-lowest first [[ionization energy|ionization energies]] in their respective periods of the [[periodic table]]<ref name="RubberBible84th"/> because of their somewhat low [[effective nuclear charge]]s and the ability to attain a [[full outer shell]] configuration by losing just two [[electron]]s. The second ionization energy of all of the alkaline metals is also somewhat low.<ref name="rsc"/><ref name="RubberBible84th" />

[[Beryllium]] is an exception: It does not react with water or steam unless at very high temperatures,<ref>{{cite web|url=http://www.chemguide.co.uk/inorganic/group2/reacth2o.html |title=Reactions of the Group 2 elements with water |last1=Clark |first1=Jim |date=December 2021 |access-date=2012-08-14 |quote='Beryllium has no reaction with water or steam even at red heat.' This was commonly quoted in textbooks....However, a researcher...sent me a photo showing the result of exposing beryllium to steam at 800°C. It definitely reacts. I think the problem is that beryllium is both expensive and carries major health risks....Textbook (or these days, web) statements about it never get checked.}}</ref> and its halides are covalent. If beryllium did form compounds with an ionization state of +2, it would polarize electron clouds that are near it very strongly and would cause extensive [[orbital overlap]], since beryllium has a high charge density. All compounds that include beryllium have a covalent bond.<ref name=deGruyter>{{cite book
 | others = trans. rev. Eagleson, Mary
 | editor1-first = Hans-Dieter | editor1-last=Jakubke
 | editor2-first = Hans | editor2-last = Jeschkeit
 | title = Concise Encyclopedia Chemistry
 | publisher = Walter de Gruyter
 | location = Berlin
 | year = 1994}}</ref> Even the compound [[beryllium fluoride]], which is the most ionic beryllium compound, has a low melting point and a low electrical conductivity when melted.<ref name="Beryllium halide and pseudohalides">{{cite book|title=Advances in inorganic chemistry and radiochemistry, Volume 14|year=1972|publisher=Academic Press|location=New York|isbn=978-0-12-023614-5|pages=256–277|chapter-url=https://books.google.com/books?id=VupzlLU9NB0C&q=beryllium+fluoride+covalent&pg=PA257|author =Bell, N. A.|editor1=Emeléus, Harry Julius |editor2=Sharpe, A. G. |chapter=Beryllium halide and pseudohalides}}</ref><ref name="Beryllium chemistry">{{cite book|last=Walsh|first=Kenneth A.|title=Beryllium chemistry and processing|publisher=ASM International|isbn=978-0-87170-721-5|pages=99–102, 118–119|url=https://books.google.com/books?id=3-GbhmSfyeYC&q=beryllium+fluoride+covalent&pg=PA119|date=2009-08-01}}</ref><ref name="General analytical chemistry of beryllium">{{cite book|title=Chemical analysis of metals: a symposium|year=1987|publisher=ASTM|isbn=978-0-8031-0942-1|pages=74–75|chapter-url=https://books.google.com/books?id=uaWTfwrG644C&q=beryllium+fluoride&pg=PA74|author =Hertz, Raymond K.|editor=Coyle, Francis T.|chapter=General analytical chemistry of beryllium}}</ref>

All the alkaline earth metals have two [[electron]]s in their valence shell, so the energetically preferred state of achieving a filled [[electron shell]] is to lose two electrons to form doubly [[electric charge|charged]] [[Positive charge|positive]] [[ion]]s.

==== Compounds and reactions ====
The alkaline earth metals all react with the [[halogens]] to form ionic halides, such as [[calcium chloride]] ({{chem|Ca|Cl|2}}), as well as reacting with [[oxygen]] to form oxides such as [[strontium oxide]] ({{chem|Sr|O}}). Calcium, strontium, and barium react with water to produce [[hydrogen gas]] and their respective [[hydroxide]]s (magnesium also reacts, but much more slowly), and also undergo [[transmetalation]] reactions to exchange [[ligand]]s.

<div style="float: left; margin: 1px; font-size:85%;">
:{| class="wikitable sortable"
|+ Solubility-related constants for alkaline-earth-metal fluorides
! Metal
! M<sup>2+</sup> hydration (-MJ/mol){{Sfn|Wiberg|Wiberg|Holleman|2001|pp=XXXVI–XXXVII}}
! "MF<sub>2</sub>" unit hydration (-MJ/mol){{sfn|Wiberg|Wiberg|Holleman|2001|p=XXXVI}}
! MF<sub>2</sub> lattice (-MJ/mol){{sfn|Lide|2004|p=12–23}}
! Solubility (mol/kL){{sfn|Wiberg|Wiberg|Holleman|2001|p=1073}}<!--originally g/L values; WP:CALC for chem use over industry-->
|-
| Be || 2.455 || 3.371 || 3.526 || soluble
|-
| Mg || 1.922 || 2.838 || 2.978 || 1.2
|-
| Ca || 1.577 || 2.493 || 2.651 || 0.2
|-
| Sr || 1.415 || 2.331 || 2.513 || 0.8
|-
| Ba || 1.361 || 2.277 || 2.373 || 6
|}
</div>
{{Clear|left}}

=== Physical and atomic ===
{| class="wikitable collapsible" style="text-align:center"
|+{{nowrap|Key physical and atomic properties}} {{nowrap|of the alkaline earth metals}}
!Alkaline earth metal
!Standard [[atomic weight]]{{br}}([[Dalton (unit)|Da]]){{refn|The number given in [[bracket|parentheses]] refers to the [[Uncertainty#In measurements|measurement uncertainty]]. This uncertainty applies to the [[significant figure|least significant figure]](s) of the number prior to the parenthesized value (i.e., counting from rightmost digit to left). For instance, {{val|1.00794|(7)}} stands for {{val|1.00794|0.00007}}, whereas {{val|1.00794|(72)}} stands for {{val|1.00794|0.00072}}.<ref>{{cite web|url=http://physics.nist.gov/cgi-bin/cuu/Info/Constants/definitions.html |title=Standard Uncertainty and Relative Standard Uncertainty |work=[[CODATA]] reference |publisher=[[National Institute of Standards and Technology]] |access-date=26 September 2011 |url-status=live |archive-url=https://web.archive.org/web/20111016021440/http://physics.nist.gov/cgi-bin/cuu/Info/Constants/definitions.html |archive-date=16 October 2011 }}</ref>|group=n}}<ref name="atomicweights2007">{{cite journal|last1=Wieser |first1=Michael E. |last2=Berglund |first2=Michael |year=2009 |title=Atomic weights of the elements 2007 (IUPAC Technical Report) |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=81 |issue=11 |pages=2131–2156 |publisher=[[International Union of Pure and Applied Chemistry|IUPAC]] |doi=10.1351/PAC-REP-09-08-03 |s2cid=98084907 |url=http://iupac.org/publications/pac/pdf/2009/pdf/8111x2131.pdf |access-date=7 February 2012 |url-status=live |archive-url=https://web.archive.org/web/20121102010700/http://iupac.org/publications/pac/pdf/2009/pdf/8111x2131.pdf |archive-date=2 November 2012 }}</ref><ref name="atomicweights2009">{{cite journal|last1=Wieser |first1=Michael E. |last2=Coplen |first2=Tyler B. |year=2011 |title=Atomic weights of the elements 2009 (IUPAC Technical Report) |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=83 |issue=2 |pages=359–396 |publisher=[[International Union of Pure and Applied Chemistry|IUPAC]] |doi=10.1351/PAC-REP-10-09-14 |s2cid=95898322 |url=http://iupac.org/publications/pac/pdf/2011/pdf/8302x0359.pdf |access-date=11 February 2012 |url-status=live |archive-url=https://web.archive.org/web/20120211145548/http://iupac.org/publications/pac/pdf/2011/pdf/8302x0359.pdf |archive-date=11 February 2012 }}</ref>
![[Melting point]]{{br}}([[kelvin|K]])
![[Melting point]]{{br}}([[Celsius|°C]])
![[Boiling point]]{{br}}([[kelvin|K]])<ref name="RubberBible84th"/>
![[Boiling point]]{{br}}([[Celsius|°C]])<ref name="RubberBible84th"/>
![[Density]]{{br}}(g/cm<sup>3</sup>)<ref name="Arblaster 2018">{{cite book |last=Arblaster |first= John W. |title=Selected Values of the Crystallographic Properties of Elements |publisher=ASM International |publication-place=Materials Park, Ohio |date=2018 |isbn=978-1-62708-155-9}}</ref>
![[Electronegativity]]{{br}}([[Pauling scale|Pauling]])
!First [[ionization energy]]{{br}}([[Kilojoule per mole|kJ·mol<sup>−1</sup>]]) !! [[Covalent radius]]{{br}}([[picometre|pm]])<ref name="slater64">{{cite journal|last=Slater|first=J. C.|year=1964|title=Atomic Radii in Crystals|journal=[[Journal of Chemical Physics]]|volume=41|issue=10|pages=3199–3205|bibcode=1964JChPh..41.3199S|doi=10.1063/1.1725697}}</ref>
! colspan="2" | [[Flame test]] color
|-
| [[Beryllium]] || 9.012182(3) || 1560 || 1287 || 2744 || 2471 || 1.845 || 1.57 || 899.5 || 105 || White<ref name="Jensen">{{cite journal|author1-link=William B. Jensen|last1=Jensen |first1=William B. |year=2003 |title=The Place of Zinc, Cadmium, and Mercury in the Periodic Table |journal=Journal of Chemical Education |volume=80 |issue=8 |pages=952–961 |publisher=[[American Chemical Society]] |doi=10.1021/ed080p952 |bibcode=2003JChEd..80..952J |url=http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/091.%20Zn-Cd-Hg.pdf |access-date=2012-05-06 |archive-url=https://web.archive.org/web/20100611152417/http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/091.%20Zn-Cd-Hg.pdf |archive-date=2010-06-11 }}</ref> ||
|-
| [[Magnesium]] || 24.3050(6) || 923 || 650 || 1363 || 1090 || 1.737 || 1.31 || 737.7 || 150 || Brilliant-white<ref name="rsc" /> ||
|-
| [[Calcium]] || 40.078(4) || 1115 || 842 || 1757 || 1484 || 1.526 || 1.00 || 589.8 || 180 || Brick-red<ref name="rsc" /> || [[File:FlammenfärbungCa.png|40px]]
|-
| [[Strontium]] || 87.62(1) || 1050 || 777 || 1655 || 1382 || 2.582 || 0.95 || 549.5 || 200 || Crimson<ref name="rsc" /> || [[File:FlammenfärbungSr.png|40px]]
|-
| [[Barium]] || 137.327(7) || 1000 || 727 || 2170 || 1897 || 3.594 || 0.89 || 502.9 || 215 || Apple-green<ref name="rsc" /> ||
|-
| [[Radium]] || [226]{{refn|The element does not have any stable [[nuclide]]s, and a value in brackets indicates the [[mass number]] of the longest-lived [[isotope]] of the element.<ref name="atomicweights2007"/><ref name="atomicweights2009"/>|group=n}} || 969 || 696 || 2010 || 1737 || 5.502 || 0.9 || 509.3 || 221 || Crimson red{{refn|The color of the flame test of pure radium has never been observed; the crimson-red color is an extrapolation from the flame test color of its compounds.<ref name="RaFlameTest">{{cite book | url = https://books.google.com/books?id=3cgQLgEACAAJ | title = The Radiochemistry of Radium | last1 = Kirby | first1 = H. W | last2 = Salutsky | first2 = Murrell L | year = 1964 | publisher = National Academies Press | bibcode = 1964nap..book21543N }}{{Dead link|date=January 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>|group=n}}
|
|}

==== Nuclear stability ====
Isotopes of all six alkaline earth metals are present in the [[Abundance of elements in Earth's crust|Earth's crust]] and the [[Solar System]] at varying concentrations, dependent upon the nuclides' half-lives and, hence, their nuclear stabilities. The first five have [[Isotopes of beryllium|one]], [[Isotopes of magnesium|three]], [[Isotopes of calcium|five]], [[Isotopes of strontium|four]], and [[Isotopes of barium|six]] stable (or observationally stable) isotopes respectively, for a total of 19 stable nuclides, as listed here: beryllium-9; magnesium-24, -25, -26; calcium-<u>40</u>, -42, -43, -44, -<u>46</u>; strontium-<u>84</u>, -86, -87, -88; barium-<u>132</u>, -134, -135, -136, -137, -138. The four underlined isotopes in the list are predicted by radionuclide decay energetics to be only observationally stable and to decay with extremely long half-lives through [[Double beta decay|double-beta decay]], though no decays attributed definitively to these isotopes have yet been observed as of 2024. Radium has no stable nor [[Primordial nuclide|primordial]] isotopes.

In addition to the stable species, calcium and barium each have one extremely long-lived and [[Primordial nuclide|primordial radionuclide]]: [[calcium-48]] and barium-130, with half-lives of {{val|5.6|e=19}} and {{val|1.6|e=21}} years, respectively. Both are far longer than the current [[age of the universe]] (4.7× and 117× billion times longer, respectively) and less than one part per ten billion has decayed since the [[formation of the Earth]]. The two isotopes are stable for practical purposes.

Apart from the 21 stable or nearly-stable isotopes, the six alkaline earth elements each possess a large number of known [[radioisotope]]s. None of the isotopes other than the aforementioned 21 are [[Primordial nuclide|primordial]]: all have half-lives too short for even a single atom to have survived since the Solar System's formation, after the seeding of heavy nuclei by nearby [[supernova]]e and [[Neutron star merger|collisions between neutron stars]], and any present are derived from ongoing natural processes. [[Beryllium-7]], [[beryllium-10]], and [[calcium-41]] are [[trace radioisotope|trace]], as well as [[Cosmogenic nuclide|cosmogenic]], nuclides, formed by the impact of [[cosmic ray]]s with atmospheric or crustal atoms. The longest half-lives among them are 1.387 million years for beryllium-10, 99.4 thousand years for calcium-41, 1599 years for [[radium-226]] (radium's longest-lived isotope), 28.90 years for [[strontium-90]], 10.51 years for barium-133, and 5.75 years for radium-228. All others have half-lives of less than half a year, most significantly shorter.

[[Calcium-48]] and barium-130, the two primordial and non-stable isotopes, decay only through [[double beta decay|double beta emission]]{{refn|Calcium-48 is theoretically capable of single [[beta decay]], but such process has never been observed.<ref name="bellidecay">{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |display-authors=3 |title=Experimental searches for rare alpha and beta decays |journal=European Physical Journal A |date=2019 |volume=55 |issue=8 |pages=140–1–140–7 |doi=10.1140/epja/i2019-12823-2 |issn=1434-601X |arxiv=1908.11458|bibcode=2019EPJA...55..140B |s2cid=201664098 }}</ref>|group=n}} and have extremely long [[half-life|half-lives]], by virtue of the extremely low probability of both beta decays occurring at the same time. All [[isotopes of radium]] are highly [[radioactivity|radioactive]] and are primarily generated through the decay of heavier radionuclides. The longest-lived of them is radium-226, a member of the [[decay chain]] of [[uranium-238]].<ref>{{Cite web |title=Uranium-235 and Uranium-238 {{!}} Hazardous Waste Cleanup Levels {{!}} Washington University in St. Louis |url=https://sites.wustl.edu/hazardouswaste/radionuclides/uranium/ |access-date=2024-01-18 |website=sites.wustl.edu}}</ref> Strontium-90 and barium-140 are common [[fission product]]s of uranium in nuclear reactors, accounting for 5.73% and 6.31% of uranium-235's fission products respectively when bombarded by thermal neutrons.<ref>{{Cite web |title=Nuclear Data for Safeguards |url=https://www-nds.iaea.org/sgnucdat/c3.htm#92-U-235 |access-date=2024-01-18 |website=www-nds.iaea.org}}</ref> The two isotopes have half-lives each of 28.90 years and 12.7 days. Strontium-90 is produced in appreciable quantities in operating nuclear reactors running on [[uranium-235]] or [[plutonium-239]] fuel, and a minuscule [[secular equilibrium]] concentration is also present due to rare [[spontaneous fission|spontaneous fission decays]] in naturally occurring uranium.

Calcium-48 is the lightest nuclide known to undergo [[double beta decay]].{{NUBASE2020|ref}} Naturally occurring calcium and barium are very weakly radioactive: calcium contains about 0.1874% calcium-48,<ref>{{cite web |url=http://ie.lbl.gov/education/parent/Ca_iso.htm |title=Isotopes of Calcium (Z=20) |author=Richard B. Firestone |date=15 March 2010 |publisher=Lawrence Berkeley National Laboratory |access-date=12 June 2012 |archive-url=https://web.archive.org/web/20120506025523/http://ie.lbl.gov/education/parent/Ca_iso.htm |archive-date=6 May 2012 }}</ref> and barium contains about 0.1062% barium-130.<ref>{{cite web |url=http://ie.lbl.gov/education/parent/Ba_iso.htm |title=Isotopes of Barium (Z=56) |author=Richard B. Firestone |date=15 March 2010 |publisher=Lawrence Berkeley National Laboratory |access-date=12 June 2012 |archive-url=https://web.archive.org/web/20120506025741/http://ie.lbl.gov/education/parent/Ba_iso.htm |archive-date=6 May 2012 }}</ref> On average, one double-beta decay of calcium-48 will occur per second for every 90 tons of natural calcium, or 230 tons of limestone (calcium carbonate).<ref>{{Cite web |title=1/(1.87e-3*1000/40.078*6.02e 23*ln2*1/(5.6e 19y/s))*1e-3*100.0869/40.078 - Wolfram{{!}}Alpha |url=https://www.wolframalpha.com/ |access-date=2024-01-18 |website=www.wolframalpha.com |language=en}}</ref> Through the same decay mechanism, one decay of barium-130 will occur per second for every 16,000 tons of natural barium, or 27,000 tons of [[baryte]] (barium sulfate).<ref>{{Cite web |title=1/(1.06e-3*1000/137.327*6.02e 23*ln2*1/(1.6e 21y/s))*1e-3*233.38/137.327 - Wolfram{{!}}Alpha |url=https://www.wolframalpha.com/ |access-date=2024-01-18 |website=www.wolframalpha.com |language=en}}</ref>

The longest-lived isotope of radium is [[radium-226]] with a half-life of 1600 years; it, along with [[radium-223]], -224, and -228, occurs naturally in the [[Decay chain#Actinide alpha decay chains|decay chain]]s of primordial [[thorium]] and [[uranium]]. [[Beryllium-8]] is notable by its absence as it splits in half virtually instantaneously into two [[alpha particle]]s whenever it is formed. The [[triple alpha process]] in stars can only occur at energies high enough for beryllium-8 to fuse with a third alpha particle before it can decay, forming [[carbon-12]]. This thermonuclear rate-limiting bottleneck is the reason most [[main sequence star]]s spend billions of years [[Hydrogen burning|fusing hydrogen]] within their cores, and only rarely manage to fuse carbon before collapsing into a stellar remnant, and even then merely for a timescale of ~1000 years.<ref>{{Cite web |title=Lecture 7: Basics of SF Stellar Nucleosynthesis |url=https://www2.mpia-hd.mpg.de/homes/semenov/Lectures/Heidelberg_Uni_2012/Lecture7_Basics_of_SF_Stellar_Nucleosynthesis.pdf |website=www2.mpia-hd.mpg.de}}</ref> The radioisotopes of alkaline earth metals tend to be "[[bone seeker]]s" as they behave chemically similar to calcium, an integral component of [[hydroxyapatite]] in compact [[bone]], and gradually accumulate in the human skeleton. The incorporated radionuclides inflict significant damage to the [[bone marrow]] over time through the emission of ionizing radiation, primarily [[alpha particle]]s. This property is made use of in a positive manner in the [[radiotherapy]] of certain [[Bone tumor|bone cancers]], since the radionuclides' chemical properties causes them to preferentially target cancerous growths in bone matter, leaving the rest of the body relatively unharmed.

Compared to their neighbors in the periodic table, alkaline earth metals tend to have a larger number of stable isotopes as they all possess an [[Even and odd atomic nuclei|even number of protons]], owing to their status as group 2 elements. Their isotopes are generally more stable due to [[Even and odd atomic nuclei|nucleon pairing]]. This stability is further enhanced if the isotope also has an even number of neutrons, as both kinds of nucleons can then participate in pairing and contribute to nuclei stability.

== History ==

=== Etymology ===

The alkaline earth metals are named after their [[oxide]]s, the ''alkaline earths'', whose old-fashioned names were [[beryllia]], [[Magnesium oxide|magnesia]], [[Calcium oxide|lime]], [[strontia]], and [[barium oxide|baria]]. These oxides are basic (alkaline) when combined with water. "Earth" was a term applied by early chemists to nonmetallic substances that are insoluble in water and resistant to heating—properties shared by these oxides. The realization that these earths were not elements but [[chemical compound|compounds]] is attributed to the chemist [[Antoine Lavoisier]]. In his ''[[Traité Élémentaire de Chimie]]'' (''Elements of Chemistry'') of 1789 he called them salt-forming earth elements. Later, he suggested that the alkaline earths might be metal oxides, but admitted that this was mere conjecture. In 1808, acting on Lavoisier's idea, [[Humphry Davy]] became the first to obtain samples of the metals by [[electrolysis]] of their molten earths,<ref name="Krebs">{{cite book| url = https://books.google.com/books?id=yb9xTj72vNAC| title = The history and use of our earth's chemical elements: a reference guide| author = Robert E. Krebs| publisher = Greenwood Publishing Group| year = 2006| isbn = 0-313-33438-2| pages=65–81}}</ref> thus supporting Lavoisier's hypothesis and causing the group to be named the ''alkaline earth metals''.

=== Discovery ===

The calcium compounds [[calcite]] and [[Lime (material)|lime]] have been known and used since prehistoric times.<ref name="minerals.usgs"/> The same is true for the beryllium compounds [[beryl]] and [[emerald]].{{sfn|Weeks|1968|p=535}} The other compounds of the alkaline earth metals were discovered starting in the early 15th century. The magnesium compound [[magnesium sulfate]] was first discovered in 1618 by a farmer at [[Epsom]] in England. Strontium carbonate was discovered in [[mineral]]s in the Scottish village of [[Strontian]] in 1790. The last element is the least abundant: radioactive [[radium]], which was extracted from [[uraninite]] in 1898.<ref name="Weeks1">{{cite journal | doi = 10.1021/ed009p1046 | title = The discovery of the elements. X. The alkaline earth metals and magnesium and cadmium|year = 1932 | last1 = Weeks | first1 = Mary Elvira |author-link1=Mary Elvira Weeks| journal = Journal of Chemical Education | volume = 9 |issue = 6 | page = 1046|bibcode = 1932JChEd...9.1046W }}</ref><ref name="Weeks2">{{cite journal | doi = 10.1021/ed009p1386 | title = The discovery of the elements. XII. Other elements isolated with the aid of potassium and sodium: Beryllium, boron, silicon, and aluminum| year = 1932 |last1 = Weeks | first1 = Mary Elvira |author-link1=Mary Elvira Weeks| journal = Journal of Chemical Education | volume = 9|issue = 8 | page = 1386|bibcode = 1932JChEd...9.1386W }}</ref><ref name="Weeks3">{{cite journal | doi = 10.1021/ed010p79 | title = The discovery of the elements. XIX. The radioactive elements | year = 1933 | last1 = Weeks | first1 = Mary Elvira |author-link1=Mary Elvira Weeks| journal = Journal of Chemical Education | volume = 10 | issue = 2 | page = 79|bibcode = 1933JChEd..10...79W }}</ref>

All elements except beryllium were isolated by electrolysis of molten compounds. Magnesium, calcium, and strontium were first produced by [[Humphry Davy]] in 1808, whereas beryllium was independently isolated by [[Friedrich Wöhler]] and [[Antoine Bussy]] in 1828 by reacting beryllium compounds with potassium. In 1910, radium was isolated as a pure metal by [[Marie Curie|Curie]] and [[André-Louis Debierne]] also by electrolysis.<ref name="Weeks1"/><ref name="Weeks2"/><ref name="Weeks3"/>

==== Beryllium ====
[[File:Béryl var. émeraude sur gangue (Muzo Mine Boyaca - Colombie) 15.jpg|thumb|right|200px|[[Emerald]] is a form of beryl, the principal mineral of beryllium.]]
[[Beryl]], a mineral that contains beryllium, has been known since the time of the [[Ptolemaic Kingdom]] in Egypt.{{sfn|Weeks|1968|p=535}} Although it was originally thought that beryl was an [[aluminium silicate|aluminum silicate]],{{sfn|Weeks|1968|p=537}} beryl was later found to contain a then-unknown element when, in 1797, [[Louis-Nicolas Vauquelin]] dissolved [[aluminium hydroxide|aluminum hydroxide]] from beryl in an alkali.<ref>{{cite journal|journal=Annales de Chimie |url=https://books.google.com/books?id=dB8AAAAAMAAJ&pg=RA1-PA155 |pages=155–169 |first=Louis-Nicolas |last=Vauquelin |title=De l'Aiguemarine, ou Béril; et découverie d'une terre nouvelle dans cette pierre |year=1798 |issue=26 |url-status=live |archive-url=https://web.archive.org/web/20160427192005/https://books.google.com/books?id=dB8AAAAAMAAJ&pg=RA1-PA155 |archive-date=2016-04-27 }}</ref> In 1828, [[Friedrich Wöhler]]<ref>{{Cite journal|journal = Annalen der Physik|volume = 89|issue = 8|pages = 577–582|title = Ueber das Beryllium und Yttrium|first = Friedrich|last = Wöhler|author-link = Friedrich Wöhler|doi = 10.1002/andp.18280890805|year = 1828|bibcode = 1828AnP....89..577W|url = https://zenodo.org/record/1423522}}</ref> and [[Antoine Bussy]]<ref>{{cite journal|journal=Journal de Chimie Médicale |url=https://books.google.com/books?id=pwUFAAAAQAAJ&pg=PA456 |pages=456–457 |first=Antoine |last=Bussy |title=D'une travail qu'il a entrepris sur le glucinium |year=1828 |issue=4 |url-status=live |archive-url=https://web.archive.org/web/20160522013803/https://books.google.com/books?id=pwUFAAAAQAAJ&pg=PA456 |archive-date=2016-05-22 }}</ref> independently isolated this new element, beryllium, by the same method, which involved a reaction of [[beryllium chloride]] with metallic [[potassium]]; this reaction was not able to produce large ingots of beryllium.{{sfn|Weeks|1968|p=539}} It was not until 1898, when [[Paul Lebeau]] performed an [[electrolysis]] of a mixture of [[beryllium fluoride]] and [[sodium fluoride]], that large pure samples of beryllium were produced.{{sfn|Weeks|1968|p=539}}

==== Magnesium ====

Magnesium was first produced by [[Humphry Davy]] in England in 1808 using electrolysis of a mixture of magnesia and [[Mercury(II) oxide|mercuric oxide]].<ref name="Davy1808">{{cite journal|last=Davy |first=H. |year=1808 |title=Electro-chemical researches on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia |journal=Philosophical Transactions of the Royal Society of London |volume=98 |pages=333–370 |bibcode=1808RSPT...98..333D |jstor=107302 |doi=10.1098/rstl.1808.0023 |url=https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 |url-status=live |archive-url=https://web.archive.org/web/20150930135639/https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 |archive-date=2015-09-30 |doi-access= |s2cid=96364168 |url-access=subscription }}</ref> [[Antoine Bussy]] prepared it in coherent form in 1831. Davy's first suggestion for a name was magnium,<ref name="Davy1808"/> but the name magnesium is now used.

==== Calcium ====

[[Lime (material)|Lime]] has been used as a material for building since 7000 to 14,000&nbsp;BCE,<ref name="minerals.usgs">{{cite web|title=Commodity report:Lime |publisher=United States Geological Survey |first=M. Michael |last=Miller |url=https://minerals.usgs.gov/minerals/pubs/commodity/lime/390498.pdf |access-date=2012-03-06 |url-status=live |archive-url=https://web.archive.org/web/20111112224558/http://minerals.usgs.gov/minerals/pubs/commodity/lime/390498.pdf |archive-date=2011-11-12 }}</ref> and [[Lime kiln|kilns used for lime]] have been dated to 2,500&nbsp;BCE in [[Khafaja]], [[Mesopotamia]].<ref>{{cite book | url =https://books.google.com/books?id=ryap1yyEGAgC&pg=PA4 | page =4 | title =Lime Kilns and Lime Burning | isbn =978-0-7478-0596-0 | last1 =Williams | first1 =Richard | year =2004 | publisher =Bloomsbury USA }}{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite book | url = https://books.google.com/books?id=vHQsGAKAdYoC| title = Lime and Limestone: Chemistry and Technology, Production and Uses | isbn = 978-3-527-61201-7 | last1 = Oates | first1 = J. A. H | date = 2008-07-01| publisher = Wiley }}</ref> Calcium as a material has been known since at least the first century, as the [[Ancient Rome|ancient Romans]] were known to have used [[calcium oxide]] by preparing it from lime. [[Calcium sulfate]] has been known to be able to set broken bones since the tenth century. Calcium itself, however, was not isolated until 1808, when [[Humphry Davy]], in [[England]], used [[electrolysis]] on a mixture of lime and [[mercuric oxide]],<ref>{{cite journal|author=Davy H |year=1808 |title=Electro-chemical researches on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia |url=https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 |journal=Philosophical Transactions of the Royal Society of London |volume=98 |pages=333–370 |bibcode=1808RSPT...98..333D |doi=10.1098/rstl.1808.0023 |url-status=live |archive-url=https://web.archive.org/web/20150930135639/https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 |archive-date=2015-09-30 |doi-access= |s2cid=96364168 |url-access=subscription }}</ref> after hearing that [[Jöns Jakob Berzelius]] had prepared a calcium amalgam from the electrolysis of lime in mercury.

==== Strontium ====

In 1790, physician [[Adair Crawford]] discovered ores with distinctive properties, which were named ''strontites'' in 1793 by [[Thomas Charles Hope]], a chemistry professor at the [[University of Glasgow]],<ref>{{cite journal |author =Murray, T.|year=1993| title= Elemementary Scots: The Discovery of Strontium |journal = Scottish Medical Journal| volume = 38 |pages = 188–189 |pmid=8146640 |issue=6|doi=10.1177/003693309303800611|s2cid=20396691}}</ref> who confirmed Crawford's discovery. Strontium was eventually isolated in 1808 by [[Humphry Davy]] by electrolysis of a mixture of [[strontium chloride]] and [[mercuric oxide]]. The discovery was announced by Davy on 30 June 1808 at a lecture to the Royal Society.<ref>{{cite book|last=Davy |first=Humphry |year=1808 |url=https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 |title=researches on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia |publisher=Philosophical Transactions of the Royal Society of London |volume=98 |pages=333–370 |url-status=live |archive-url=https://web.archive.org/web/20150930135639/https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 |archive-date=2015-09-30 }}</ref>

==== Barium ====

[[File:6158M-barite2.jpg|thumb|right|150px|Barite, the material that was first found to contain barium.]]

[[Barite]], a mineral containing barium, was first recognized as containing a new element in 1774 by [[Carl Scheele]], although he was able to isolate only [[barium oxide]]. Barium oxide was isolated again two years later by [[Johan Gottlieb Gahn]]. Later in the 18th century, [[William Withering]] noticed a heavy mineral in the [[Cumberland]] lead mines, which are now known to contain barium. Barium itself was finally isolated in 1808 when [[Humphry Davy]] used electrolysis with molten salts, and Davy named the element ''barium'', after [[baryta]]. Later, [[Robert Bunsen]] and [[Augustus Matthiessen]] isolated pure barium by electrolysis of a mixture of [[barium chloride]] and [[ammonium chloride]].<ref>{{cite journal|doi = 10.1002/jlac.18550930301|title = Masthead|year = 1855|journal = Annalen der Chemie und Pharmacie|volume = 93|issue = 3|pages = fmi|doi-access = free}}</ref><ref>{{cite journal|doi =10.1002/prac.18560670194|title =Notizen|year =1856|last1 =Wagner|first1 =Rud.|last2 =Neubauer|first2 =C.|last3 =Deville|first3 =H. Sainte-Claire|last4 =Sorel|last5 =Wagenmann|first5 =L.|last6 =Techniker|last7 =Girard|first7 =Aimé|journal =Journal für Praktische Chemie|volume =67|pages =490–508|url =https://zenodo.org/record/1427814}}</ref>

==== Radium ====

While studying [[uraninite]], on 21 December 1898, [[Marie Curie|Marie]] and [[Pierre Curie]] discovered that, even after uranium had decayed, the material created was still radioactive. The material behaved somewhat similarly to [[Compounds of barium|barium compounds]], although some properties, such as the color of the flame test and spectral lines, were much different. They announced the discovery of a new element on 26 December 1898 to the [[French Academy of Sciences]].<ref>{{cite journal|year=1898 |title=Sur une nouvelle substance fortement radio-active, contenue dans la pechblende (On a new, strongly radioactive substance contained in pitchblende) |journal=Comptes Rendus |volume=127 |pages=1215–1217 |url=http://www.aip.org/history/curie/discover.htm |access-date=2009-08-01 |author1=Curie, Pierre |author2=Curie, Marie |author3=Bémont, Gustave |url-status=live |archive-url=https://web.archive.org/web/20090806083923/http://www.aip.org/history/curie/discover.htm |archive-date=2009-08-06 }}</ref> Radium was named in 1899 from the word ''radius'', meaning ''ray'', as radium emitted power in the form of rays.<ref>{{cite encyclopedia|url=http://www.etymonline.com/index.php?term=radium |title=radium |dictionary=Online Etymology Dictionary |access-date=20 August 2011 |url-status=live |archive-url=https://web.archive.org/web/20120113061207/http://www.etymonline.com/index.php?term=radium |archive-date=13 January 2012 }}</ref>

== Occurrence ==

[[File:Erdalkali.jpg|thumb|Series of alkaline earth metals.]]

Beryllium occurs in the Earth's crust at a concentration of two to six [[parts per million]] (ppm),<ref name="Merck">{{cite book |author= |title=The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals |publisher=Merck Research Laboratories, Merck & Co., Inc. |year=2006 |isbn=0-911910-00-X |editor1-last=O'Neil |editor1-first=Marydale J. |edition=14th |location=Whitehouse Station, NJ, US |editor2-last=Heckelman |editor2-first=Patricia E. |editor3-last=Roman |editor3-first=Cherie B.}}</ref> much of which is in soils, where it has a concentration of six ppm. Beryllium is one of the rarest elements in seawater, even rarer than elements such as [[scandium]], with a concentration of 0.2 parts per trillion.<ref name="emsley">{{cite book
 | title = Nature's Building Blocks: An A–Z Guide to the Elements
 | last = Emsley
 | first = John
 | publisher = Oxford University Press
 | year = 2001
 | location = Oxford, England, UK
 | isbn = 0-19-850340-7
 | url-access = registration
 | url = https://archive.org/details/naturesbuildingb0000emsl
 }}</ref><ref>{{cite web |url=http://www.webelements.com/periodicity/abundance_seawater/ |title=Abundance in oceans |work=Mark Winter, [[The University of Sheffield]] and WebElements Ltd, UK |publisher=WebElements |access-date=6 August 2011 |archive-url=https://web.archive.org/web/20110805145627/http://www.webelements.com/periodicity/abundance_seawater/ |archive-date=5 August 2011 |df=dmy-all }}</ref> However, in freshwater, beryllium is somewhat more common, with a concentration of 0.1 parts per billion.<ref>{{cite web |url=http://www.webelements.com/periodicity/abundance_stream/ |title=Abundance in stream water |work=Mark Winter, [[The University of Sheffield]] and WebElements Ltd, UK |publisher=WebElements |access-date=6 August 2011 |archive-url=https://web.archive.org/web/20110804233559/http://www.webelements.com/periodicity/abundance_stream/ |archive-date=4 August 2011 |df=dmy-all }}</ref>

Magnesium and calcium are very common in the Earth's crust, being respectively the fifth and eighth most abundant elements. None of the alkaline earth metals are found in their elemental state.  Common magnesium-containing minerals are [[carnallite]], [[magnesite]], and [[Dolomite (mineral)|dolomite]].  Common calcium-containing minerals are [[chalk]], [[limestone]], [[gypsum]], and [[anhydrite]].<ref name="rsc"/>

Strontium is the 15th most abundant element in the Earth's crust. The principal minerals are [[celestite]] and [[strontianite]].<ref name="usgs10">{{cite web|publisher=United States Geological Survey |access-date=2010-05-14 |title=Mineral Commodity Summaries 2010: Strontium |first=Joyce A. |last=Ober |url=https://minerals.usgs.gov/minerals/pubs/commodity/strontium/mcs-2010-stron.pdf |url-status=live |archive-url=https://web.archive.org/web/20100716142558/http://minerals.usgs.gov/minerals/pubs/commodity/strontium/mcs-2010-stron.pdf |archive-date=2010-07-16 }}</ref> Barium is slightly less common, much of it in the mineral [[barite]].<ref name="ullman">{{cite book|author1=Kresse, Robert |author2=Baudis, Ulrich |author3=Jäger, Paul |author4=Riechers, H. Hermann |author5=Wagner, Heinz |author6=Winkler, Jocher |author7=Wolf, Hans Uwe |chapter=Barium and Barium Compounds|editor=Ullman, Franz|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2007|publisher=Wiley-VCH|doi=10.1002/14356007.a03_325.pub2|isbn=978-3-527-30673-2 }}</ref>

Radium, being a [[decay product]] of [[uranium]], is found in all uranium-bearing [[ore]]s.<ref name="lanl">[http://periodic.lanl.gov/88.shtml "Radium"] {{webarchive|url=https://web.archive.org/web/20121115182006/http://periodic.lanl.gov/88.shtml |date=2012-11-15 }}, Los Alamos National Laboratory. Retrieved on 2009-08-05.</ref> Due to its relatively short half-life,<ref>{{cite book|url=https://books.google.com/books?id=t-fpKQ54f44C&pg=PT115 |pages=115– |title=Radioactivity |isbn=978-0-19-983178-4 |last1=Malley |first1=Marjorie C |date=2011-08-25 |publisher=Oxford University Press, USA |url-status=live |archive-url=https://web.archive.org/web/20150905212258/https://books.google.com/books?id=t-fpKQ54f44C&pg=PT115 |archive-date=2015-09-05 }}</ref> radium from the Earth's early history has decayed, and present-day samples have all come from the much slower decay of uranium.<ref name="lanl"/>

== Production ==
[[File:Beryl-130023.jpg|thumb|upright=0.56|[[Emerald]], colored green with trace amounts of [[chromium]], is a variety of the mineral [[beryl]] which is beryllium aluminum silicate.]]Production of the six alkaline earth metals can occur in many ways.

=== Beryllium ===
{{Main article|Beryllium#Extraction}}

Most beryllium is extracted from beryllium hydroxide. One production method is [[sintering]], done by mixing [[beryl]], [[sodium fluorosilicate]], and soda at high temperatures to form sodium [[fluoroberyllate]], [[aluminium oxide|aluminum oxide]], and [[silicon dioxide]]. A solution of sodium fluoroberyllate and [[sodium hydroxide]] in [[properties of water|water]] is then used to form [[beryllium hydroxide]] by precipitation. Alternatively, in the melt method, powdered beryl is heated to high temperature, cooled with water, then heated again slightly in [[sulfuric acid]], eventually yielding beryllium hydroxide. The beryllium hydroxide from either method then produces [[beryllium fluoride]] and [[beryllium chloride]] through a somewhat long process. Electrolysis or heating of these compounds can then produce beryllium.<ref name="deGruyter" />

=== Strontium ===
{{Main article|Strontium#Production}}

In general, strontium carbonate is extracted from the mineral [[celestite]] through two methods: by leaching the celestite with [[sodium carbonate]], or in a more complicated way involving [[coal]].<ref>{{cite book|url=https://books.google.com/books?id=5smDPzkw0wEC&pg=PA401 |title=Production of SrCO, by black ash process: Determination of reductive roasting parameters |page=401 |isbn=978-90-5410-829-0 |last1=Kemal |first1=Mevlüt |last2=Arslan |first2=V |last3=Akar |first3=A |last4=Canbazoglu |first4=M |year=1996 |publisher=CRC Press |url-status=live |archive-url=https://web.archive.org/web/20160427034326/https://books.google.com/books?id=5smDPzkw0wEC&pg=PA401 |archive-date=2016-04-27 }}</ref>

=== Barium ===
{{Main article|Barium#Occurrence and production}}

To produce barium, [[Baryte|barite]] (impure barium sulfate) is converted to [[barium sulfide]] by [[carbothermic reduction]] (such as with [[Coke (fuel)|coke]]). The sulfide is water-soluble and easily reacted to form pure barium sulfate, used for commercial pigments, or other compounds, such as [[barium nitrate]]. These in turn are [[calcined]] into [[barium oxide]], which eventually yields pure barium after reduction with [[aluminium|aluminum]].<ref name="ullman" /> The most important supplier of barium is [[China]], which produces more than 50% of world supply.<ref>{{cite web|author=Miller, M. M. |url=https://minerals.usgs.gov/minerals/pubs/commodity/barite/mcs-2012-barit.pdf |title=Barite |publisher=USGS.gov |url-status=live |archive-url=https://web.archive.org/web/20120707093505/http://minerals.usgs.gov/minerals/pubs/commodity/barite/mcs-2012-barit.pdf |archive-date=2012-07-07 }}</ref>

=== Magnesium ===
{{Main article|Magnesium#Production}}

Magnesium is usually produced from [[magnesite]] ore, as well as [[dolomite (rock)|dolomite]]. When dolomite is crushed, roasted and mixed with seawater in large tanks, magnesium hydroxide settles to the bottom. Heating, mixing in coke, and reacting with chlorine, then produces molten magnesium chloride. This can be electrolyzed, releasing magnesium, which floats to the surface.<ref>{{Cite web |last=Bell |first=Terence |date=November 24, 2019 |title=How Is Magnesium Metal Produced? |url=https://www.thoughtco.com/magnesium-production-2339718#:~:text=Electrochemical%20processes%20are%20used%20to,then%20produces%20molten%20magnesium%20chloride. |access-date=23 February 2025 |website=ThoughtCo.}}</ref>

=== Calcium ===
{{Main article|Calcium#Occurrence and production}}{{Expand section|date=May 2025}}

=== Radium ===
{{Main|Radium#Production}}{{Expand section|date=May 2025}}

== Applications ==

Beryllium is used mainly in military applications,<ref>{{Cite book | last1 = Petzow | first1 = G. N. | last2 = Aldinger | first2 = F. | last3 = Jönsson | first3 = S. | last4 = Welge | first4 = P. | last5 = Van Kampen | first5 = V. | last6 = Mensing | first6 = T. | last7 = Brüning | first7 = T. | chapter = Beryllium and Beryllium Compounds | doi = 10.1002/14356007.a04_011.pub2 | title = Ullmann's Encyclopedia of Industrial Chemistry | year = 2005 | isbn = 3-527-30673-0 | s2cid = 262306041 }}</ref> but non-military uses exist. In electronics, beryllium is used as a [[p-type semiconductor|p-type]] [[dopant]] in some semiconductors,<ref>{{Cite book|url=https://archive.org/details/springer_10.1007-3-540-47852-3|page=[https://archive.org/details/springer_10.1007-3-540-47852-3/page/n117 104]|title=High-power diode lasers|author =Diehl, Roland|publisher=Springer|year=2000|isbn=3-540-66693-1}}</ref> and [[beryllium oxide]] is used as a high-strength [[electrical insulator]] and [[heat conductor]].<ref>{{Cite web|url=http://www.purdue.edu/uns/html4ever/2005/050927.Solomon.nuclear.html |date=27 September 2005 |title=Purdue engineers create safer, more efficient nuclear fuel, model its performance |publisher=Purdue University |access-date=18 September 2008 |url-status=live |archive-url=https://web.archive.org/web/20120527141643/http://www.purdue.edu/uns/html4ever/2005/050927.Solomon.nuclear.html |archive-date=27 May 2012 }}</ref> Beryllium alloys are used for mechanical parts when stiffness, light weight, and dimensional stability are required over a wide temperature range.<ref>{{Cite book|chapter-url = https://books.google.com/books?id=IpEnvBtSfPQC&pg=PA690|title = Metals handbook|chapter = Beryllium|first = Joseph R.|last = Davis|publisher = ASM International|year = 1998|isbn = 978-0-87170-654-6|pages = [https://archive.org/details/metalshandbook00davi/page/690 690–691]|url-access = registration|url = https://archive.org/details/metalshandbook00davi/page/690}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=6fdmMuj0rNEC&pg=PA62|page=62|title=Encyclopedia of materials, parts, and finishes|author =Schwartz, Mel M. |publisher=CRC Press|year=2002|isbn=1-56676-661-3}}</ref> Beryllium-9 is used in small-scale [[neutron source]]s that use the reaction {{nowrap|<sup>9</sup>Be + <sup>4</sup>He (α) → }} {{nowrap|<sup>12</sup>C + <sup>1</sup>n}}, the reaction used by [[James Chadwick]] when he [[Discovery of the neutron|discovered the neutron]]. Its low atomic weight and low neutron absorption cross-section would make beryllium suitable as a [[neutron moderator]], but its high price and the readily available alternatives such as water, [[heavy water]] and [[nuclear graphite]] have limited this to niche applications. In the [[FLiBe]] eutectic used in [[molten salt reactor]]s, beryllium's role as a moderator is more incidental than the desired property leading to its use.

Magnesium has many uses. It offers advantages over other structural materials such as [[aluminium|aluminum]], but magnesium's usage is hindered by its flammability.<ref name="Gray">{{cite book|last=Gray|first=Theodore|author-link=Theodore Gray|title=The Elements: A Visual Exploration of Every Known Atom in the Universe|year=2009|publisher=Black Dog & Leventhal Publishers|location=New York|isbn=978-1-57912-814-2|url-access=registration|url=https://archive.org/details/elementsvisualex0000gray}} {{dead link|date=March 2022}}</ref> Magnesium is often [[Magnesium alloy|alloyed]] with aluminum, zinc and manganese to increase its strength and corrosion resistance.<ref name="BakerM. M. Avedesian1999">{{cite book|last1=Baker|first1=Hugh D. R.|last2=Avedesian|first2=Michael|title=Magnesium and magnesium alloys|year=1999|publisher=Materials Information Society|location=Materials Park, OH|isbn=0-87170-657-1|page=4}}</ref> Magnesium has many other industrial applications, such as its role in the production of [[iron]] and [[steel]],{{explain | reason=what important role? | date=March 2022}} and in the [[Kroll process]] for production of [[titanium]].<ref>{{Cite book | last1 = Amundsen | first1 = K. | last2 = Aune | first2 = T. K. | last3 = Bakke | first3 = P. | last4 = Eklund | first4 = H. R. | last5 = Haagensen | first5 = J. Ö. | last6 = Nicolas | first6 = C. | last7 = Rosenkilde | first7 = C. | last8 = Van Den Bremt | first8 = S. | last9 = Wallevik | first9 = O.
| doi = 10.1002/14356007.a15_559 | chapter = Magnesium | title = Ullmann's Encyclopedia of Industrial Chemistry | year = 2003 | isbn = 3-527-30673-0 }}</ref>

Calcium is used as a [[reducing agent]] in the separation of other metals such as [[uranium]] from ore. It is  a major component of many alloys, especially [[aluminium|aluminum]] and [[copper]] alloys, and is also used to deoxidize alloys. Calcium has roles in the making of [[cheese]], [[Mortar (masonry)|mortars]], and [[cement]].<ref>{{RubberBible86th}}</ref>

Strontium and barium have fewer applications than the lighter alkaline earth metals. [[Strontium carbonate]] is used in the manufacturing of red [[firework]]s.<ref>{{cite journal | doi =10.1016/j.atmosenv.2006.09.019 | title =Recreational atmospheric pollution episodes: Inhalable metalliferous particles from firework displays | year =2007 | last1 =Moreno | first1 =Teresa | last2 =Querol | first2 =Xavier | last3 =Alastuey | first3 =Andrés | last4 =Cruz Minguillón | first4 =Mari | last5 =Pey | first5 =Jorge | last6 =Rodriguez | first6 =Sergio | last7 =Vicente Miró | first7 =José |last8 =Felis | first8 =Carles | last9 =Gibbons | first9 =Wes | journal =Atmospheric Environment | volume =41 |issue =5 | page =913|bibcode = 2007AtmEn..41..913M | hdl =10261/185836 | url =https://digital.csic.es/bitstream/10261/185836/1/Recreational%20atmospheric%20pollution%20episodes%20inhalable%20metalliferous%20particles.pdf | hdl-access =free }}</ref> Pure strontium is used in the study of [[neurotransmitter]] release in neurons.<ref>{{cite journal |doi=10.1038/2121233a0 |pmid=21090447|title=Strontium as a Substitute for Calcium in the Process of Transmitter Release at the Neuromuscular Junction |year=1966 |last=Miledi |first= R. |journal=Nature |volume=212 |issue=5067 |pages=1233–4 |bibcode = 1966Natur.212.1233M |s2cid=11109902}}</ref><ref>{{cite journal |author1=Hagler D.J., Jr |author2=Goda Y. |title= Properties of synchronous and asynchronous release during pulse train depression in cultured hippocampal neurons |journal= J. Neurophysiol. |year =2001 |volume =85|pmid=11387379 |issue=6 |pages=2324–34|doi=10.1152/jn.2001.85.6.2324 |s2cid=2907823 }}</ref> Radioactive [[strontium-90]] finds some use in [[Radioisotope thermoelectric generator|RTG]]s,<ref name="NRPA2005">{{citation |title=Assessment of environmental, health and safety consequences of decommissioning radioisotope thermal generators (RTGs) in Northwest Russia |url=http://www.nrpa.no/dav/c600d1d288.pdf |number=StrålevernRapport 2005:4 |year=2005 |publisher=[[Norwegian Radiation Protection Authority]] |location=Østerås |last1=Standring |first1=WJF |last2=Selnæs |first2=ØG |last3=Sneve |first3=M |last4=Finne |first4=IE |last5=Hosseini |first5=A |last6=Amundsen |first6=I |last7=Strand |first7=P |access-date=2019-03-13 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303210325/http://www.nrpa.no/dav/c600d1d288.pdf }}</ref><ref name=OTA94>{{cite web |title=Power Sources for Remote Arctic Applications |date=June 1994 |location=Washington, DC |publisher=U.S. Congress, Office of Technology Assessment |url=http://govinfo.library.unt.edu/ota/Ota_1/DATA/1994/9423.PDF |archive-url=https://ghostarchive.org/archive/20221009/http://govinfo.library.unt.edu/ota/Ota_1/DATA/1994/9423.PDF |archive-date=2022-10-09 |url-status=live |id=OTA-BP-ETI-129}}</ref> which utilize its [[decay heat]]. Barium is used in [[vacuum tube]]s as a [[getter]] to remove gases.<ref name="ullman"/> [[Barium sulfate]] has many uses in the [[petroleum]] industry,<ref name="RubberBible84th"/><ref>{{Cite web |title=Barium - Element information, properties and uses {{!}} Periodic Table |url=https://www.rsc.org/periodic-table/element/56/barium |access-date=2024-09-02 |website=www.rsc.org}}</ref> and other industries.<ref name="RubberBible84th"/><ref name="ullman"/><ref>{{cite book| page = [https://archive.org/details/medicinalapplica0000jone/page/102 102]| url = https://archive.org/details/medicinalapplica0000jone| url-access = registration| title= Medicinal applications of coordination chemistry|author1=Jones, Chris J.  |author2=Thornback, John | publisher =Royal Society of Chemistry| year = 2007| isbn =978-0-85404-596-9}}</ref>

Radium has many former applications based on its radioactivity, but its use is no longer common because of the adverse health effects and long half-life. Radium was frequently used in [[Radium dial|luminous paint]]s,<ref name="PMC2024184">{{cite journal|title=Radium in the healing arts and in industry: Radiation exposure in the United States|pmc=2024184|year=1954|volume=69|issue=3|pmid=13134440|last1=Terrill|first1=JG Jr.|last2=Ingraham Sc|first2=2nd|last3=Moeller|first3=DW|pages=255–62|journal=Public Health Reports|doi=10.2307/4588736|jstor=4588736}}</ref> although this use was stopped after it sickened workers.<ref>{{cite web |url=http://www.radford.edu/~wkovarik/envhist/radium.html |title=Mass Media & Environmental Conflict&nbsp;– Radium Girls |access-date=2009-08-01 |archive-url=https://web.archive.org/web/20090721113733/http://www.radford.edu/~wkovarik/envhist/radium.html |archive-date=2009-07-21 }}</ref> The [[nuclear quackery]] that alleged health benefits of radium formerly led to its addition to [[drinking water]], [[toothpaste]], and many other products.<ref name="Gray"/> Radium is no longer used even when its radioactive properties are desired because its long half-life makes safe disposal challenging. For example, in [[Brachytherapy#Radiation sources|brachytherapy]], shorter-lived alternatives such as [[iridium-192]] are usually used instead.<ref>{{cite book|url=https://books.google.com/books?id=3cT2REdXJ98C&pg=PA24 |page=24 |title=Radiation source use and replacement: Abbreviated version |isbn=978-0-309-11014-3 |last1=Committee On Radiation Source Use And Replacement |first1=National Research Council (U.S.) |last2=Nuclear And Radiation Studies Board |first2=National Research Council (U.S.) |date=January 2008 |publisher=National Academies Press |url-status=live |archive-url=https://web.archive.org/web/20150905164805/https://books.google.com/books?id=3cT2REdXJ98C&pg=PA24 |archive-date=2015-09-05 }}</ref><ref>{{cite book|url=https://books.google.com/books?id=bk0go_-FO5QC&pg=PA8 |page=8 |title=Radiation therapy planning |isbn=978-0-07-005115-7 |last1=Bentel |first1=Gunilla Carleson |year=1996 |publisher=McGraw Hill Professional |url-status=live |archive-url=https://web.archive.org/web/20150905174312/https://books.google.com/books?id=bk0go_-FO5QC&pg=PA8 |archive-date=2015-09-05 }}</ref>

==Representative reactions of alkaline earth metals==

'''''Reaction with halogens'''''
:Ca + Cl<sub>2</sub> → CaCl<sub>2</sub>
Anhydrous calcium chloride is a [[hygroscopic]] substance that is used as a desiccant. Exposed to air, it will absorb water vapour from the air, forming a solution. This property is known as [[deliquescence]].

'''''Reaction with oxygen'''''
:Ca + 1/2O<sub>2</sub> → CaO
:Mg + 1/2O<sub>2</sub> → MgO

'''''Reaction with sulfur'''''
:Ca + 1/8S<sub>8</sub> → CaS

'''''Reaction with carbon'''''

With carbon, they form acetylides 
directly. Beryllium forms carbide.

:2Be + C → Be<sub>2</sub>C
:CaO + 3C → CaC<sub>2</sub> + CO (at 2500 °C in furnace)
:CaC<sub>2</sub> + 2H<sub>2</sub>O → Ca(OH)<sub>2</sub> + C<sub>2</sub>H<sub>2</sub>
:Mg<sub>2</sub>C<sub>3</sub> + 4H<sub>2</sub>O → 2Mg(OH)<sub>2</sub> + C<sub>3</sub>H<sub>4</sub>

'''''Reaction with nitrogen'''''

Only Be and Mg form nitrides directly.
:3Be + N<sub>2</sub> → Be<sub>3</sub>N<sub>2</sub>
:3Mg + N<sub>2</sub> → Mg<sub>3</sub>N<sub>2</sub>

'''''Reaction with hydrogen'''''

Alkaline earth metals react with hydrogen to generate saline hydride that are unstable in water.
:Ca + H<sub>2</sub> → CaH<sub>2</sub>

'''''Reaction with water'''''

Ca, Sr, and Ba readily react with water to form [[hydroxide]] and [[hydrogen]] gas. Be and Mg are [[Passivation (chemistry)|passivated]] by an impervious layer of oxide. However, amalgamated magnesium will react with water vapor.
:Mg + H<sub>2</sub>O → MgO + H<sub>2</sub>

'''''Reaction with acidic oxides'''''

Alkaline earth metals reduce the nonmetal from its oxide.
:2Mg + SiO<sub>2</sub> → 2MgO + Si
:2Mg + CO<sub>2</sub> → 2MgO + C (in [[solid carbon dioxide]])

'''''Reaction with acids'''''
:Mg + 2HCl → MgCl<sub>2</sub> + H<sub>2</sub>
:Be + 2HCl → BeCl<sub>2</sub> + H<sub>2</sub>

'''''Reaction with bases'''''

Be exhibits [[Amphoterism|amphoteric]] properties. It dissolves in concentrated [[sodium hydroxide]].
:Be + NaOH + 2H<sub>2</sub>O → Na[Be(OH)<sub>3</sub>] + H<sub>2</sub>

'''''Reaction with alkyl halides'''''

Magnesium reacts with alkyl halides via an [[insertion reaction]] to generate [[Grignard reagents]].
:RX + Mg → RMgX (in anhydrous ether)

==Identification of alkaline earth cations==

'''''The flame test'''''

The table below<ref>{{Cite web |title=QUALITATIVE ANALYSIS TESTS for metal cations identifying positive ions, carbonates, ammonium ion, hydrogen ions, acids identification |url=http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc.htm |website=www.docbrown.info}}</ref> presents the colors observed when the flame of a [[Bunsen burner]] is exposed to salts of alkaline earth metals. Be and Mg do not impart colour to the flame due to their small size.<ref>{{Cite web |title=Beryllium and magnesium do not give colour to flame whereas other alkaline earth metals do so. Why? |url=https://www.askiitians.com/forums/Physical-Chemistry/beryllium-and-magnesium-do-not-give-colour-to-flam_83845.htm |website=www.askiitians.com}}</ref>

{| class="wikitable"
!'''Metal'''!!'''Colour'''
|-
|Ca||Brick-red
|-
|Sr||Crimson red
|-
|Ba||Green/Yellow
|-
|Ra||Carmine red
|}

'''''In solution'''''

'''Mg<sup>2+</sup>'''

[[Disodium phosphate]] is a very selective reagent for magnesium ions and, in the presence of ammonium salts and ammonia, forms a white precipitate of ammonium magnesium phosphate. 
:Mg<sup>2+</sup> + NH<sub>3</sub> + Na<sub>2</sub>HPO<sub>4</sub> → (NH<sub>4</sub>)MgPO<sub>4</sub> + 2Na<sup>+</sup>

'''Ca<sup>2+</sup>'''

Ca<sup>2+</sup> forms a white precipitate with ammonium oxalate. Calcium oxalate is insoluble in water, but is soluble in mineral acids.
:Ca<sup>2+</sup> + (COO)<sub>2</sub>(NH<sub>4</sub>)<sub>2</sub> → (COO)<sub>2</sub>Ca + NH<sub>4</sub><sup>+</sup>

'''Sr<sup>2+</sup>'''

Strontium ions precipitate with soluble sulfate salts.
:Sr<sup>2+</sup> + Na<sub>2</sub>SO<sub>4</sub> → SrSO<sub>4</sub> + 2Na<sup>+</sup>

All ions of alkaline earth metals form white precipitate with ammonium carbonate in the presence of ammonium chloride and ammonia.

==Compounds of alkaline earth metals==

'''''Oxides'''''

The alkaline earth metal oxides are formed from the thermal decomposition of the corresponding [[carbonates]].
:CaCO<sub>3</sub> → CaO + CO<sub>2</sub> (at approx. 900°C)
In laboratory, they are obtained from hydroxides:
:Mg(OH)<sub>2</sub> → MgO + H<sub>2</sub>O
or nitrates:
:Ca(NO<sub>3</sub>)<sub>2</sub> → CaO + 2NO<sub>2</sub> + 1/2O<sub>2</sub>
The oxides exhibit basic character: they turn [[phenolphthalein]] red and [[litmus]], blue. They react with water to form hydroxides in an exothermic reaction.
:CaO + H<sub>2</sub>O → Ca(OH)<sub>2</sub> + Q
Calcium oxide reacts with carbon to form acetylide.
:CaO + 3C → CaC<sub>2</sub> + CO (at 2500°C)
:CaC<sub>2</sub> + N<sub>2</sub> → CaCN<sub>2</sub> + C
:CaCN<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → CaSO<sub>4</sub> + H<sub>2</sub>N—CN
:H<sub>2</sub>N—CN + H<sub>2</sub>O → (H<sub>2</sub>N)<sub>2</sub>CO ([[urea]])
:CaCN<sub>2</sub> + 2H<sub>2</sub>O → CaCO<sub>3</sub> + NH<sub>3</sub>

'''''Hydroxides'''''

They are generated from the corresponding oxides on reaction with water. They exhibit basic character: they turn [[phenolphthalein]] pink and [[litmus]], blue. Beryllium hydroxide is an exception as it exhibits [[Amphoterism|amphoteric]] character.
:Be(OH)<sub>2</sub> + 2HCl → BeCl<sub>2</sub> + 2 H<sub>2</sub>O
:Be(OH)<sub>2</sub> + NaOH → Na[Be(OH)<sub>3</sub>]

'''''Salts'''''

Ca and Mg are found in nature in many compounds such as [[Dolomite (mineral)|dolomite]], [[aragonite]], [[magnesite]] (carbonate rocks). Calcium and magnesium ions are found in [[hard water]]. Hard water represents a multifold issue. It is of great interest to remove these ions, thus softening the water. This procedure can be done using reagents such as [[calcium hydroxide]], [[sodium carbonate]] or [[sodium phosphate]]. A more common method is to use ion-exchange [[aluminosilicate]]s or [[ion-exchange resins]] that trap Ca<sup>2+</sup> and Mg<sup>2+</sup> and liberate Na<sup>+</sup> instead:
:Na<sub>2</sub>O·Al<sub>2</sub>O<sub>3</sub>·6SiO<sub>2</sub> + Ca<sup>2+</sup> → CaO·Al<sub>2</sub>O<sub>3</sub>·6SiO<sub>2</sub> + 2Na<sup>+</sup>

== Biological role and precautions ==
{{expand section|date=January 2013}}

Magnesium and calcium are ubiquitous and essential to all known living organisms. They are involved in more than one role, with, for example, magnesium or calcium [[ion transporter|ion pumps]] playing a role in some cellular processes, magnesium functioning as the active center in some [[enzymes]], and calcium salts taking a structural role, most notably in bones.

Strontium plays an important role in marine aquatic life, especially hard corals, which use strontium to build their [[exoskeleton]]s. It and barium have some uses in medicine, for example "[[barium meal]]s" in radiographic imaging, whilst strontium compounds are employed in some [[toothpaste]]s. Excessive amounts of [[strontium-90]] are toxic due to its radioactivity and strontium-90 mimics calcium (i.e. Behaves as a "[[bone seeker]]") where it [[bioaccumulation|bio-accumulates]] with a significant [[biological half life]]. While the bones themselves have higher radiation tolerance than other tissues, the rapidly dividing [[bone marrow]] does not and can thus be significantly harmed by Sr-90. The effect of [[ionizing radiation]] on bone marrow is also the reason why [[acute radiation syndrome]] can have [[anemia]]-like symptoms and why donation of [[red blood cell]]s can increase survivability.

Beryllium and radium, however, are toxic. Beryllium's low aqueous solubility means it is rarely available to biological systems; it has no known role in living organisms and, when encountered by them, is usually highly toxic.<ref name=deGruyter/> Radium has a low availability and is highly radioactive, making it toxic to life.

== Extensions ==

The next alkaline earth metal after radium is thought to be [[Unbinilium|element 120]], although this may not be true due to [[relativistic quantum chemistry|relativistic effects]].<ref name="tanm">{{cite web|url=http://lch.web.psi.ch/files/lectures/TexasA&M/TexasA&M.pdf |title=Gas Phase Chemistry of Superheavy Elements |author=Gäggeler, Heinz W. |date=5–7 November 2007 |work=Lecture Course Texas A&M |access-date=26 February 2012 |archive-url=https://web.archive.org/web/20120220090755/http://lch.web.psi.ch/files/lectures/TexasA%26M/TexasA%26M.pdf |archive-date=20 February 2012 }}</ref> The synthesis of element 120 was first attempted in March 2007, when a team at the [[Flerov Laboratory of Nuclear Reactions]] in [[Dubna]] bombarded [[plutonium]]-244 with [[iron]]-58 ions; however, no atoms were produced, leading to a limit of 400 [[barn (unit)|fb]] for the cross-section at the energy studied.<ref>{{cite journal|journal=Phys. Rev. C|volume=79|article-number=024603|year=2009|title=Attempt to produce element 120 in the <sup>244</sup>Pu+<sup>58</sup>Fe reaction|doi=10.1103/PhysRevC.79.024603|last1=Oganessian|first1=Yu. Ts.|last2=Utyonkov|first2=V.|last3=Lobanov|first3=Yu.|last4=Abdullin|first4=F.|last5=Polyakov|first5=A.|last6=Sagaidak|first6=R.|last7=Shirokovsky|first7=I.|last8=Tsyganov|first8=Yu.|last9=Voinov|first9=A.|issue=2|bibcode = 2009PhRvC..79b4603O }}</ref> In April 2007, a team at the [[Gesellschaft für Schwerionenforschung|GSI]] attempted to create element 120 by bombarding [[uranium]]-238 with [[nickel]]-64, although no atoms were detected, leading to a limit of 1.6 pb for the reaction. Synthesis was again attempted at higher sensitivities, although no atoms were detected. Other reactions have been tried, although all have been met with failure.<ref name="Duellmann">{{Cite web |title=Home / FIAS |url=https://fias.institute/ |access-date=2024-02-11 |website=fias.institute}}</ref>

The chemistry of element 120 is predicted to be closer to that of [[calcium]] or [[strontium]]<ref name=EB/> instead of [[barium]] or [[radium]]. This noticeably contrasts with [[periodic trends]], which would predict element 120 to be more reactive than barium and radium. This lowered [[reactivity (chemistry)|reactivity]] is due to the expected energies of element 120's valence electrons, increasing element 120's [[ionization energy]] and decreasing the [[metallic radius|metallic]] and [[ionic radius|ionic radii]].<ref name=EB>{{cite encyclopedia|author=Seaborg, G. T. |url=https://www.britannica.com/EBchecked/topic/603220/transuranium-element |title=transuranium element (chemical element) |encyclopedia=Encyclopædia Britannica |date=c. 2006 |access-date=16 March 2010 |url-status=live |archive-url=https://web.archive.org/web/20101130112151/https://www.britannica.com/EBchecked/topic/603220/transuranium-element |archive-date=30 November 2010 }}</ref>

The next alkaline earth metal after element 120 has not been definitely predicted. Although a simple extrapolation using the [[Aufbau principle]] would suggest that element 170 is a congener of 120, [[relativistic quantum chemistry|relativistic effects]] may render such an extrapolation invalid. The next element with properties similar to the alkaline earth metals has been predicted to be element 166, though due to overlapping orbitals and lower energy gap below the 9s subshell, element 166 may instead be placed in [[group 12 element|group 12]], below [[copernicium]].<ref name="Fricke">{{cite journal |last1=Fricke |first1=B. |last2=Greiner |first2=W. |last3=Waber |first3=J. T. |year=1971 |title=The continuation of the periodic table up to Z = 172. The chemistry of superheavy elements |journal=Theoretica Chimica Acta |volume=21 |issue=3 |pages=235–260 |doi=10.1007/BF01172015|s2cid=117157377 }}</ref><ref name=Haire>{{cite book| title=The Chemistry of the Actinide and Transactinide Elements| editor1-last=Morss|editor2-first=Norman M.| editor2-last=Edelstein| editor3-last=Fuger|editor3-first=Jean| last1=Hoffman|first1=Darleane C. |last2=Lee |first2=Diana M. |last3=Pershina |first3=Valeria |chapter=Transactinides and the future elements| publisher= [[Springer Science+Business Media]]| year=2006| isbn=978-1-4020-3555-5| location=Dordrecht, The Netherlands| edition=3rd| ref=CITEREFHaire2006}}</ref>

== See also ==
* [[Alkaline earth octacarbonyl complex]]es

== Explanatory notes ==
{{reflist|group="n"}}

== References ==
{{reflist|30em}}

== Bibliography ==
*{{cite book |last=Lide |first=David R. |title=Handbook of Chemistry and Physics|url=https://archive.org/details/crchandbookofche81lide |url-access=registration |publisher=CRC Press|year=2004|edition=84th|isbn=978-0-8493-0566-5 }}
* {{cite book
 | last1 = Weeks
 | first1 = Mary Elvira
 | author-link=Mary Elvira Weeks
 | last2= Leichester|first2=Henry M.
 | year = 1968
 | title = Discovery of the Elements
 | url = https://archive.org/details/discoveryofeleme0000week
 | url-access = registration
 | publisher = Journal of Chemical Education
 | location = Easton, PA
 | id = LCCCN 68-15217
 | ref = CITEREFWeeks1968
 }}
*{{cite book|last1=Wiberg |first1= Egon |last2= Wiberg |first2=Nils |last3=Holleman |first3=Arnold Frederick|title=Inorganic chemistry|url=https://books.google.com/books?id=Mtth5g59dEIC|access-date=3 March 2011|year=2001|publisher=Academic Press|isbn=978-0-12-352651-9}}

==Further reading==
* [http://www.rsc.org/chemsoc/visualelements/pages/data/intro_groupii_data.html Group 2 – Alkaline Earth Metals], Royal Chemistry Society.
* Hogan, C. Michael. 2010. [https://web.archive.org/web/20120612123626/http://www.eoearth.org/article/Calcium?topic=49557 "Calcium"]. A. Jorgensen, C. Cleveland, eds. ''Encyclopedia of Earth''. National Council for Science and the Environment.
* Maguire, Michael E. "Alkaline Earth Metals". ''Chemistry: Foundations and Applications''. Ed. [[J. J. Lagowski]]. Vol. 1. New York: Macmillan Reference USA, 2004. 33–34. 4 vols. Gale Virtual Reference Library. Thomson Gale.
* Petrucci R.H., Harwood W.S., and Herring F.G., General Chemistry (8th edition, Prentice-Hall, 2002)
* Silberberg, M.S., ''Chemistry: The Molecular Nature of Matter and Change'' (3rd edition, McGraw-Hill, 2009)

{{Alkaline earth metals}}
{{Periodic table (navbox)}}
{{Navbox periodic table}}
{{Authority control}}

[[Category:Alkaline earth metals| ]]
[[Category:Groups (periodic table)]]
[[Category:Periodic table]]