Editing Alkali metal (section)

== Occurrence ==

=== In the Solar System ===
[[File:SolarSystemAbundances.svg|thumb|upright=2.5|Estimated abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the [[Big Bang]]. The next three elements (lithium, [[beryllium]], and [[boron]]) are rare because they are poorly synthesised in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. Iron is especially common because it represents the minimum-energy nuclide that can be made by fusion of helium in supernovae.<ref name=lodders>{{cite journal |last1= Lodders |first1= Katharina|author1-link=Katharina Lodders |year= 2003 |title= Solar System Abundances and Condensation Temperatures of the Elements |journal= The Astrophysical Journal |volume= 591 |issue= 2 |pages= 1220–1247 |bibcode= 2003ApJ...591.1220L |doi= 10.1086/375492|doi-access= free }}</ref>]]
The [[Oddo–Harkins rule]] holds that elements with even atomic numbers are more common that those with odd atomic numbers, with the exception of hydrogen. This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability.<ref name=oddo>{{cite journal |doi= 10.1002/zaac.19140870118 |title= Die Molekularstruktur der radioaktiven Atome |year= 1914 |last1= Oddo |first1= Giuseppe |journal= Zeitschrift für Anorganische Chemie |volume= 87 |pages= 253–268 |url= https://www.academia.edu/11043300 |archive-date= 25 July 2020 |access-date= 16 November 2016 |archive-url= https://web.archive.org/web/20200725145835/https://www.academia.edu/11043300/Die_Molekularstruktur_der_radioaktiven_Atome |url-status= live }}</ref><ref name=harkins>{{cite journal |doi= 10.1021/ja02250a002 |year= 1917 |last1= Harkins |first1= William D. |journal= Journal of the American Chemical Society |volume= 39 |issue= 5 |pages= 856–879 |title= The Evolution of the Elements and the Stability of Complex Atoms. I. A New Periodic System Which Shows a Relation Between the Abundance of the Elements and the Structure of the Nuclei of Atoms |bibcode= 1917JAChS..39..856H |url= https://zenodo.org/record/1429060 |archive-date= 22 September 2020 |access-date= 28 June 2019 |archive-url= https://web.archive.org/web/20200922024136/https://zenodo.org/record/1429060 |url-status= live }}</ref><ref name=north>{{cite book |last=North|first=John|title=Cosmos an illustrated history of astronomy and cosmology|year=2008|publisher=Univ. of Chicago Press|isbn=978-0-226-59441-5|page=602|url=https://books.google.com/books?id=qq8Luhs7rTUC&q=%22william+draper+harkins%22+oddo&pg=PA602|edition=Rev. and updated}}</ref> All the alkali metals have odd atomic numbers and they are not as common as the elements with even atomic numbers adjacent to them (the [[noble gas]]es and the [[alkaline earth metal]]s) in the Solar System. The heavier alkali metals are also less abundant than the lighter ones as the alkali metals from rubidium onward can only be synthesised in [[supernova]]e and not in [[stellar nucleosynthesis]]. Lithium is also much less abundant than sodium and potassium as it is poorly synthesised in both [[Big Bang nucleosynthesis]] and in stars: the Big Bang could only produce trace quantities of lithium, [[beryllium]] and [[boron]] due to the absence of a stable nucleus with 5 or 8 [[nucleon]]s, and stellar nucleosynthesis could only pass this bottleneck by the [[triple-alpha process]], fusing three helium nuclei to form [[carbon]], and skipping over those three elements.<ref name=lodders />

=== On Earth ===
[[File:Spodumene-usa59abg.jpg|thumb|upright|[[Spodumene]], an important lithium mineral]]
The Earth formed from the same cloud of matter that formed the Sun, but the planets acquired different compositions during the [[formation and evolution of the Solar System]]. In turn, the [[history of Earth|natural history of the Earth]] caused parts of this planet to have differing concentrations of the elements. The mass of the Earth is approximately 5.98{{e|24}}&nbsp;kg. It is composed mostly of iron (32.1%), [[oxygen]] (30.1%), [[silicon]] (15.1%), [[magnesium]] (13.9%), [[sulfur]] (2.9%), [[nickel]] (1.8%), [[calcium]] (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to [[planetary differentiation]], the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.<ref name=pnas71_12_6973>{{cite journal |last1=Morgan|first1=J. W. |last2=Anders|first2=E. |title=Chemical composition of Earth, Venus, and Mercury |journal=Proceedings of the National Academy of Sciences |year=1980 |volume=77 |issue=12 |pages=6973–6977 |doi=10.1073/pnas.77.12.6973 |pmid=16592930 |pmc=350422 |bibcode= 1980PNAS...77.6973M|doi-access=free }}</ref>

The alkali metals, due to their high reactivity, do not occur naturally in pure form in nature. They are [[Goldschmidt classification|lithophiles]] and therefore remain close to the Earth's surface because they combine readily with [[oxygen]] and so associate strongly with [[silica]], forming relatively low-density minerals that do not sink down into the Earth's core. Potassium, rubidium and caesium are also [[incompatible element]]s due to their large [[ionic radii]].<ref name="albarede">{{cite book |title= Geochemistry: an introduction |url= https://books.google.com/books?id=doVGzreGq14C&pg=PA17 |publisher= Cambridge University Press |year= 2003 |isbn= 978-0-521-89148-6 |first= Francis |last= Albarède}}</ref>

Sodium and potassium are very abundant on Earth, both being among the ten [[abundance of elements in Earth's crust|most common elements in Earth's crust]];<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|archive-date= 9 March 2007|archive-url= https://web.archive.org/web/20070309033534/http://www.webelements.com/webelements/properties/text/image-flash/abund-crust.html|url-status= live}}</ref><ref name="IsraelScience&Technology">{{cite web|url= https://www.science.co.il/elements/?s=Earth|title= List of Periodic Table Elements Sorted by Abundance in Earth's crust|publisher= Israel Science and Technology Directory|access-date= 5 July 2021|archive-date= 2 February 2017|archive-url= https://web.archive.org/web/20170202002014/http://www.science.co.il/elements/?s=Earth|url-status= live}}</ref> sodium makes up approximately 2.6% of the Earth's crust measured by weight, making it the [[Abundance of the chemical elements|sixth most abundant element]] overall<ref name="RubberBible86th">{{RubberBible86th}}</ref> and the most abundant alkali metal. Potassium makes up approximately 1.5% of the Earth's crust and is the seventh most abundant element.<ref name="RubberBible86th" /> Sodium is found in many different minerals, of which the most common is ordinary salt (sodium chloride), which occurs in vast quantities dissolved in seawater. Other solid deposits include [[halite]], [[amphibole]], [[cryolite]], [[nitratine]], and [[zeolite]].<ref name="RubberBible86th" /> Many of these solid deposits occur as a result of ancient seas evaporating, which still occurs now in places such as [[Utah]]'s [[Great Salt Lake]] and the [[Dead Sea]].<ref name="Greenwood&Earnshaw" />{{rp|69}} Despite their near-equal abundance in Earth's crust, sodium is far more common than potassium in the ocean, both because potassium's larger size makes its salts less soluble, and because potassium is bound by silicates in soil and what potassium leaches is absorbed far more readily by plant life than sodium.<ref name="Greenwood&Earnshaw" />{{rp|69}}

Despite its chemical similarity, lithium typically does not occur together with sodium or potassium due to its smaller size.<ref name="Greenwood&Earnshaw" />{{rp|69}} Due to its relatively low reactivity, it can be found in seawater in large amounts; it is estimated that lithium concentration in seawater is approximately 0.14 to 0.25 parts per million (ppm)<ref>{{cite web |url=http://www.ioes.saga-u.ac.jp/ioes-study/li/lithium/occurence.html |title=Lithium Occurrence |access-date=13 March 2009 |publisher=Institute of Ocean Energy, Saga University, Japan |url-status=dead |archive-url=https://web.archive.org/web/20090502142924/http://www.ioes.saga-u.ac.jp/ioes-study/li/lithium/occurence.html |archive-date=2 May 2009}}</ref><ref name=enc>{{cite web|url=http://www.enclabs.com/lithium.html|access-date=15 October 2010|title=Some Facts about Lithium|publisher=ENC Labs|archive-date=10 July 2011|archive-url=https://web.archive.org/web/20110710191644/http://www.enclabs.com/lithium.html|url-status=dead}}</ref> or 25 [[micromolar]].<ref>{{cite book |doi=10.1007/3-540-13534-0_3|chapter=Extraction of metals from sea water|volume= 124/1984|pages= 91–133|last=Schwochau|first=Klaus|year=1984|series=Topics in Current Chemistry|isbn=978-3-540-13534-0|title=Inorganic Chemistry|s2cid=93866412 }}</ref> Its diagonal relationship with magnesium often allows it to replace magnesium in [[ferromagnesium]] minerals, where its crustal concentration is about 18&nbsp;[[parts per million|ppm]], comparable to that of [[gallium]] and [[niobium]]. Commercially, the most important lithium mineral is [[spodumene]], which occurs in large deposits worldwide.<ref name="Greenwood&Earnshaw" />{{rp|69}}

Rubidium is approximately as abundant as [[zinc]] and more abundant than copper. It occurs naturally in the minerals [[leucite]], [[pollucite]], [[carnallite]], [[zinnwaldite]], and [[lepidolite]],<ref>{{cite journal |title= Trace element chemistry of lithium-rich micas from rare-element granitic pegmatites |volume= 55
|issue= 13 |year= 1995 |doi= 10.1007/BF01162588 |pages= 203–215 |journal= Mineralogy and Petrology |first= M. A. |last= Wise |bibcode= 1995MinPe..55..203W|s2cid= 140585007
}}</ref> although none of these contain only rubidium and no other alkali metals.<ref name="Greenwood&Earnshaw" />{{rp|70}} Caesium is more abundant than some commonly known elements, such as [[antimony]], [[cadmium]], [[tin]], and [[tungsten]], but is much less abundant than rubidium.<ref name="pubs.usgs" />

[[Francium-223]], the only naturally occurring isotope of francium,<ref name="atomicweights2007" /><ref name="atomicweights2009" /> is the [[decay product|product]] of the [[alpha decay]] of actinium-227 and can be found in trace amounts in [[uranium]] minerals.<ref name="CRC2006">{{cite book |year= 2006 |title= CRC Handbook of Chemistry and Physics |volume= 4|page= 12|publisher= CRC|isbn= 978-0-8493-0474-3}}</ref> In a given sample of uranium, there is estimated to be only one francium atom for every 10<sup>18</sup> uranium atoms.<ref name="nbb">{{cite book |last= Emsley|url=https://books.google.com/books?id=Yhi5X7OwuGkC&pg=PA151 |first= John |title= Nature's Building Blocks |publisher= Oxford University Press |year= 2001 |location= Oxford |pages= 151–153 |isbn= 978-0-19-850341-5}}</ref><ref name="elemental">{{cite web |last= Gagnon |first= Steve |title= Francium |publisher= Jefferson Science Associates, LLC |url= http://education.jlab.org/itselemental/ele087.html |access-date= 1 April 2007 |archive-url= https://web.archive.org/web/20070331235139/http://education.jlab.org/itselemental/ele087.html |archive-date= 31 March 2007  |url-status= live}}</ref> It has been calculated that there are at most 30&nbsp;grams of francium in the [[crust (geology)|earth's crust]] at any time, due to its extremely short [[half-life]] of 22 minutes.<ref name="Winter" /><ref name="itselemental">{{cite web |url= http://education.jlab.org/itselemental/index.html|title= It's Elemental&nbsp;— The Periodic Table of Elements|publisher= Jefferson Lab|access-date= 14 April 2007 |archive-url= https://web.archive.org/web/20070429032414/http://education.jlab.org/itselemental/index.html |archive-date= 29 April 2007  |url-status= live}}</ref>