Editing Alkali metal (section)

=== 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 />