magic number (chemistry)

{{Short description|Number of atoms present in the clusters of critical sizes with higher stability}}

{{More references|date=January 2024}}

The concept of magic numbers in the field of chemistry refers to a specific property (such as stability) for only certain representatives among a distribution of structures. It was first recognized by inspecting the intensity of mass-spectrometric signals of rare gas cluster ions.{{cite journal |doi=10.1103/PhysRevLett.51.1538 |title=Experimental Investigation of Small Helium Clusters: Magic Numbers and the Onset of Condensation |date=1983 |last1=Stephens |first1=Peter W. |last2=King |first2=John G. |journal=Physical Review Letters |volume=51 |issue=17 |pages=1538–1541 |bibcode=1983PhRvL..51.1538S }} Then, the same effect was observed with sodium clusters.{{cite journal |doi=10.1103/PhysRevLett.52.2141 |title=Electronic Shell Structure and Abundances of Sodium Clusters |date=1984 |last1=Knight |first1=W. D. |last2=Clemenger |first2=Keith |last3=De Heer |first3=Walt A. |last4=Saunders |first4=Winston A. |last5=Chou |first5=M. Y. |last6=Cohen |first6=Marvin L. |journal=Physical Review Letters |volume=52 |issue=24 |pages=2141–2143 |bibcode=1984PhRvL..52.2141K }}{{cite journal |doi=10.1038/scientificamerican1297-50 |title=Metal Clusters and Magic Numbers |date=1997 |last1=Brack |first1=Matthias |journal=Scientific American |volume=277 |issue=6 |pages=50–55 |bibcode=1997SciAm.277f..50B }}

In case a gas condenses into clusters of atoms, the number of atoms in these clusters that are most likely to form varies between a few and hundreds. However, there are peaks at specific cluster sizes, deviating from a pure statistical distribution. Therefore, it was concluded that clusters of these specific numbers of atoms dominate due to their exceptional stability. The concept was also successfully applied to explain the mono-dispersed occurrence of thiolate-protected gold clusters; here the outstanding stability of specific cluster sizes is connected with their respective electronic configuration.

The term magic numbers is also used in the field of nuclear physics. In this context, magic numbers refer to a specific number of protons or neutrons that forms complete nucleon shells.{{Cite web |title=The Complete Explanation of the Nuclear Magic Numbers Which Indicate the Filling of Nucleonic Shells and the Revelation of Special Numbers Indicating the Filling of Subshells Within Those Shells |url=https://www.sjsu.edu/faculty/watkins/magicnumbers2.htm |access-date=2024-03-25 |website=www.sjsu.edu}}