

A007656


Mass number of the most abundant isotope of the element with atomic number Z = n.
(Formerly M3296)


7



1, 4, 7, 9, 11, 12, 14, 16, 19, 20, 23, 24, 27, 28, 31, 32, 35, 40, 39, 40, 45, 48, 51, 52, 55, 56, 59, 58, 63, 64, 69, 74, 75, 80, 79, 84, 85, 88, 89, 90, 93, 98, 98, 102, 103, 106, 107, 114, 115, 120, 121, 130, 127, 132, 133, 138, 139, 140, 141, 142, 145, 152, 153, 158, 159, 164, 165, 168, 169, 174, 175, 180, 181, 184, 187, 192, 193, 195, 197, 202, 205, 208, 209, 209, 210, 222, 223, 226, 227, 232, 231, 238, 237, 244, 243, 247, 247, 251, 252, 257, 258, 259, 262, 261, 262, 266, 264, 277, 268, 281, 272, 285, 289
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OFFSET

1,2


COMMENTS

Mass number of the most abundant of the stable nuclides with atomic number equal to n. If there is no stable isotope, choose the one with the longest decay time.
Sequence is not welldefined, since the entries may change as more properties of the elements are discovered.
Moss and Winter give the atomic weight for Dysprosium (Dy) as "162.50(3)"; rounded to 163 rather than 162.
Bentor, Winter and Moss all give 145 as the atomic weight of the most stable isotope of Promethium (Pm), as opposed to 147, which was in the original data (between 144 and 150).
The largestnumbered element in the sequence is now element 114, Ununquadium (Uuq), with an atomic weight of 289 for the most stable isotope.
Also referred to as the mass number A of the most abundant and stable nuclide with atomic number Z=n. We have A = Z + N, where N is the neutron number A058317(n).  Lekraj Beedassy, Oct 08 2005
The 'abundance' refers to the Earth's crust. It may differ when applied to other astronomical bodies and/or to the known Universe. The mass numbers (once also referred to as the isotope numbers) are always integer, and should not be confused with relative atomic masses (or isotope masses), nor with (mean) atomic weights, none of which are ever integer.  Stanislav Sykora, Apr 26 2015


REFERENCES

W. M. Haynes, Editor, CRC Handbook of Chemistry and Physics, CRC Press 2014, 95th Edition. See section Nuclear and Particle Physics, chapter Table of the Isotopes.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=1..113.
Y. Bentor, Chemical Elements.Com
R. B. Firestone & L. P. Ekstrom, Table of Radioactive Isotopes
G. P. Moss, Atomic Weights of the Elements 1999
M. E. Wieser, T. B. Coplen, Atomic weights of the elements 2009 (IUPAC Technical Report), Pure Appl. Chem., 83 (2010), 359396, DOI:10.1351/PACREP100914.
M. Winter, WebElements Periodic Table
Wikipedia, Atomic number
Wikipedia, Atomic mass
Wikipedia, Mass number


EXAMPLE

Calcium (Ca), with atomic number 20, has 6 stable isotopes with mass numbers 40, 42, 43, 44, 46, and 48. Of these, 40Ca is the most abundant in Earth's crust (96.941%). Hence a(20)=40. Note: The relative atomic mass of 40Ca is 39.96259..., smaller than 40 because of the mass equivalent of the nuclear bonding energy, while the conventional mean atomic weight of Calcium is presently 40.078(4), by IUPAC 2009.  Stanislav Sykora, Apr 26 2015


MATHEMATICA

Needs["Miscellaneous`ChemicalElements`"]; Table[ Round[ AtomicWeight[ Elements[[n]]]], {n, 1, 105}] (* above element 105, the values differ *)


CROSSREFS

Cf. A058317, A121818, A179301.
Sequence in context: A272015 A273916 A053169 * A159619 A272454 A207017
Adjacent sequences: A007653 A007654 A007655 * A007657 A007658 A007659


KEYWORD

nonn,fini,changed


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from AndrĂ© Engels
Further terms from Philip Newton, Oct 26 2001, using data from Moss
Comments from David Terr: There are several errors in this sequence. It looks to me that the rounded atomic weights were used rather than the mass number of the most abundant of the stable nuclides with atomic number equal to n. Thus for instance, a(28) should be 58, not 59 and a(29) should be 63, not 64. In fact, in all cases the parity of a(n) should be the same as n (both odd or both even).  David Terr, Oct 05 2006
I fixed all the entries I could find in which a(n) was incorrect, based on the online table of isotopic abundances at http://www.sisweb.com/referenc/source/exactmas.htm.  David Terr, Apr 06 2009
a(n) has the same parity as n for all stable elements except beryllium (n=4, a(n)=9), nitrogen (n=7, a(n)=14) and platinum (n=78, a(n)=195).  David Terr, Apr 07 2009
Name clarified by Stanislav Sykora and Jon E. Schoenfield, May 04 2015


STATUS

approved



