Atomic Mass Of Elements


The relative atomic mass of an element is the weighted average of the masses of the isotopes on a scale on which a carbon-12 atom has a mass of exactly 12 units. A 'weighted average' allows for the fact that there won't be equal amounts of the various isotopes. The example coming up should make that clear. This table lists the mass and percent natural abundance for the stable nuclides. The mass of the longest lived isotope is given for elements without a stable nuclide. Nuclides marked with an asterisk (.) in the abundance column indicate that it is not present in nature or that a meaningful natural abundance cannot be given. Sega saturn homebrew. The isotopic mass.

Version History and References Disclaimer

  1. History of the atomic mass unit Stanislao Cannizzaro (1826–1910), the pioneer in this field, adopted the hydrogen atom as a standard of mass and set its atomic weight at 2. Others accepted the idea of using a specific atom as a standard of.
  2. Chemical elements listed by atomic mass The elements of the periodic table sorted by atomic mass. Click on any element's name for further information on chemical properties, environmental data or health effects. This list contains the 118 elements of chemistry.

Developers and Contributors:

J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset
NIST Physical Measurement Laboratory


The atomic weights are available for elements 1 through 118 and isotopic compositions or abundances are given when appropriate. The atomic weights data were published by J. Meija et al in Atomic Weights of the Elements 2013, and the isotopic compositions data were published by M. Berglund and M.E. Wieser in Isotopic Compositions of the Elements 2009. The relative atomic masses of the isotopes data were published by M. Wang, G. Audi, A.H. Wapstra, F.G. Kondev, M. MacCormick, X. Xu1, and B. Pfeiffer in The AME2012 Atomic Mass Evaluation.


These data have been compiled from the above sources for the user's convenience and does not represent a critical evaluation by the NIST Physical Measurement Laboratory.


Related Links

Atomic mass of elements 1 to 20 rounded off

Atomic Mass Of Elements Pdf

Development of this database was funded in part by NIST's Systems Integration for Manufacturing Applications (SIMA) Program.
Online: September 1999 Last update: January 2015