Mass

periodictable.mass

Provides average mass for the elements:

• mass, mass_units (u)

  The molar mass averaged over natural isotope abundance.

Provides mass and abundance information for isotopes:

• mass, mass_units (u)

  The molar mass of the individual isotope.

• abundance, abundance_units (%)

  Natural abundance for the isotope.

The atomic mass data for the isotopes and for the neutron were published by Wang [1] in the AME 2020 atomic mass evaluation (II).

Natural abundance mass and isotope fractions come from the IUPAC commission on isotopic abundances and atomic weights (CIAAW) [2]. This is an ill-defined problem since there is natural fractionation of the isotopes, giving different masses and ratios from different samples. The current recommended table therefore gives ranges of values for the natural mass and isotope abundance rather than a single value with an uncertainty.

For periodictable, fractionation ranges for masses were replaced with abridged standard atomic weights as given in Prohaska [3]. For the abundance ratios the center value of the range was chosen. A few elements had to be adjusted slightly so that they would sum to 100%.

The values for Ar and N were set to the values present in the atmosphere and U was set to the values in a Namibian ore per the recommendations in Meija [4].

The values for Pb in the CIAAW table are too broad to be usable. For example, 206-Pb varies from 0.02 to 0.87 in monazite samples (Zhu 2020) [5]. Rather than return NaN for composition we replace the ranges with representative atomic abundance values in Meija (2016). See the CIAAW page on lead for details.

Note: uncertainties are stored in iso._mass_unc and iso._abundance_unc, but they are not yet part of the public interface.

[1]

Meng Wang et al. (2021) Chinese Phys. C 45 030003 DOI:10.1088/1674-1137/abddaf From https://www-nds.iaea.org/amdc/ame2020/massround.mas20.txt (2023-07-06)

[2]

CIAAW. Isotopic compositions of the elements 2021. Available online at https://www.ciaaw.org.

[3]

T. Prohaska, et al. (2022) Standard atomic weights of the elements 2021. Pure Appl. Chem. 94. DOI:10.1515/pac-2019-0603 From https://www.ciaaw.org/atomic-weights.htm (2023-07-06)

[4]

J. Meija et al. (2016) Isotopic compositions of the elements 2013 Pure and Applied Chemistry 88, 293-306. From https://www.ciaaw.org/isotopic-abundances.htm (2023-07-06)

[5]

Zhu, X., Benefield, J., Coplen, T., Gao, Z. & Holden, N. (2021). Variation of lead isotopic composition and atomic weight in terrestrial materials (IUPAC Technical Report). Pure and Applied Chemistry, 93(1), 155-166. https://doi.org/10.1515/pac-2018-0916

periodictable.mass.abundance(isotope)

Natural abundance.

Parameters:

isotope : Isotope

Returns:

abundance : float | %

periodictable.mass.check_abundance(table=None)

periodictable.mass.init(table, reload=False)

Add mass attribute to period table elements and isotopes

periodictable.mass.mass(isotope)

Atomic weight.

Parameters:

isotope : Isotope

Returns:

massfloat | u

Atomic weight of the element.

periodictable.mass.print_abundance(table=None)

periodictable.mass.print_natural_mass(table=None)