Aren’t the atomic weights of the elements constants of nature?
Some of the atomic weight can be considered in the same category as constants of nature. For example, the standard atomic weight of fluorine in the 2005 Commission report is 18.998 4032(5). The uncertainty is 2.6 × 10–8. Compare this to uncertainties of 5 × 10–8 for the Avogadro constant, 1.7 × 10–6 for the Boltzmann constant, and 5 × 10–8 for the Planck constant (See http://physics.nist.gov/cuu/Constants/index.html). The atomic weight of an element is equal to the sum of the products of the fraction of each isotope of the element and the atomic mass of the respective isotope, which typically is known with an uncertainty of 1 x 10–8. In the case of fluorine and other monoisotopic elements, which comprise only a single isotope, the atomic weights of these elements are known with low uncertainties because the respective atomic masses are known with high accuracy. However, the majority of chemical elements are polyisotopic and their atomic weights are limited by the uncertainty with which
Some of the atomic weights can be considered in the same category as constants of nature. For example, the standard atomic weight of fluorine in the 2005 Commission report is 18.998 4032(5). The uncertainty is 2.6 × 10–8. Compare this to uncertainties of 5 × 10–8 for the Avogadro constant, 1.7 × 10–6 for the Boltzmann constant, and 5 × 10–8 for the Planck constant (See http://physics.nist.gov/cuu/Constants/index.html). The atomic weight of an element is equal to the sum of the products of the fraction of each isotope of the element and the atomic mass of the respective isotope, which typically is known with an uncertainty of 1 x 10–8. In the case of fluorine and other elements with one stable isotope, the atomic weights of these elements are known with low uncertainties because the respective atomic masses are known with high accuracy. However, the majority of chemical elements have two or more stable isotopes and their atomic weights are limited by the uncertainty with which the fract
