Francium has isotopes so how can it's atomic mass be a whole number?

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Why do Francium, Radon, Radium, and Actinium have whole numbers for average atomic mass even though they have isotopes? But then elements like Beryllium, Fluorine, and Sodium are listed as having no isotopes but yet they have a decimal for their average atomic mass?






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    The Wikipedia data for Francium, Radon, Radium, and Actinium has mass numbers (protons + neutrons) not atomic masses since all the isotopes of these elements are radioactive.
    – MaxW
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Why do Francium, Radon, Radium, and Actinium have whole numbers for average atomic mass even though they have isotopes? But then elements like Beryllium, Fluorine, and Sodium are listed as having no isotopes but yet they have a decimal for their average atomic mass?






physical-chemistry







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M Floehr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • 1




    The Wikipedia data for Francium, Radon, Radium, and Actinium has mass numbers (protons + neutrons) not atomic masses since all the isotopes of these elements are radioactive.
    – MaxW
    51 mins ago












up vote
3
down vote

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up vote
3
down vote

favorite











Why do Francium, Radon, Radium, and Actinium have whole numbers for average atomic mass even though they have isotopes? But then elements like Beryllium, Fluorine, and Sodium are listed as having no isotopes but yet they have a decimal for their average atomic mass?






physical-chemistry







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M Floehr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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Why do Francium, Radon, Radium, and Actinium have whole numbers for average atomic mass even though they have isotopes? But then elements like Beryllium, Fluorine, and Sodium are listed as having no isotopes but yet they have a decimal for their average atomic mass?






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  • 1




    The Wikipedia data for Francium, Radon, Radium, and Actinium has mass numbers (protons + neutrons) not atomic masses since all the isotopes of these elements are radioactive.
    – MaxW
    51 mins ago












  • 1




    The Wikipedia data for Francium, Radon, Radium, and Actinium has mass numbers (protons + neutrons) not atomic masses since all the isotopes of these elements are radioactive.
    – MaxW
    51 mins ago







1




1




The Wikipedia data for Francium, Radon, Radium, and Actinium has mass numbers (protons + neutrons) not atomic masses since all the isotopes of these elements are radioactive.
– MaxW
51 mins ago




The Wikipedia data for Francium, Radon, Radium, and Actinium has mass numbers (protons + neutrons) not atomic masses since all the isotopes of these elements are radioactive.
– MaxW
51 mins ago










2 Answers
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For highly radioactive elements that don't occur in large quantities in nature, the mass number listed is the mass number of the most stable isotope. When this is done, the value is often written in brackets. The wikipedia page for the Periodic table has some nice details on the organization of the table and the values included.






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    For elements with no stable isotope (i.e. Francium, Radium, and Actinium), the atomic mass is chosen to be that of the longest lived isotope.



    Sodium has more than one isotope, so that statement is not true. But more generally, the masses for stable elements are reflective of the natural abundance of each isotope in a sample of the element.






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      For highly radioactive elements that don't occur in large quantities in nature, the mass number listed is the mass number of the most stable isotope. When this is done, the value is often written in brackets. The wikipedia page for the Periodic table has some nice details on the organization of the table and the values included.






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        up vote
        2
        down vote













        For highly radioactive elements that don't occur in large quantities in nature, the mass number listed is the mass number of the most stable isotope. When this is done, the value is often written in brackets. The wikipedia page for the Periodic table has some nice details on the organization of the table and the values included.






        share|improve this answer






















          up vote
          2
          down vote










          up vote
          2
          down vote









          For highly radioactive elements that don't occur in large quantities in nature, the mass number listed is the mass number of the most stable isotope. When this is done, the value is often written in brackets. The wikipedia page for the Periodic table has some nice details on the organization of the table and the values included.






          share|improve this answer












          For highly radioactive elements that don't occur in large quantities in nature, the mass number listed is the mass number of the most stable isotope. When this is done, the value is often written in brackets. The wikipedia page for the Periodic table has some nice details on the organization of the table and the values included.







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          answered 51 mins ago









          Tyberius

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              up vote
              2
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              For elements with no stable isotope (i.e. Francium, Radium, and Actinium), the atomic mass is chosen to be that of the longest lived isotope.



              Sodium has more than one isotope, so that statement is not true. But more generally, the masses for stable elements are reflective of the natural abundance of each isotope in a sample of the element.






              share|improve this answer
























                up vote
                2
                down vote













                For elements with no stable isotope (i.e. Francium, Radium, and Actinium), the atomic mass is chosen to be that of the longest lived isotope.



                Sodium has more than one isotope, so that statement is not true. But more generally, the masses for stable elements are reflective of the natural abundance of each isotope in a sample of the element.






                share|improve this answer






















                  up vote
                  2
                  down vote










                  up vote
                  2
                  down vote









                  For elements with no stable isotope (i.e. Francium, Radium, and Actinium), the atomic mass is chosen to be that of the longest lived isotope.



                  Sodium has more than one isotope, so that statement is not true. But more generally, the masses for stable elements are reflective of the natural abundance of each isotope in a sample of the element.






                  share|improve this answer












                  For elements with no stable isotope (i.e. Francium, Radium, and Actinium), the atomic mass is chosen to be that of the longest lived isotope.



                  Sodium has more than one isotope, so that statement is not true. But more generally, the masses for stable elements are reflective of the natural abundance of each isotope in a sample of the element.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 49 mins ago









                  PJ R

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