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Question

Argon atoms have a mass number of 40, but a relative atomic mass of 39.948 why is this so?


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Solution

Argon:

  • Argon is an element with an atomic symbol Ar and an atomic number 20.
  • The mass number of Argon is 40.

Relative atomic mass:

  • The stable isotopes of Argon are (36Ar,38Ar,and40Ar).
  • The abundance of 36Ar is 0.334%.
  • The abundance of 37Ar is 0.0629%.
  • The abundance of 40Ar is 99.604%.
  • The average atomic mass of the element argon will be given as:

Averageatomicmass=i(isotopei×abundancei)

  • Averageatomicmass=35.96755u×0.003336+37.96273u×0.000629+39.96238u×0.996035Averageatomicmass=39.948u

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