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Tuesday, August 29, 2023

Average Atomic Mass/weight or Relative Atomic Mass:

Elements are found in different isotopic forms (atoms of same elements having different atomic mass), so the atomic mass of any element is the average of all the isotopic mass within a given sample. 


(A) If an elements exists in two isotopes having atomic masses ‘M1’ and ‘M2 in the ratio   X: Y, then

or

(B) If an elements exists in two isotopes having atomic masses ‘M1’ and ‘M2  and their abundant  percentage (%)  are  X % and Y % then

Since the atomic mass is a ratio, it has no units and is expressed in amu.

Illustrative Examples:

(1) Calculate the average atomic mass of silicon if relative abundance is 92.23 ,isotope Si^28, 4.77 % isotope = Si^29 and 3% isotope = Si^39 .






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