Question
Tue July 10, 2012 By:
 

how to calculate atomic mass of an element?

Expert Reply
Tue July 10, 2012
An atomic weight (relative atomic mass) of an element from a specified source is the ratio of the average mass per atom of the element to 1/12 of the mass of 12C" 

Atomic Mass =

[(%abundance of isotope) (mass of isotope)] + [(%abundance of isotope) (mass of isotope)] + [….]    

Ex: The natural abundance for boron isotopes is: 19.9% 10B (10.013 amu) and 80.1% 11B (11.009amu). Calculate the atomic weight of boron. 

Atomic Mass = [(0.199)(10.013)] + [(0.801)(11.009)]
 = [1.992587] + [8.818209]
= 10.810796 so, the atomic weight of B = 10.811

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