III. Atomic Structures

III-III. Calculations of atomic mass

1. The three stable isotopes of silicon have masses and natural abundances as follows. Calculate the atomic mass.

   28Si	27.976927 amu	92.23%
   29Si	28.976495 amu	4.67%
   30Si	29.973770 amu	3.10%
2. There are two stable isotopes of bromine. Isotope A has a mass of 78.918336 amu and isotope B has a mass of 80.916289 amu.
   
   • Determine the natural abundance of the isotopes, and report the answer to three significant figures.
     
     
   • Write the symbol for the two isotopes.
3. There are two naturally occurring isotopes of silver, ^107AgAg and ¹⁰⁹Ag. The atomic mass of silver is 107.87 amu, with 51.82% of the atoms being ¹⁰⁷Ag. The mass of an atom of ¹⁰⁷Ag is 106.9 amu. What is the mass, in amu, of an atom of ¹⁰⁹Ag.
   
   
   

   Rosamaría Fong, Instructor of Chemistry,
   British Columbia Institute of Technology, Burnaby, B.C. Canada.

   

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   Rosamaría Fong, Instructor of Chemistry
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