UNIT # 3 Introduction Objectives 3.1 Structure of the Atom 3.2 3.3 Arrangement of Electrons 3.4 3.5 Atomic Mass Problems 1 | 2 | 3

Unit # 3 - Atomic Structure
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, 107Ag 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.

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