Atomic Mass Atomic mass

					Atomic #, Mass #, Atomic mass

1. Complete the following table for each isotope.

                Isotope      Atomic      Mass
                                                    Protons     Neutrons Electrons
                Symbol       Number     Number
Molybdenum-       96
                       Mo      42          96          42           54           42
     96           42

                   ?Ag                                              61

                               14                                   14

                                           39                       20

                                                       26           30

                               50          110

                   118   I

2. One way in which the Earth’s evolution as a planet can be understood is by
measuring the amounts of certain nuclides in rocks. One quantity recently
measured is the ratio of 129Xe to 130Xe in some minerals. In what way do these two
nuclides differ from one another, and in in what respects are they the same? (An
atom of a specific isotope is called a nuclide.)

3. a) What isotope is used as the standard in establishing the atomic mass scale?

b) The atomic weight of chlorine is reported as 35.5, yet no atom of chlorine has the
mass of
35.5 amu. Explain.

4. Silicon occurs in nature as a mixture of three isotopes: 28Si (27.98 amu), 29Si
(28.98 amu), and 30Si (29.97 amu). The mixture is 92.21% 28Si, 4.70% 29Si, and
3.09% 30Si. Calculate the atomic mass of naturally occurring silicon.

5. The atomic mass of the element gallium is 69.72 amu. If it is composed of two
isotopes, 69Ga (68.926 amu) and 71Ga (70.925 amu), what is the percent of 69Ga?
6. a) γ rays are not deflected by an electric field. What can we conclude about γ
radiation from this observation?

b) Why are α and β rays deflected in opposite directions by an electric field?

Adapted from Chemistry: The Central Science by Brown, LeMay, and Bursten and Basic Concepts of Chemistry by
Leo J. Malone.