SCH3U Isotope Exercise
1. What are the names, symbols, electrical charges, and masses (expressed in
amu) of the three subatomic particles?
2. Where is nearly all of the mass of an atom located? Explain your answer in
terms of what contributes to this mass.
3. Define the terms atomic number and mass number.
4. How are isotopes of the same element alike? How do they differ?
5. The composition of ordinary neon is: neon-20, 90.92 %; neon-21, 0.26 %;
neon-22, 8.82 %. Calculate the average atomic mass of neon.
6. Natural lithium comes in only two isotopes of Li-6 (7.42%) and Li-7 (92.58%).
Determine the average atomic mass for Lithium.
7. Boron occurs as two natural isotopes of B-10 (19.78%) and B-11 (80.22%).
Determine the average atomic mass for boron.
8. Calculate the relative atomic mass of gallium given that the relative
abundance of its two isotopes are: 60.5% of Ga-69 and 39.5% of Ga-71
9. Oxygen occurs as one major isotope and two minor isotopes. O-16 (99.759%) ,
O-17 (0.037%) and O-18 (0.204%). Calculate the average atomic mass of
oxygen.
10. Iron has four isotopes; Fe-54 (5.82%); Fe-56 (91.66%); Fe-57 (2.19%) and Fe58 (0.33%). Determine the average atomic mass for natural iron.
11. Nickel has five naturally occurring isotopes. We will exclude all the special
isotopes synthetically made in nuclear reactors. The isotopes are:
Ni-58 67.88% Ni-60 26.23% Ni-61 1.19% Ni-62 3.66% Ni-64 1.08%
Calculate the average atomic mass of nickel.
12. Iridium (a metal rather like platinum) occurs with only two isotopes of mass
number 191 and 193. The atomic weight of iridium is 192.2. Deduce the
relative abundance of the two isotopes of this element.
13. A recently discovered element has been given the symbol RU (recently
unknown). It has an average atomic mass of 255.84 amu. There are only two
isotopes of RU, these being RU-253 and RU-259. Determine the relative
percentages of these two isotopes.
14. Natural Rb consists solely of the isotopes Rb-85 and Rb-87. From the atomic
mass of Rb (85.4678) calculate the relative percentages of these two isotopes.
15. There are only two naturally occurring isotopes of strettonium (St). There are
St-335 and St-338. (The first person to make a joke about Strettonium being a
heavy element will be summarily flogged.) St-335 makes up 69.00% of all
know Strettonium. Determine the average atomic mass of Strettonium.