http://www.ck12.org Chapter 24. Nuclear Chemistry
Lesson Summary
- Radioactive nuclides become more stable by emitting radiation in the form of small particles and energy.
- Mass defect is the difference between the mass of an atom and the sum of the masses of its particles. Upon
the formation of a nucleus, that mass is converted to energy. The nuclear binding energy released during this
process is an indicator of the stability of a nucleus. - Nuclei tend to be unstable when they are either very large or have a proton to neutron ratio that does not fall
within a band of stability. Greater stability comes from an even number of protons and/or neutrons, especially
when one or both of these values is equal to certain magic numbers. - Radioactive decay results in the formation of more stable nuclei. Types of radioactive decay include alpha
decay, beta decay, positron emission, electron capture, and gamma ray emission.
Lesson Review Questions
Reviewing Concepts
- How does an unstable nucleus release energy?
- Answer the following questions.
a. What is the relationship between mass defect and nuclear binding energy?
b. How does nuclear binding energy per nucleon relate to nuclear stability? - What changes in atomic number and mass number occur in each of the following types of radioactive decay?
a. positron emission
b. alpha decay
c. beta decay
d. electron capture - What kind of radiation is the most penetrating? The least penetrating?
Problems
- Given the following masses for isolated subatomic particles and for a neon-20 atom:
- proton = 1.00728 amu
- neutron = 1.00866 amu
- electron = 5.486× 10 −^4 amu
- neon-20 = 19.99244 amu
a. Calculate the mass defect of a neon-20 atom in amu.
b. Calculate the nuclear binding energy in J. (Use the conversion 6.0223× 1026 amu = 1 kg)
c. Calculate the nuclear binding energy per nucleon in J/nucleon.
- Calculate the neutron-proton ratio for the following nuclides. Then, use the figure above (Figure24.3) to
determine whether each nuclide is on, above, or below the band of stability.
a.^126 C
b.^137 N
c.^13450 Sn
d.^5927 Co - For each pair of nuclides listed below, indicate which one you would expect to be radioactive. Explain.