Nuclear Chemistry Concepts and Principles

Nuclear Forces and Stability

• The atomic nucleus contains positively charged protons, leading to electromagnetic repulsion between them.
• The strong nuclear force holds the nucleus together, overcoming the electromagnetic repulsion, which is crucial for the stability of larger atoms.
• This strong nuclear force is responsible for the immense energy released during nuclear reactions, such as fission, which is fundamental to nuclear power and weapons.

Band of Stability

• Understanding the band of stability is essential; it relates to the ratio of neutrons to protons in a nucleus.
• Stable isotopes are shown in graphs as purple dots; generally, stable nuclei exist for elements with atomic numbers below 80.
• For elements above calcium (atomic number 20), more neutrons than protons are needed for stability due to increased electromagnetic repulsion among protons.
• The stable ratio can shift; for instance, as the atomic number increases, the required neutron to proton ratio also increases:
  • Near atomic number 37, the ratio is approximately 1:2 (neutrons:protons).
  • At around atomic number 80, the ratio is about 1.5:1.
• Elements above atomic number 83 are radioactive and unstable. This instability arises because the neutron to proton ratio cannot maintain balance.

Decay Processes

• Neutron to proton ratio decides the type of decay a nucleus undergoes.
• If a nucleus has too many neutrons, it may experience beta decay, converting a neutron into a proton and thus becoming more stable.
• Nuclei with atomic numbers greater than 83 typically undergo alpha emission, losing two protons and two neutrons to achieve stability.

Conservation of Mass in Nuclear Reactions

• Unlike chemical reactions, mass is not conserved in nuclear reactions; some mass is converted to energy according to Einstein's equation $E=mc^2$.
• This conversion highlights that in nuclear decay processes, a small amount of mass results in a significant energy release.

Half-Life

• The half-life ($t_{1/2}$) is the time required for half of the radioactive nuclei in a sample to decay.
• For instance, if you start with a 100% sample:
  • After one half-life, 50% remains;
  • After two half-lives, 25%;
  • After three half-lives, 12.5%.
• Half-lives can vary greatly:
  • Carbon-14: $5,730$ years;
  • Uranium-238: $4.5$ billion years;
  • Radon-222: $3.8$ days.

Conclusion

• Understanding the balance between neutrons and protons is critical in comprehending stability, decay, and the energetic nature of nuclear chemistry.