Nuclear Chemistry and Radioactivity

Overview

• Introduction to Nuclear Chemistry
  • Combined with chemical kinetics and atomic structure
• Two parts of Nuclear Chemistry:
  1. Theoretical part
     • Definitions: Radioactivity, radioactive disintegration series, stability of the nucleus
     • Related to atomic structure
  2. Numerical part
     • First order kinetics of radioactive decay
     • Applications: Rock dating, carbon dating

Lecture Structure

• 3-4 initial lectures for 11th class students after atomic structure
• 2-3 later lectures after chemical kinetics

Key Concepts

Nuclear Chemistry

• Nucleus as a 'black box'; primarily studied in physics
• Research focused on understanding the nucleus: nucleons (neutrons and protons) distribution
• Extranuclear chemistry vs. intranuclear chemistry

Radioactivity

• Definition:
  • Spontaneous decay of unstable nuclei without external excitation
  • Emission of alpha, beta, and gamma rays
• Unstable nuclei undergo nuclear decay spontaneously

Nuclear Stability

• Stability of the nucleus:
  • Electronic repulsion reduced by the spread of electrons in large space
  • Nuclear forces: Operate at nuclear distances (around 10^-15 meters or femtometer)
  • Nuclear forces of attraction are stronger than electrostatic repulsion among protons
  • Evidence from alpha particle scattering experiment

Potential Energy vs Distance

• Potential energy increases with distance due to columbic repulsion
• At nuclear distances, attractive nuclear forces dominate
  • Attractive forces among protons and neutrons create stability

Yukawa's Meson Theory

• Proposed in 1935 by Yukawa for nucleus stability
• Rapid exchange of pi mesons between nucleons (protons and neutrons) leads to stability
  • Pi mesons: electrically neutral, positive, or negative
  • Heavier than electrons

Mass Defect and Binding Energy

• Mass defect: Atoms are slightly lighter than the sum of their constituent particles
  • Example: Oxygen-16 atom has mass 15.99 amu vs. sum of 16.13 amu
• Binding energy: Energy released when forming a nucleus from its nucleons
  • Calculated using Einstein's equation: E = ΔM * c²
  • 1 amu mass loss corresponds to approximately 931.4 MeV energy released
• Higher binding energy per nucleon = greater stability of the nucleus
  • Maximum binding energy per nucleon around mass number 60 (Iron)

Fusion and Fission

• Light nuclei undergo fusion for stability
• Heavy nuclei undergo fission to reach stable zones
  • Example: Fusion in stars, like the sun

Conclusion

• Overview of nuclear stability, mass defect, and binding energy
• Future discussions on magic numbers and related topics in next lectures