Lecture Notes: Chapter 26 - Understanding Atomic Structure

Introduction

• Focus on atomic scale understanding.
• Relates to chemistry concepts for understanding atomic structures.

Rutherford’s Alpha Scattering Experiment

• Setup:
  • Circular fluorescent screen used.
  • Source of alpha particles, e.g., Americium-241.
  • Alpha particles: Positively charged, helium nuclei (4/2 He).
• Procedure:
  • Alpha particles shot at a thin gold foil.
  • Observes particle deflection on the screen.

Observations from the Experiment

1. Undeflected Particles:
   • Most particles pass through undeflected.
   • Conclusion: Atoms are mostly empty space.
2. Slightly Deflected Particles:
   • Some particles deflect slightly.
   • Conclusion: Deflection due to positively charged nucleus repelling alpha particles.
3. Large Angle Deflection:
   • Some particles deflect at large angles or bounce back.
   • Conclusion: Collisions with dense, positively charged nucleus.

Rutherford's Atomic Model Conclusions

• Atom mostly empty space.
• Dense, positively charged nucleus at center.
• Nucleus contains protons (positive) and neutrons (neutral).
• Electrons orbit the nucleus.

Atomic Structure

• Protons:
  • Mass: 1u = 1.66 x 10^-27 kg.
  • Charge: +1e (1.6 x 10^-19 coulombs).
• Neutrons:
  • Mass: Similar to protons, 1u.
  • Charge: Neutral (0 charge).
• Electrons:
  • Mass: Much smaller than protons (9.1 x 10^-31 kg).
  • Charge: -1e (-1.6 x 10^-19 coulombs).

Nuclear Terminologies

• Nucleon Number (A): Total protons + neutrons in nucleus.
• Proton Number (Z): Number of protons, defines the element.
• Isotopes:
  • Same proton number, different neutron number.
  • Example: Carbon isotopes (C-12, C-13, C-14).

Summary

• Understanding nucleus and atomic structure provides insight into chemistry and physics.
• Next topic: Nuclear reactions in upcoming videos.

These notes cover the fundamental concepts related to the atomic structure and the historical Rutherford experiment that shaped modern understanding of atomic physics.