AP Physics Essentials Video 3: The Atomic Nucleus

Introduction

• Presenter: Mr. Anderson
• Topic: Atomic Nucleus
• Key Scientist: Ernest Rutherford

Historical Background

• JJ Thompson: Discovered the electron (negative charge).
• Plum Pudding Model: Early model of the atom with electrons (negative charges) interspersed in a positive "pudding."

Rutherford's Experiment

• Method: Shot alpha particles (positive charge) at atoms.
• Observation: Most particles passed through, but some were deflected or bounced back.
• Conclusion: Existence of a dense, positively charged nucleus.

Composition of the Nucleus

• Protons: Positive charge, determine the element.
  • Example: 6 protons = carbon; 1 proton = hydrogen.
• Neutrons: No charge, vary in number among isotopes.

Isotopes

• Definition: Atoms of the same element with different numbers of neutrons.
• Examples:
  • Carbon-12: 6 protons, 6 neutrons.
  • Carbon-14: 6 protons, 8 neutrons.
• Radioactivity: Some isotopes are unstable and decay, releasing radiation.

Periodic Table

• Atomic Number: Number of protons determines the element.
  • Hydrogen = 1 proton
  • Iron = 26 protons
  • Gold = 79 protons
• Naturally Occurring Isotopes: Vary in neutron number, e.g., Uranium
  • Uranium-238: 146 neutrons
  • Uranium-235: 143 neutrons
  • Uranium-234: 142 neutrons

Stability and Decay

• Graph Explanation: Number of protons vs. neutrons.
• Stability: Larger nuclei require more neutrons for stability.
• Types of Radiation:
  • Alpha particles: 2 protons and 2 neutrons.
  • Beta particles: Electrons or positrons.
  • Gamma radiation: High-energy electromagnetic radiation.

Radioactive Decay

• Example: Uranium-238 decaying to Thorium through alpha decay.
• Half-Life: Time taken for half of a sample to decay.
  • Uranium-238 half-life: 4.5 billion years.

Application of Half-Life

• Dating Samples: Determine age of rocks through remaining Uranium-238.

Conclusion

• Nucleus Structure: Protons and neutrons determine properties and stability.
• Isotopes: Can be stable or unstable, leading to decay and radiation emission.

---

• End Note: Understanding the atomic nucleus helps explain the fundamental properties and behaviors of elements.