Understanding Atomic Theory

Introduction to Atomic Theory

• Visualization of atoms has evolved significantly over centuries.
• Greek Philosophers (Leucippus & Democritus)
  • Proposed matter is composed of tiny, indivisible particles called "atomos."
  • Believed properties of substances were due to the form of their particles.

Evolution of Atomic Theory

• Antoine Lavoisier
  • Proposed the law of conservation of mass: matter's mass remains constant despite shape or form changes.
• James Dalton
  • Stated elements exist as discrete packets of matter.
• 19th Century Developments
  • Introduction of discharge tubes leading to the identification of cathode rays.

Discoveries in Atomic Structure

• Cathode Rays
  • 1860s-1870s: Cathode rays identified as negatively charged.
  • Eugen Goldstein
    • Discovered positive charge in matter using discharge tubes.
  • J.J. Thompson
    • Determined cathode rays were actually negatively-charged particles (electrons).
    • Proposed the "plum pudding model" of the atom where electrons are scattered in a positively charged matrix.

Advances in Atomic Models

• Ernest Rutherford
  • 1909: Gold foil experiment led to discovery of the nucleus – a small, dense, positively charged center.
  • Identified protons as fundamental particles within the nucleus.
• Niels Bohr
  • Developed the planetary model of the atom with electrons in orbits around the nucleus.
  • Linked electron positions to energy levels and orbitals.

Quantum Theory of the Atom

• Werner Heisenberg
  • Introduced the Heisenberg Uncertainty Principle: Impossibility of knowing both an electron’s position and momentum with certainty.
  • Proposed a quantum theory that considers electrons as probability clouds, not defined orbits.
  • Introduced the concept of orbitals where electrons are likely to be found.

Conclusion

• Current understanding is a collective effort from various scientists over centuries.
• Quantum model is the latest but continues to be refined.
• Encouragement for ongoing inquiry and experimentation in chemistry and physics.

Miscellaneous

• This lecture is part of a series provided by Crash Course Chemistry.
• Credits to writers, editors, chemistry consultants, and the production team.