Lecture: History of Atomic Theory

Introduction

Atomic Theory: Understanding chemistry involves understanding the history and acceptance of atomic theory.
Atoms: Fundamental particles that make up all matter.

Democritus: First proposed the concept of indivisible particles called "atomos".
- Philosophy rather than science initially.

Empirical Evidence: Dalton provided the first evidence supporting the existence of atoms.
Atomic Theory:
- Compounds consist of different types of atoms in whole number ratios.
- Chemical reactions involve rearrangement of these atoms.
Example: Water composition by mass (1/9 hydrogen, 8/9 oxygen).
- Explained by identical water molecules with a consistent number of hydrogen and oxygen atoms.
Element Combination: Explained how elements combine to form different compounds (e.g., carbon and oxygen).

JJ Thomson: Discovered the electron, indicating that atoms consist of smaller particles.
- Cathode Ray Experiment: Demonstrated particles with negative charge ejected from neutral material.
- Plum Pudding Model: Proposed model without clear distribution of charges.

Ernest Rutherford: Conducted the gold foil experiment.
- Experiment Details:
  - Fired positively charged alpha particles at thin gold foil.
  - Most particles passed through; some scattered at high energy.
- Conclusion: Positive charges are condensed in the nucleus.
- Atomic Structure: Electrons are far from the nucleus, making the atom mostly empty space.
- Significance: Explained the scattering of alpha particles.

Atomic Model Development: Confirmed the existence of atoms and illuminated aspects of their structure.
Impact on Chemistry: Understanding atomic structure allowed chemistry to progress and flourish.