History of the Atom

Introduction

• Overview of the development of atomic theory.
• Focus on key scientists and their contributions to understanding atomic structure.

Atomic Theory

• Democritus (c. 500 BC)
  • Proposed the concept that everything is made up of tiny, indivisible particles called atoms.
  • Suggested atoms are separated by empty space.

19th Century Developments

• John Dalton (1800s)
  • Described atoms as solid spheres.
  • Suggested different elements are made from different types of spheres (atoms).

Discovery of Electrons

• J.J. Thompson (1897)
  • Developed the "plum pudding model."
  • Proposed atoms consist of a ball of positive charge with negatively charged electrons within.

Rutherford's Nuclear Model

• Ernest Rutherford (1909)
  • Conducted experiments firing alpha particles at gold foil.
  • Observed deflections inconsistent with the "plum pudding model."
  • Suggested a nuclear model with a compact nucleus containing positive charge.
  • Proposed that electrons exist in a cloud around the nucleus.

Bohr's Planetary Model

• Niels Bohr (1913)
  • Proposed electrons orbit the nucleus similar to planets orbiting the sun.
  • Introduced the concept of electron shells to prevent collapse of atom.
  • Model supported by many subsequent experiments and remains largely valid today.

Further Discoveries

• Further Contributions by Rutherford
  • Identified positive charge in nucleus as discrete particles (protons).
• James Chadwick
  • Provided evidence for neutrons, neutral particles in the nucleus.

Conclusion

• Current understanding of atomic structure largely based on these historical models.
• These developments provided a framework for modern atomic theory.