History of the Atom

Introduction

• Overview of the evolution of atomic theory.
• Key scientists and their contributions to the understanding of atomic structure.

Early Atomic Theory

Democritus (c. 500 BC)

• Proposed the idea of atomic theory.
• Concept: Everything is composed of tiny, indivisible particles (atoms) separated by empty space.

19th Century Developments

John Dalton (1800s)

• Described atoms as solid spheres.
• Introduced the idea that different elements consist of different types of atoms.

J.J. Thomson (1897)

• Developed the "plum pudding model."
• Discovered negatively charged particles (electrons) within atoms.
• Proposed atoms as balls of positive charge with embedded electrons.

Early 20th Century Discoveries

Ernst Rutherford (1909)

• Conducted gold foil experiment with alpha particles.
• Disproved the "plum pudding model" by observing deflections.
• Proposed the nuclear model with a central nucleus containing positive charge.

Flaw in Rutherford's Model

• Lack of explanation for electron cloud stability around the nucleus, suggesting atoms would collapse.

Niels Bohr (1913)

• Proposed that electrons orbit the nucleus like planets around the sun.
• Introduced the concept of electron shells.
• This model prevented the collapse of the atom and laid the foundation for modern atomic theory.

Further Developments

Innovations by Rutherford

• Discovered that the nucleus is made of protons.

James Chadwick

• Provided evidence for neutrons within the nucleus.

Conclusion

• The Bohr model forms the basis of our current understanding of atomic structure with minor updates.
• Continued experimentation has refined our knowledge of atomic particles and structure.