Accelerated Chemistry: Democritus, Dalton, & Other Atomic Dead Guys

Overview of Atomic Theory Development

Key Scientists and Their Contributions

Democritus (400 B.C.)

• Proposed everything is made up of indivisible particles termed "atoms".

Aristotle (330 B.C.)

• Introduced the concept of four elements: air, earth, fire, and water.

John Dalton (1766-1844)

• Formulated atomic theory based on experimental evidence.

• Defined atoms as indivisible particles.

• Suggested that atoms of the same element are identical.

• Proposed that atoms of different elements can combine in fixed ratios.

J.J. Thomson (1856-1940)

• Discovered the electron using cathode ray experiments.

• Developed the Plum Pudding Model of atomic structure.

Ernest Rutherford (1871-1937)

• Conducted the Gold Foil Experiment, revealing the existence of a nucleus.

Eugen Goldstein (1850-1930)

• Discovered protons through the investigation of cathode rays.

James Chadwick (1891-1974)

• Discovered neutrons, completing the understanding of atomic structure.

Summary of Atomic Structure

• Atoms consist of three subatomic particles:

  • Electrons (negative charge)

  • Protons (positive charge) located in the nucleus

  • Neutrons (neutral charge) also in the nucleus