Atomic Theory Timeline Flashcards

Ancient Philosophical Foundations

• Democritus (460-370 BC) proposed the concept of atoms, calling them "atomos," meaning "uncuttable."
• Aristotle (384-322 BC) rejected Democritus's idea, asserting that all matter consists of five elements: earth, water, air, fire, and aether.

Development of Modern Atomic Theory

• John Dalton (1766-1844) formalized Atomic Theory in 1808, establishing foundational concepts in chemistry.
• Dalton's Atomic Theory includes key principles such as:
  • All matter consists of indivisible and indestructible atoms.
  • Atoms of a given element are identical in mass and properties.
  • Compounds form through combinations of different atoms.
  • Chemical reactions involve rearrangements of atoms.
  • Introduced Laws of Conservation of Mass, Definite Proportions, and Multiple Proportions.

Breakthroughs in Subatomic Particles

• J.J. Thomson (1856-1940) discovered the electron in 1897 using a cathode ray tube, proposing the Plum Pudding Model to illustrate atomic structure, which depicts electrons embedded in a positive sphere.
• Robert Millikan (1868-1953) measured the electron's negative charge through the oil drop experiment, achieved in 1910, and received the Nobel Prize in Physics in 1923.

Landmark Discoveries in Nuclear Structure

• Ernest Rutherford (1871-1937) identified the atomic nucleus via the Gold Foil Experiment in 1911, earning the Nobel Prize in Chemistry in 1908 for his contributions to radioactivity.
• Niels Bohr (1885-1962) introduced the Bohr Model in 1913, demonstrating that electrons orbit the nucleus in defined paths and can transition between energy levels.

Quantum Theories and Neutron Discovery

• Erwin Schrödinger (1887-1961) developed the quantum mechanical model in 1926, focusing on the probability of electron location, and formulated the Schrödinger equation, winning the Nobel Prize in Physics in 1933.
• James Chadwick (1856-1940) discovered neutrons in 1932, significantly enhancing the understanding of atomic structure, leading to a Nobel Prize in Physics in 1935.