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The Evolution of Atomic Theory: From Ancient Philosophies to Modern Discoveries

This timeline chronicles the evolution of atomic theory from its ancient origins to contemporary scientific advancements. Beginning with Democritus circa 400 B.C.E., who posited that matter is made of indivisible particles, the timeline highlights contributions from Aristotle, alchemists, and key figures such as John Dalton, Antoine Lavoisier, and Marie Curie. It showcases pivotal experiments like the Gold Foil experiment by Ernest Rutherford and advances in quantum mechanics by scientists like Niels Bohr and Erwin Schrödinger. This historical perspective reveals the dynamic journey of understanding matter.

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The Evolution of Atomic Theory: From Ancient Philosophies to Modern Discoveries

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  1. Timeline of the AtomFrom “Atomos toClouds”

  2. Democritus • 400 B.C.E. • Proposed that matter was composed of tiny indivisible particles • Based on thought not experimentation • Greek: “atomos”

  3. Aristotle • 350 B.C.E. • 4 element theory • Matter infinitely divisible • All matter made of different amounts of the 4 elements

  4. Alchemists • 500BCE to 1720 • Mixture of science and mysticism. • Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

  5. Sir Francis Bacon • 1620’s • Hypotheses based on evidence, experiments • Scientific Method • The birth of science as we know it

  6. Benjamin Franklin • 1700’s • Experiments with electricity • Arbitrarily decides positive and negative charge • Attraction between opposing charge

  7. Antoine Lavoisier • 1777 • Isolated “Elements” that could not be broken down further • Father of Modern Chemistry • Theorized how elements become compounds • Famous for parlor tricks

  8. Charles Augustin de Coulomb • 1780’s • Some fluids repelled, some attracted • Idea of charge

  9. John Dalton • 1803 • Water same Everywhere • Compounds happen in definite whole number ratios • Atomic Theory • Disproved Alchemy

  10. Daltons Atomic Theory Postulate 1 Postulate 2 All matter is made of atoms A chemical reaction is a rearrangement of atoms All atoms of an element are identical in mass and property Compounds are formed of two or more types of elements Atoms are indivisible and indestructible Postulate 3 Postulate 4 Postulate 5

  11. Sir William Crookes • 1870’s • Cathode Ray Tube (CRT) • Later used to find electrons

  12. Henri Becquerel • 1896 • Accidentally discovered Radiation • Set up experiment on photo plates but was exposed before light hit them

  13. Marie and Pierre Curie • 1898 • Defined radiation as atoms breaking down and emitting parts spontaneously • Discovered many radioactive elements

  14. JJ Thomson • 1898 • Discovered Crooke’s beam was negatively charged by deflecting with a magnet • Discovered the beam was particles by including paddlewheel

  15. JJ Thomson • Plum Pudding Model • Raisin Bread Analogy

  16. Max Planck • 1900 • Energy is emitted in small discrete amounts he called quanta • Planck’s constant

  17. Albert Einstein • 1905 • Special Theory of Relativity • Particle Nature of Light

  18. Robert Milikan • 1910 • Found Charge of e- • Oil Drop Experiment

  19. Ernest Rutherford • 1909 - 1911 • Gold Foil Experiment • Plum Pudding?????

  20. Gold Foil Experiment • Experiment Animation

  21. Rutherford Model • Nuclear Model • dense, positive nucleus surrounded by negative electrons

  22. Neils Bohr • 1913 • Bright-Line Spectrum • tried to explain presence of specific colors in H spectrum • Energy Levels • electrons can only exist in specific energy states

  23. Neils Bohr • Bright-Line Spectrum • Planetary or Solar System Model • electrons move in circular orbits within specific energy levels

  24. Louise DeBroglie • 1924 • Research in Quantum Theory • Particle/Wave Duality • “Wavicle or Partave”

  25. Erwin Schrodinger • 1926 • Wave nature of e- • The beginning of Quantum Mechanical Model of aton • New Problems

  26. Erwin Schrodinger • Quantum mechanics • electrons can only exist in specified energy states • Electron cloud model • orbital: region around the nucleus where e- are likely to be found

  27. Erwin Schrodinger Electron Cloud Model (orbital) • dots represent probability of finding an e-not actual electrons

  28. Schrodinger’s Cat

  29. James Chadwick • 1931 • Finds mass of Proton • Irene Joliot Curie • 1931 • Finds Neutron

  30. Glen Seaborg • 1951 • Transuranic Elements

  31. Murray Gell-Mann & George Zweig • 1964 • Particles in Protons & Neutrons • 6 types

  32. He Murray Gell-Mann & George Zweig less mass more mass • 3 quarks = 1 proton (2+, 1-) or 1 neutron (1+, 2-)

  33. What Does the Future Hold?

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