Timeline of Atomic Theory

Ancient Philosophers

• Democritus (c. 460 – c. 370 BC)
  • Introduced the concept of atoms as uncuttable particles ("atomos").
  • Suggested all matter is made of these particles in different sizes and shapes.
  • Imagined atoms with specific features:
    • Iron atoms had hooks for strong connections.
    • Salt atoms had spikes, explaining the sharp taste of salt.
• Aristotle (384 – 322 BC)
  • Proposed matter was made up of elements: earth, water, air, fire, and ether.
  • His popularity led to widespread acceptance, overshadowing Democritus.

The Rise of Scientific Experiments

• John Dalton (1808)
  • Conducted experiments proving matter is made of tiny particles (atoms).
  • Imagined atoms as indivisible and in various combinations, resembling tiny balls.
• J.J. Thomson (Late 1800s)
  • Discovered electrons, challenging Dalton's indivisibility.
  • Proposed the Plum Pudding Model:
    • Atoms consist of electrons embedded in a positively charged substance (like a blueberry muffin).

Advancements in Atomic Models

• Ernest Rutherford (Gold Foil Experiment)
  • Discovered the nucleus, showing that positive charge is concentrated at the center.
  • Proposed the Nuclear Model of the atom, contrasting Thomson's model.
• Niels Bohr (1913)
  • Suggested electrons move in circular orbits around the nucleus, similar to planets around the sun.
• Erwin Schrödinger (1920s)
  • Introduced the concept of quantum mechanics.
  • Proposed that electrons do not move in fixed orbits but rather in probabilistic orbitals (hyperactive behavior).
  • Orbitals sketch out different shapes (spheres, teardrop shapes).

Subatomic Particles in the Nucleus

• Ernest Rutherford (1919)
  • Discovered protons, confirming their presence in the nucleus.
• James Chadwick (1932)
  • Discovered neutrons, completing the understanding of the atomic nucleus.

Current Understanding of Atoms

• The Quantum Mechanical Model is the most accurate representation of atomic structure.
• Atoms consist of:
  • Protons and neutrons in the nucleus.
  • Electrons in various orbitals around the nucleus.

Simplifying Atomic Discussions

• While the quantum mechanical model is accurate, simpler models (like Bohr’s) may be used for ease of understanding, especially in discussions of bonding.
• Important to remember that these simplifications do not fully represent the complexity of atomic behavior.