Development of Atomic Models

Dalton's Solid Sphere Model

• Scientist: Proposed by John Dalton.
• Model Classification: Termed the solid sphere model.
• Structural Conceptualization: The atom is envisioned as a literal, solid spherical ball with no internal subatomic architecture (containing no electrons, protons, or neutrons; noted as no E, P, N).
• Core Postulates and Beliefs:
  • Composition of Matter: All matter is composed of tiny, fundamental particles designated as atoms.
  • Uniformity Within an Element: Atoms belonging to the same element possess identical properties and identical mass.
  • Distinction Between Elements: Atoms of different elements possess different masses and different properties.
  • Compound Formation: Atoms combine in simple whole-number ratios to form chemical compounds.
• Methodology and Experimental Basis:
  • Developed through the study of chemical reactions and observations of how elements systematically combine with one another in definite ratios.
  • Deduced that atoms behave entirely as tiny, solid, indivisible spheres.

Thomson's Plum Pudding Model

• Scientist: Developed by J.J. Thompson.
• Model Classification: Designated as the plum pudding model.
• Primary Discovery: Identified and discovered the electron, recognized as a negatively charged subatomic particle.
• Atomic Architecture:
  • Asserts that an atom is composed of a diffuse sphere of uniform positive charge.
  • Tiny, negatively charged particles (electrons) are embedded throughout this positive sphere.
• Methodology and Experimental Basis:
  • Conducted using the cathode ray tube experiment.
  • Cathode rays were observed to bend toward an applied positive charge, demonstrating conclusively that the rays contained negatively charged particles.

Rutherford's Nuclear Model

• Scientist: Formulated by Ernest Rutherford.
• Model Classification: Known as the nuclear model.
• Structural Discoveries:
  • Established that the atom contains a tiny, dense, positively charged center called the nucleus.
  • Determined that the vast majority of the atom consists of empty space.
• Methodology and Experimental Basis:
  • Derived from the gold foil experiment.
  • Fired positively charged particles directly at an extremely thin sheet of gold foil.
  • Experimental Observations:
  • The vast majority of the positively charged particles passed directly through the foil without hindrance, confirming that the atom is mostly empty space.
  • A small fraction of the particles were deflected at angles or bounced directly back, proving the existence of a concentrated, tiny, dense, positively charged nucleus.

The Bohr Model

• Scientist: Formulated by Niels Bohr.
• Model Classification: Referred to as the Bohr model.
• Electron Configuration and Quantum Levels:
  • Proposed that electrons do not wander freely, but instead occupy specific, quantized energy levels situated around the nucleus.
• Methodology and Mechanism:
  • Developed through the systematic study of hydrogen's light emission spectrum.
  • Energy Transitions:
  • Electrons absorb energy to jump outward to higher energy levels.
  • Electrons release energy when transitioning down to lower energy levels.