History_of_the_atom

Page 1: Solid Sphere Model

• John Dalton, early 1800s

  • Suggested that substances are made of small hard spheres called atoms.

  • Proposed that atoms are indivisible (cannot be split into anything smaller).

  • New substances are formed through the addition and rearrangement of atoms.

  • Ideas remain useful today, with models being used to describe particle arrangements in solids, liquids, and gases.

• Key Concepts:

  • Atoms: Hard spheres.

  • States of Matter: Solid, Liquid, Gas.

Page 2: The Plum Pudding Model

• J J Thomson, early 1900s

  • Discovered the electron through extensive experiments.

  • Modified the solid sphere model to propose that atoms consist of a sphere of positive charge with negatively charged electrons embedded within it.

  • Named this the plum pudding model, likening it to currants in a Christmas pudding.

• Key Concepts:

  • Structure: Sphere of positive charge with embedded negatives (electrons).

  • Analogy: Christmas pudding.

Page 3: Nuclear Model

• Ernest Rutherford, 1909 - 1911

  • Tested the plum pudding model using an experiment where alpha particles were fired at thin gold foil.

  • Most particles passed through without deflection, indicating a lot of empty space within the atom.

  • A small number were scattered in different directions, leading to significant conclusions:

    • The mass of the atom is concentrated in a central region called the nucleus.

    • The nucleus carries a positive charge due to the existence of smaller particles named protons.

  • This nuclear model replaced the plum pudding model.

• Key Concepts:

  • Experiment: Alpha scattering experiment.

  • Observations: Most particles undeflected, some scattered.

  • Discovery: Presence of nucleus and protons.

Page 4: Planetary Model

• Niels Bohr, 1913

  • Contributions from theoretical calculations led to insights about electron arrangements.

  • Proposed that electrons orbit the nucleus within defined shells at fixed distances.

  • Known as the planetary model, this understanding arose from experiments observing light emitted from heated atoms.

• Key Concepts:

  • Structure: Electrons orbiting in shells around a positive nucleus.

  • Inspiration: Light emissions from heated atoms.

Page 5: Atomic Model

• James Chadwick, 1932

  • Conducted experiments providing evidence for the existence of neutrons, which occupy the nucleus alongside protons.

  • This atomic model (neutrons + protons in the nucleus with electrons in orbit) is the current accepted model of atomic structure.

• Key Concepts:

  • Structure: Neutrons and protons in the nucleus; electrons in orbit.

  • Confirmation: Neutron's existence solidified the atomic model.