Development of the model of the atom

Early Beliefs about the Atom:

Before the discovery of the electron, atoms were thought to be indivisible, solid spheres with no internal structure.

The Plum Pudding Model:

Discovery of the Electron: Led to the development of the plum pudding model.
Model Description: The atom was described as a ball of positive charge with embedded negative electrons, similar to raisins in a pudding.
This model was a significant step forward but was eventually replaced as new evidence emerged.

The plum pudding and nuclear models of the atom.

The Nuclear Model and The Alpha Particle Scattering Experiment:

Conducted by: Ernest Rutherford and his team.
Experiment: Alpha particles were fired at a thin sheet of gold foil.
Observations:
- Most alpha particles passed straight through.
- A small number were deflected at large angles.
Conclusions:
- The mass of the atom is concentrated at a small, dense, positively charged center (the nucleus).
- Most of the atom is empty space.
This led to the nuclear model of the atom, which replaced the plum pudding model.

Overhead view of the alpha particle scattering experiment.

The Bohr Model:

Proposed by: Niels Bohr.
Improvements:
- Electrons orbit the nucleus at specific distances (energy levels).
- These orbits, or shells, prevent the electrons from spiraling into the nucleus.
Significance: Bohr's theoretical calculations agreed with experimental observations, further refining the atomic model.

Discovery of Protons:

Experiments showed that the nucleus contains smaller particles, each carrying a positive charge. These were named protons.

Discovery of Neutrons:

Conducted by: James Chadwick (1932).
Findings:
- The nucleus also contains uncharged particles called neutrons.
- Neutrons contribute to the mass of the atom but have no effect on its charge.
Impact: This discovery completed the modern understanding of the atomic nucleus.

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