Thomson
Explanation
The evolution of atomic theory involved several models proposed to explain the internal structure of the atom and the arrangement of subatomic particles. The "plum pudding" model was one of the earliest theoretical descriptions following the discovery of the electron.Analysis of Options:
- Rutherford is incorrect: Ernest Rutherford proposed the Nuclear Model of the atom (Planetary Model) based on the alpha-particle scattering experiment. He established that the positive charge and most of the mass are concentrated in a central nucleus.
- Bohr is incorrect: Neils Bohr proposed the Bohr Model, which postulated that electrons revolve around the nucleus in discrete, fixed energy orbits (shells).
- Thomson is correct: J.J. Thomson proposed the Plum Pudding Model (also known as the watermelon model) in 1898. In this model, the atom is visualized as a sphere of uniform positive charge with negatively charged electrons embedded within it, similar to plums in a pudding or seeds in a watermelon.
- Chadwick is incorrect: James Chadwick is credited with the discovery of the neutron in 1932, which explained the mass of the nucleus but did not constitute a separate atomic structure model in the early sequence of Thomson-Rutherford-Bohr.
Key Takeaway: J.J. Thomson proposed the Plum Pudding Model, which described the atom as a positively charged sphere with embedded electrons to maintain electrical neutrality.