MCQ Detailed View

The nucleus of an atom was discovered by Ernest Rutherford in 1911 through his famous gold foil experiment. Before this discovery, the widely accepted atomic model was J. J. Thomson’s “plum pudding model”, which suggested that positive charge and electrons were spread uniformly throughout the atom.

Rutherford’s experiment involved directing a stream of alpha particles (positively charged helium nuclei) at a very thin sheet of gold foil. Most of the alpha particles passed through the foil without deflection, but a few were deflected at large angles, and some even bounced back. This was unexpected according to the plum pudding model.

Based on these observations, Rutherford concluded that an atom’s positive charge and most of its mass were concentrated in a small, dense, central region, which he called the nucleus. Electrons were thought to orbit this nucleus, similar to planets orbiting the sun. This led to the Rutherford atomic model, which replaced the earlier theory and laid the foundation for modern nuclear physics.

The other scientists mentioned in the options contributed to atomic theory but did not discover the nucleus:

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  Goldstein: Discovered canal rays (positive rays), leading to the identification of protons.

  
  


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  James Chadwick: Discovered the neutron in 1932.

  
  


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  J. J. Thomson: Discovered the electron in 1897.

  
  

Rutherford’s discovery was groundbreaking because it revealed that atoms are mostly empty space with a tiny, massive nucleus containing protons (and later found to contain neutrons). This understanding helped explain atomic structure, radioactivity, and nuclear reactions.