Question

Evidence for existence of mucleus in an atom

Answer 1

It was scientist Ernest Rutherford, who first gave the evidence of presence of nucleus within an atom, based on which other scientists developed the concept..

1. Rutherford performed the Gold Foil Experiment in which:

• A thin gold foil that was only 1000 atoms thick, was placed amidst a fluorescent screen detector.
• Using a source, alpha ray particles (doubly charged helium nuclei) were bombarded at this thin foil of gold.  

    2.  Upon doing so, Rutherford could observe that:

• A few atoms deviated from their original path by a large angle, instead of passing straight through the gold foil.
• 1 in every 12,000 alpha ray particles rebounded back by 180° and traveled straight backwards.

[ NOTE: These are only two observations among three important ones!]

     3. From the above two observations, Rutherford concluded that:

• There must be a positively charged sphere, which had deflected the oppositely charged alpha ray particle.
• The sphere must be where the entire mass of the atom is concentrated, because it had the capacity to rebound even these highly powerful particles.  
• The sphere must occupy a very small region of the atom, because only one in every 12,000 alpha ray particle directly collided with this sphere to strongly rebound.

From this, the evidence for such a sphere known as Nucleus within the atom was derived and developed...