Atoms Test - 3

This atom model was proposed by JJ Thomson before the discovery of the atomic nucleus. When Thomson discovered the negative electron, he realized that atoms had to contain some positive charge material equal to the negative electrons – otherwise the atom wouldn't be electrically neutral. According to this model, the positive charge of the atom is uniformly distributed throughout the volume of the atom and the negatively charged electrons were embedded in it like seeds in a watermelon.

There is an intimate relationship between the internal structure of an atom and the spectrum of radiation emitted by it.

This expectation was based on the knowledge of the "Plum pudding model", proposed by JJ Thomson, where the positive charge and the negatively charged electrons were distributed throughout the whole atom. According to this model, all the alpha particles in the beam should pass through the foil without much scattering. However this experiment of Geiger-Marsden proved the Thomson's model wrong. 

The electrons revolve round their permitted orbits with acceleration and continuously radiate energy in the form of electromagnetic waves. Due to this continuous loss of energy, they would spiral inward and eventually fall into the nucleus.(Classical theory)

All the alpha particles were expected to pass through the gold foil with very little or no scattering, according to the JJ Thomson's "Plum pudding model". 

Most of the alpha particles were deflected through small angles (atleast by 1 degree), some were scattered through larger angles and some rebounced back through angles greater than 90 degrees.

Ernest Rutherford who was a former research student of JJ Thomson supervised the experiment carried by two of his students Hans Geiger and Ernst Marsden. Rutherford felt that there existed a nucleus at the centre of the atom having positive charge and thus proposed the Rutherford model.