Thomson's plum pudding model viewed the atom as a massive blob of positive charge dotted with negative charges.
A plum pudding was a Christmas cake studded with raisins ("plums"). So think of the model as a spherical Christmas cake.
When Rutherford shot α particles through gold foil, he found that most of the particles went through. Some scattered in various directions, and a few were even deflected back towards the source.
He argued that the plum pudding model was incorrect. The symmetrical distribution of charge would allow all the α particles to pass through with no deflection.
Rutherford proposed that the atom is mostly empty space. The electrons revolve in circular orbits about a massive positive charge at the centre.
His model explained why most of the α particles passed straight through the foil. The small positive nucleus would deflect the few particles that came close.
The nuclear model replaced the plum pudding model. The atom now consisted of a positive nucleus with negative electrons in circular orbits around it .