The plum pudding model conceptualized the atom as a sphere of positive charge, with negatively charged electrons embedded within it.

This model was introduced by J.J. Thomson in $1904$, following his discovery of the electron. It aimed to explain the atomic structure by incorporating these tiny, negatively charged particles. The name ‘plum pudding’ was inspired by the traditional British dessert, where the plums represent the electrons and the pudding signifies the positive charge.

In the plum pudding model, the atom was depicted as a large sphere with an overall positive charge. The negatively charged electrons were distributed throughout this sphere, akin to plums scattered in a pudding. The atom was assumed to be electrically neutral, meaning that the positive and negative charges balanced each other out. This balance was achieved because the number of negatively charged electrons was equal to the positive charge within the atom.

However, the plum pudding model was ultimately disproven by Ernest Rutherford’s gold foil experiment in $1911$. His findings demonstrated that the positive charge and the majority of the atom’s mass were concentrated in a small central nucleus, with electrons orbiting around this nucleus. This led to the formulation of the nuclear model of the atom. Despite its inaccuracies, the plum pudding model was a crucial advancement in the evolution of atomic theory, as it was one of the first models to suggest that atoms are composed of smaller subatomic particles.