Who first proposed the plum pudding model of the atom?

The plum pudding model is one of several historical scientific models of the atom. First proposed by J. J. Thomson in 1904 soon after the discovery of the electron, but before the discovery of the atomic nucleus, the model tried to explain two properties of atoms then known: that electrons are negatively-charged particles and that atoms have no net electric charge.

In this model, atoms were known to consist of negatively charged electrons. Though Thomson called them "corpuscles", they were more commonly called "electrons" which G. J. Stoney proposed as the "fundamental unit quantity of electricity" in 1891. At the time, atoms were known to have no net electric charge. To account for this, Thomson knew atoms must also have a source of positive charge to balance the negative charge of the electrons. He considered three plausible models that would be consistent with the properties of atoms then known:

1. Each negatively-charged electron was paired with a positively-charged particle that followed it everywhere within the atom.

2. Negatively-charged electrons orbited a central region of positive charge having the same magnitude as the total charge of all the electrons.

3. The negative electrons occupied a region of space that was uniformly positively charged (often considered as a kind of "soup" or "cloud" of positive charge).