as understanding increased
- Plum pudding model (Wikipedia)
The now obsolete plum pudding model was the first scientific model of the atom with internal structure. It was first proposed by J. J. Thomson in 1904 following his discovery of the electron in 1897 and subsequently rendered obsolete by Ernest Rutherford’s discovery of the atomic nucleus in 1911. The model tried to account for two properties of atoms then known: that there are electrons and that atoms have no net electric charge. Logically there had to be a commensurate quantity of positive charge to balance out the negative charge of the electrons, but having no clue as to the source of this positive charge, Thomson tentatively proposed it was everywhere in the atom, the atom being in the shape of a sphere for the sake of mathematical simplicity. Following from this, Thomson imagined that the balance of electrostatic forces in the atom would distribute the electrons in a more or less even manner throughout this hypothetical sphere.
