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J.J. Thomson contributed to the understanding of the atomic structure by discovering the electron and proposing the "plum pudding" model. 1. Discovery of the Electron: In 1897, J.J. Thomson performed cathode ray tube experiments, where he observed that cathode rays were comprised of negatively charged particles, which he called "corpuscles." These particles are now called electrons. Thomson's work proved that atoms have subatomic particles and are not indivisible as previously believed. 2. Plum Pudding Model: After the discovery of the electron, Thomson proposed a model for the atom's structure called the "plum pudding" model. In this model, the atom was assumed to be a sphere of positively charged matter in which electrons were embedded, similarly to plums in a pudding. This was the first theoretical model that included electrons in the atomic structure.

Ernest Rutherford contributed to the understanding of the atomic structure through his gold foil experiment, which disproved the plum pudding model and led to the proposal of the nuclear model of the atom. 1. Gold Foil Experiment: In 1909, Rutherford conducted an experiment where he aimed alpha particles (positively charged particles) at a thin gold foil. According to the plum pudding model, the alpha particles should have passed through the foil with minimal deflections. However, Rutherford observed that a small number of alpha particles were deflected at large angles, some even bouncing back. This result could not be explained by the plum pudding model. 2. Nuclear Model of the Atom: To explain the results of the gold foil experiment, Rutherford proposed a new model called the nuclear model of the atom. In this model, the atom consists of a small, dense, positively charged nucleus at the center, surrounded by electrons orbiting at a distance. The majority of the atom is empty space, which explains why most of the alpha particles passed through the gold foil with minimal deflections. In conclusion, J.J. Thomson's main contribution to atomic structure was the discovery of the electron and his proposal of the plum pudding model, while Ernest Rutherford's major contribution was the gold foil experiment and the subsequent nuclear model of the atom. These pioneers laid the groundwork for our modern understanding of atomic structure.