number of electrons in orbital shells. As Thomson's model guided Rutherford's experiments, Bohr's model guided Moseley's research. The Bohr model was elaborated upon during the time of the "old quantum theory", and then subsumed by the full-fledged development of quantum mechanics. Related scientific problems As an important example of a scientific model, the plum pudding model has motivated and guided several related scientific problems. Atomic size and scientific constants The plum pudding model with a single electron was used in part by the physicist Arthur Erich Haas in 1910 to estimate the numerical value of the Planck constant and the Bohr radius of hydrogen atoms. Haas's work was the first to estimate these values to within an order of magnitude and preceded the work of Niels Bohr by three years. Mathematical Thomson problem A particularly useful mathematics problem related to the plum pudding model is the optimal distribution of equal point charges on a unit sphere, called the Thomson problem. The Thomson problem is a natural consequence of the plum pudding model in the absence of its uniform positive background charge. References Foundational quantum physics Atoms Electron Periodic table Obsolete theories in physics