Final answer:
James Chadwick expanded on Rutherford's model by discovering the neutron, which explained the discrepancy between the number of protons and atomic weights of the elements, enriching our understanding of the atom's substructure.
Step-by-step explanation:
James Chadwick's model of the atom contributed significantly to the understanding of atomic structure by confirming the existence of neutrons. Chadwick's work followed the Rutherford model, which depicted the atom similarly to a solar system with electrons orbiting around a central nucleus. While Rutherford's model suggested a tiny, dense, positively charged nucleus, it could not explain the atomic weight of elements, since not all mass could be accounted for by the presence of protons alone.
In 1932, Chadwick performed experiments bombarding beryllium with alpha particles, which led to the discovery of a new, uncharged particle - the neutron. This discovery explained the missing mass in the nucleus that protons alone could not account for. By proving the existence of neutrons, Chadwick's model resolved the discrepancy between the number of protons and the atomic weight of elements and furthered our comprehension of the atom's substructure. With neutrons in the atomic model, the understanding of atomic stability, isotopes, and the chemical properties of elements was greatly enhanced.
Overall, Chadwick's work expanded the Rutherford's planetary model and advanced our understanding of the atom, ultimately contributing to the development of quantum mechanics and setting the stage for subsequent discoveries in particle physics.