Rutherford, van den Broek, and Moseley
Rutherford put forth a theory that the positive charge in the atom must be due to another subatomic parrticle that had yet to be discovered.
Antonius van den Broek, a Dutch physicist, was the first scientist to suggest that the positioning of the element on the Periodic Table is equal to the nuclear charge of an element. The nuclear charge can be defined as the amount of positive charge contained within the nucleus.
Henry Moseley, an English physicist, was the first scientist to provide experimental evidence for the claims of both Rutherford and van den Broek. Moseley studied the energy of x-rays emitted from each successive element on the Periodic Table. He noticed that the energy of the x-rays increased as one went through the known elements of the Periodic Table. He explained this observation by stating that each successive element must contain a larger positive nuclear charge. The original results of his experiment can be found here.
Rutherford, in experiments in the middle 1910s, provided the first accepted evidence for the positive subatomic particle. In a cloud chamber consisting of nitrogen gas, alpha particles were introduced. The process resulted in the nitrogen atoms transmuting into oxygen atoms, and the detectors also indicated the presence of hydrogen nuclei. With similar results obtained in other cloud chambers with different elements, Rutherford concluded that the nuclei of all elements must contain the same subatomic particle found in the lightest element (hydrogen). He called these subatomic particles protons.
