Moseley studied the x-rays emitted from electrons in the first and second energy levels (K and L), which were first suggested by Niels Bohr around the same time as Moseley's experiment was completed. Electrons from either energy level emitted more energy as the elements were treated in succession throughout the Periodic Table. This observation helped scientists explain the periodic trends observed on the Periodic Table and also help resolve the issues of organizing the Periodic Table by atomic masses, as first suggested by Dmitrii Mendeleev.
