Final answer:
Henry Moseley's discovery in 1913 showed that the order of elements in the periodic table should be based on increasing atomic number rather than atomic mass, leading to the formation of the modern periodic table with elements grouped by similar properties.
Step-by-step explanation:
In 1913, the physicist Henry Moseley made a significant discovery that revolutionized the scientific community's understanding of the periodic table. Moseley found that each element's nucleus had a unique positive charge, and the magnitude of this charge could be determined by the atomic number, which is the number of protons in the nucleus. Consequently, he realized that the periodic table should be arranged in order of increasing atomic number rather than increasing atomic mass.
Before this discovery, the periodic table was organized based on atomic mass, which led to some inconsistencies with the properties of certain elements. Moseley's discovery corrected these anomalies by establishing that the fundamental ordering principle of the periodic table should be the atomic number. Organizing elements by atomic number ensures that elements with similar properties fall into the same groups, leading to the modern periodic table we use today.
Therefore, Moseley's work demonstrated that the order of the elements in the periodic table is effectively determined by the increasing atomic number, confirming that this should be the basis for the structure of the Periodic Law. His work also hinted at the relationship between an element's placement on the table and its electron configuration, which further explains the periodicity in the properties of the elements.