Henry Moseley made significant changes to the periodic table in the early 20th century, primarily by rearranging the elements based on atomic number rather than atomic mass. This adjustment was based on his experimental work involving X-ray spectra, which led him to determine the atomic numbers of elements more accurately.
Before Moseley, the periodic table was organized by atomic mass, which sometimes resulted in anomalies. For example, elements like iodine and xenon were out of order according to their properties. Moseley’s findings showed that atomic number, which corresponds to the number of protons in an atom’s nucleus, provided a more accurate way to categorize elements. This change not only resolved existing discrepancies but also improved the overall understanding of the periodic relationship among elements.
His work laid the groundwork for modern periodic law and reinforced the importance of atomic structure in chemistry. Ultimately, Moseley’s adjustments ensured that elements were placed in a sequence that better reflected their chemical behavior, leading to a more intuitive and functional periodic table.