Final answer:
Henry Moseley, in 1913, identified that elements should be ordered according to atomic number rather than atomic weight, by studying the x-ray spectra of elements. This discovery led to the modern arrangement of the periodic table and remains a fundamental aspect of chemistry.
Step-by-step explanation:
The scientist credited with the realization that elements should be ordered by atomic number instead of atomic weight is the English physicist Henry Moseley in the year 1913. Moseley's groundbreaking work involved studying the x-ray spectra of elements and observing the relationship between the x-ray wavelength and atomic number. It was through these observations that he established atomic number as the defining characteristic of an element, marking a fundamental change in how the elements were arranged in the periodic table. Unlike Mendeleev’s periodic table, which was organized by increasing atomic mass and had some discrepancies, Moseley's arrangement based on the atomic number resolved these inconsistencies.
Moseley determined that the atomic number correlates with the number of protons in an atom's nucleus and that this more accurately reflects the properties of the elements. This discovery led to the modern periodic law that elements, when arranged by increasing atomic number, show a periodic pattern in their chemical and physical properties. His findings were supported by the mismatched position of elements like iodine and tellurium in Mendeleev’s table, which, when ordered by atomic number, were corrected. Moseley’s hypothesis was tragically cut short due to his untimely death in World War I, but his legacy remains a cornerstone of modern chemistry.