Final answer:
Mendeleev's periodic table was organized by atomic mass, which led to errors; these were corrected when the organizing principle was changed to atomic number by Henry Moseley.
Step-by-step explanation:
Dmitri Mendeleev and Lothar Meyer independently developed periodic tables based on increasing atomic mass, but Mendeleev is often credited with greater foresight for predicting undiscovered elements and leaving blanks in his table for them. Mendeleev's periodic table, published in 1869, was revolutionary but held errors due to its organization by atomic mass rather than atomic number. These errors were rectified later when Henry Moseley discovered atomic number and reorganized the periodic table accordingly. Moseley's work explained discrepancies and fully illuminated the reasons behind the periodic repetition of chemical properties. The modern periodic table reflects this reordered arrangement, maintaining Mendeleev's original vision while correcting his errors.