Summarize Mendeleev and Moseley's contributions to the history of the periodic table.

Answer: According to Moseley, similar properties recur periodically when elements are arranged according to increasing atomic number. Atomic numbers, NOT weights, determine the factor of chemical properties.

Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a "periodic" way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table