About the Catalysts
Mendeleev and Moseley were the two most influential people in the history of the periodic table. There were other scientists from the same eras who developed tables and charts, but each of those had serious flaws. Mendeleev and Moseley are important because it was they who developed the Periodic Table of the Elements as we know it today.
Dmitri Mendeleev was born in Tobolsk, Siberia, Russia in 1834. He studied and taught in St. Petersburg. Mendeleev's perhaps greatest achievement was his arrangement of the chemical elements into an easy-to-use format. He grouped the 63 known elements into periods and groups by atomic mass. Mendeleev noticed holes in the table and so predicted the existence and properties of undiscovered elements. A notable exclusion from his table was the noble gases, which also had not been discovered. Dimitri Mendeleev died in St. Petersburg in 1907.
Henry Moseley was born in Great Britain in 1887. His work with x-ray spectra to study atomic structure helped determine atomic numbers for chemical elements. He discovered isotopes, explaining how atomic mass did not order the elements appropriately. Moseley was the catalyst for the periodic law, a rule stating that the properties of elements are a periodic function of their atomic numbers. Using the atomic numbers, Moseley was able to more accurately position the elements in the periodic table. Moseley's change to the periodic table allowed the few problems with Mendeleev's periodic table to disappear. The modern periodic table is now based on atomic numbers. Moseley was killed in action at Gallipoli in 1915, World War I.
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