How did the Periodic Table become organized the way it is with the elements arranged in groups or families with similar valence shells and periods with the same number of principal energy levels? This Powerpoint presentation explores the historical development of the Periodic Table from Mendeleev to Mosely. It reviews Mendeleev's discovery of periodicity when the elements were arranged by mass, and the inconsistencies of Mendeleev's arrangement. Then it explores how Mosely refined Mendeleev's ideas to develop the modern Periodic Table.
Free materials on this topic are available on my website at http://evanschemistrycorner.com.