Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869. Dmitri Mendeleev was born at Tobolsk, Siberia in 1834 and died in 1907.

Mendeleev, the addon, adds all kinds of information on top of the information provided by Blizzard to almost all item tooltips. It is currently not in a state where I'd consider it ready for general use; but if you want to try it out then go ahead! :)

It also depends on the ancient LibPeriodicTable, which frankly is no longer maintained or properly updated. Perhaps things will move forward and get fixed for Cataclysm, but perhaps not.

If, however, you wish to file a ticket to request a feature or report a bug, you're most welcome to do so on the project page for Mendeleev on wowace.com.