Mendeleev did not predict the existence of noble gases. In fact, the discovery of noble gases came after the development of Mendeleev's periodic table. Here's why:

* Mendeleev's table was based on the elements known at his time: The noble gases (Helium, Neon, Argon, Krypton, Xenon, Radon) were not discovered until the late 19th century.

* Chemical properties: The noble gases are incredibly unreactive, making them difficult to detect and isolate using the techniques available in Mendeleev's time.

* The periodic table evolved: After the discovery of noble gases, the periodic table was modified to accommodate them, highlighting the need for a new group with unique properties.

It was William Ramsay, not Mendeleev, who discovered the noble gases in the late 19th century, leading to the expansion of the periodic table.