Question

why did mendeleev leave gaps in his early periodic table, and what was the ultimate importance of those gaps

Answer 1

go to:
http://en.wikipedia.org/wiki/Dmitri_Mendeleev

Answer 2

he knew that these elements will be discovered in future nd nt wanted to prove himself wrong by placing other elements on that gaps now new discovered elements can be placed on these gaps without comparing with all elements of periodic table.