Yes; in his time not every element was known. As every element in the same column (group) has more or less the same chemical properties, he predicted there should be an element that was not yet discovered at some places.
For example, under Silicon, there was a gap where he suspected that, to complete the pattern, a new element was missing; he called it eka-silicon, and correctly predicted many of its properties. The new element was found later, with properties very similar to the predictions; it was eventually called Germanium.
Mendeleev predicted the discovery of other elements and left space for these new elements, namely eka-silicon (germanium), eka-aluminium (gallium), and eka-boron (scandium).
Mendeleev's decision to leave gaps in his Periodic Table was supported by the discovery of gallium.
gallium
Phosphorus
6th and 7th period are the longest period of the perodic table
check out this amazing Perodic table at www.calculatoredge.com
Te = Terbium. Lanthanoid atomic # 65 Mass # 158.92 [Xe] 4f9 6s2
What is the only letter not appearing on the perodic table as a symbol or part of the symbol
A Halogen.
meercury , lead
Copper
Phosphorus
lithium
Most chemists attribute the discovery to Dmtri Mendeleev.
lanthanum is a element on the perodic table ...
J
Francium
Dmitri Mendeleev in 1869
perodic law
Many people were involved in the discovery of the elements. Certain elements have been known since ancient times and man will never know who truly discovered those. There is more information at the related link.