Question

why did mendeleev left gaps in his table?

Answer 1

Mendeleev left gaps in his periodictable because the properties of known elements predicted other, as-yet-undiscovered, elements in these locations. ... He predicted that new elements would be discovered later and they would occupy those gaps.

Answer 2

Mendeleev left gaps in his periodic table because the properties of known elements predicted other, as-yet-undiscovered, elements in these locations.

He predicted that new elements would be discovered later and they would occupy those gaps.