Question

why did Mendeleev's leave some gaps in the periodic table
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Answer 1

Answer:

Mendeleev left spaces in his periodic table because he predicted there were elements that weren't discovered yet that would fit in these spaces.

Answer 2

Answer:

Dmitri Mendeleev is credited with greatly improving one of the first periodic tables. Many times, things are organized by name, such as in an alphabetical filing system. Mendeleev organized the elements by their atomic masses.

Mendeleev left spaces in his periodic table because he predicted there were elements that weren't discovered yet that would fit in these spaces.