Question

How did Mendeleev know that there must be undiscovered elements and how
did he take this into account when he designed his periodic table? ​

Answer 1

Answer:

Mendeleev left gaps in his table to place elements not known at the time. By looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements. ... The element germanium was discovered later.

Explanation:

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Answer 2

Answer:

Mendeleev left gaps in his table to place elements not known at the time. By looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements.