Question

____________ is an element for which Mendeleev had left a blank space in his periodic table, assuming it would be discovered in the future.

Answer 1

• In Mendeleev's periodic table, elements with similar properties are arranged together.
• He assumed there must be missing elements and assumed they would be discovered in the future.
• So, he left a blank place for undiscovered elements.
• In the modern periodic table, Scandium$\left(\mathrm{Sc}\right)$ was invented based on properties from Boron$\left(\mathrm{B}\right),$ Gallium$\left(\mathrm{Ga}\right)$ was invented based on properties from Aluminium$\left(\mathrm{Al}\right)$, and Germanium$\left(\mathrm{Ge}\right)$ was invented based on properties from Silicon$\left(\mathrm{Si}\right)$.

Hence, Scandium$\left(\mathrm{Sc}\right)$, Gallium$\left(\mathrm{Ga}\right)$, and Germanium$\left(\mathrm{Ge}\right)$ are the elements for which Mendeleev had left a blank space in his periodic table.