Question

(a) Why did Mendeleev leave gaps in his periodic table?
(b) State any three limitations of Mendeleev's classification.
​(c) How does electronic configurations of atoms change in a period with increase in atomic number?

Answer 1

(a) When Mendeleev developed the periodic table, he realized that many elements are missing in the periodic table and yet to be discovered. So, left gaps in his table for such elements and also predicted their properties.

(b) Limitations of Mendeleev's classification:
1. He could not explain the position of isotopes in the periodic table.
2. He could not assign a proper position to the element hydrogen in the periodic table.
3. He failed to explain the wrong order of atomic masses of some elements.

(c) As we move from left to right in a period, the atomic number will increase due to the increase of electrons in the shell.