Question

What are the demerits of Mendeleev’s periodic table?

Write the demerits of Mendeleev’s periodic table.

Answer 1

1. Ambiguous Sequence: Cobalt (Co) and nickel (Ni) have the same whole-number atomic mass, causing confusion in their placement order.
2. Position of Isotopes: Isotopes share chemical properties but have different atomic masses, making it difficult to place them in the table.
3. Irregular Mass Increase: The rise in atomic mass between elements is not uniform, making it impossible to predict how many undiscovered elements exist between two heavy elements.
4. Position of Hydrogen: Hydrogen shows properties similar to both alkali metals (Group I) and halogens (Group VII), so its exact position could not be decided.