what are the limitation of mendeleev periodic table

Mendeleev’s Periodic Table was one of the earliest attempts to classify elements based on their atomic masses and chemical properties. Although it was a major achievement in chemistry, the table had several limitations that were later solved by the modern periodic table.

One major limitation was that hydrogen did not have a fixed position. Hydrogen shows properties similar to both alkali metals and halogens, so its placement in the table remained uncertain.

Another limitation was related to isotopes. Isotopes are atoms of the same element with different atomic masses. Since Mendeleev arranged elements according to atomic mass, isotopes could not be placed properly in his table.

The increasing order of atomic masses was also not strictly followed in some cases. For example:

• Cobalt has a higher atomic mass than nickel but was placed before nickel to match chemical properties.

• Tellurium and iodine also violated the atomic mass order.

The table also could not explain the cause of periodicity in elements because the concept of atomic number was not known at that time.

Noble gases were not included in the original periodic table because they had not yet been discovered.

Major Limitations of Mendeleev Periodic Table:

Limitation	Explanation
Uncertain position of hydrogen	Similar properties with two groups
No place for isotopes	Based on atomic mass
Incorrect atomic mass order	Some elements violated order
No explanation of periodicity	Atomic number was unknown
Noble gases absent	Not discovered at that time

In conclusion, Mendeleev’s periodic table laid the foundation for modern chemistry, but its limitations led to the development of the modern periodic table based on atomic numbers.