Merits are as follows:-
1. There was a regular gradation in physical and chemical properties of elements.
2. The group number of an element indicates highest oxidation state that it can attain.
3. There were many vacant spaces in Mendeleev's periodic table for the elements to be discovered. He named them Eka-Boron, Eka-Aluminium and Eka-silicone He also predicted the properties of these undiscovered elements including atomic masses. These elements were discovered as Sc ,Ga and Ge with same features as he predicted.
4. Mendeleev’s arrangement helped to correct atomic masses of a number of elements.

Demerits are as follows:-
1. The elements, if arranged according to their atomic weights show an evident periodicity of properties.
2. Elements which are similar as regards their chemical properties have atomic weights which are either nearly the same value or which increase regularly.
3. The arrangement of the elements or of groups of elements in the order of their atomic weights, corresponds with their so called valencies.

• Predictive Power: Mendeleev's periodic table had great predictive power. He was able to predict the properties of elements that had not yet been discovered and left gaps in his table for those elements.


• Organization: The table organized elements based on their atomic mass and grouped elements with similar properties together, making it easier to study and understand the properties of elements.


• Discovery of New Elements: The periodic table helped in the discovery of new elements as it provided a systematic way to organize elements and identify gaps in the table where new elements could exist.


• Classification: Mendeleev's periodic table classified the elements into groups with similar properties, which made it easier to understand and study the behavior of elements.


• Scientific Basis: The periodic table was based on scientific observations and experiments, making it a reliable tool for scientists to use.

• Position of Hydrogen: Hydrogen was placed in a group of its own, despite having properties that are similar to both alkali metals and halogens. This made it difficult to classify and understand the properties of hydrogen.


• Atomic Mass and Number: Mendeleev's periodic table was based on atomic mass, but it was later discovered that atomic number is a more fundamental property of elements. This led to the development of a new periodic table based on atomic number.


• Isotopes: Mendeleev's periodic table did not account for isotopes, which are elements with the same number of protons but different numbers of neutrons. Isotopes have different atomic masses, so they should be placed in different positions on the periodic table.


• Transition Metals: The transition metals were not placed in a separate group in Mendeleev's periodic table, but were scattered throughout the table. Later periodic tables placed the transition metals in a separate block, making it easier to study their properties.


• Limitations: Mendeleev's periodic table had limitations and could not explain all the properties of elements. It was later improved upon by other scientists, leading to the development of more accurate and comprehensive periodic tables.

Overall, Mendeleev's periodic table was a remarkable achievement that greatly advanced the field of chemistry. Despite its limitations, it provided a foundation for the development of more accurate and comprehensive periodic tables that are still used today.