What is the Difference Between Mendeleev and Modern Periodic Table?

The main difference between Mendeleev's periodic table and the modern periodic table lies in the basis for arranging the elements. Here are the key differences:

1. Basis for Arrangement: Mendeleev's periodic table is based on atomic mass, while the modern periodic table is based on atomic number.
2. Number of Elements: Mendeleev's periodic table contains about 63 elements, whereas the modern periodic table contains about 118 elements.
3. Undiscovered Elements: In Mendeleev's periodic table, there were gaps for undiscovered elements, while the modern periodic table maintains uniformity.
4. Noble Gases: Noble gases were not placed in Mendeleev's periodic table (as they were not discovered at that time), but they are placed in a separate group (group-18) in the modern periodic table.
5. Transition Elements: In Mendeleev's periodic table, transition elements were included with other elements, while in the modern periodic table, transition elements are placed in a separate block.

In summary, Mendeleev's periodic table was a pioneering work that laid the foundation for the modern periodic table. The modern periodic table is based on atomic number and has expanded to include many more elements, providing a more accurate and comprehensive understanding of the periodic behavior of elements.

Comparative Table: Mendeleev vs Modern Periodic Table

Here is a table comparing the differences between Mendeleev's periodic table and the modern periodic table:

Mendeleev's periodic table was based on atomic mass and contained about 66 elements, with gaps for undiscovered elements. In contrast, the modern periodic table is based on atomic number and contains about 118 elements, with no gaps. Noble gases, which were not included in Mendeleev's periodic table, are now placed in a separate group called Group 18. Additionally, transition elements are now placed in a separate block in the modern periodic table.