The difference between Mendeleev’s and Long-form of periodic table are:
Mendeleev’s periodic table
- Elements have been arranged in order of increasing atomic mass.
- There are only nine vertical columns called groups.
- All the transitional elements are arbitrarily placed together in single group VIII.
- The inert gases were not known at the time of Mendeleev.
- No proper places are assigned to isotopes of elements.
- Dissimilar metals are placed together.
- There are misfit anomalous pairs on the basis of atomic mass.
Long-form of periodic table
- Elements have been arranged in the order of increasing atomic number.
- There are eighteen vertical columns, called groups.
- The inert gases have been placed at the periods 1 to 6 i.e. O (group)
- Isotopes of elements are assigned the same place as their respective elements as they have same atomic number.
- Dissimilar metals are placed in separated sub groups.
- The misfit anomalous pairs have been removed, when atomic number is taken as the basis of classification.