Question

What were the limitations of mendeleev's periodic Table and what were the major achievements of the same?

Answer 1

Mendeleev arranges the elements in the increasing order of their atomic masses. According to Mendeleev, the physical and chemical properties are the periodic function of their atomic mass.

The limitations of Mendeleev's periodic tables are as under:

• Position of hydrogen: The position of a hydrogen atom is uncertain because it show resemblance with alkali metal and halogens. But in Mendeleev's periodic table, Hydrogen is placed with alkali metals in group 1A.
• Position of isotopes: There is no separate position given to the isotopes of an element.
• Cause of periodicity: Mendeleev's periodic table does not explain successfully the cause of periodicity. Some dissimilar elements are placed together.
• Some elements having higher atomic mass are placed before the elements with lower atomic mass.

Achievements of Mendeleev's periodic tables are as under:

• Systematic study of elements:
• As the elements having the same properties are grouped together so it becomes very useful to remember the properties of a large number of elements in a systematic way.

• Prediction of new elements:
• Mendeleev predicted the properties of those missing elements from the known properties of the other elements in the same group.
• On the basis of this, he named Gallium as Eka-Almunium, Germanium as Eka-Silicon, and Scandium as Eka-Boron.

• Correction of atomic mass:
• The atomic mass of beryllium was corrected from 13.5 to 9. The atomic mass of indium, gold, and platinum was also corrected.

• When noble gases were discovered, they could be placed in a new group without disturbing the order.​
• Mendeleev took the formulae of the oxides and hydrides formed by the elements as the basic properties of elements for their classification in the periodic table.