write the basis of mandeleev's periodic table. Write the
merits and Anomalies of mandeleev's classification
Answers
(a) Merits of Mendeleev's classification of elements:
(i) Mendeleev's periodic law predicted the existence of some elements that had not been discovered at that time.
(ii) Mendeleev's periodic table could predict the properties of several elements on the basis of their positions in the periodic table.
(iii) It could accommodate noble gases when they were discovered.
(b) Anomalies of Mendeleev's classification of elements:
(i) The position of isotopes could not be explained. If the elements are arranged according to atomic masses, the isotopes should be placed in different groups of the periodic table. But, the isotopes were not given a separate place in Mendeleev's periodic table. They were placed at the same place in the table. This placing of the isotopes at the same place could not be explained by Mendeleev's periodic law.
(ii) Wrong order of atomic masses of some elements could not be explained. In Mendeleev's periodic table, when certain elements were put in their correct group on the basis of their chemical properties, it was found that the element with higher atomic mass comes first and the element with lower atomic mass comes later. Mendeleev's periodic law could not explain this abnormal situation of the wrong order of atomic masses.
Answer:
Mendeleev's Periodic table was based on the atomic mass by which elements were repeated after regular intervals. It was also called Mendeleev's periodic law.
The Merits were:
1. It was the first ever classified form of periodic table which gave us an idea about the way it must be created.
2. It rectified many atomic masses of elements like Beryllium.
3. Mendeleev's concept of predicting elements and leaving spaces for them in the periodic table helped our modern scientists to figure out the undiscovered elements.
The Anomalies were:
1. Hydrogen was placed on the 1st group with alkali metals but it also shows properties similar to that of halogens.
2. Potassium was placed before Argon due to having same atomic mass but in that sense it would disturb the series of noble gases.
3. Eighth group was full of anomalies. Apart of osmium, none of the elements were octavalent.
I hope this helps.