Question

Mendeleev arranged the elements in the order of increasing atomic weights. 

(a) Write down the merits of Mendeleev’s periodic table. 

(b) What are the demerits of Mendeleev’s periodic table?

Answer 1

(a) Merits of Mendeleev’s periodic table:

• Study of elements – Elements are classified into groups with similar properties, thus facilitating the study of properties of elements. 
• Prediction of new elements – Mendeleev left certain vacant places in his table which provided a clue for the discovery of new elements, 

e.g. Eka-AI (for Ga), Eka-Si (for Ge). 

• Determination of correct atomic weights – With the help of this table, doubtful atomic weights of some elements were corrected.

(b) Demerits of Mendeleev’s periodic table:

• Position of hydrogen was not certain. 
• Anomalous pairs of elements – Certain elements of higher atomic weight preceed those with lower atomic weight, 

e.g. I (at.wt.127) was placed after Te (at.wt. 128).

• Lanthanides and Actinides are not given proper places in this periodic table. 
• No proper position for isotopes.