Question

Write the merits of the modern periodic table over Mendeleev's Periodic table.

Answer 1

There are several attempts to classify the elements. Out of these, the Modern periodic table is the most successful attempt as it is based on the fundamental property of the elements.

Complete answer:
The modern periodic table show the following advantages over Mendeleev’s periodic table:
(1) In the modern periodic table, the classification of elements is based on the atomic number. However, in the case of Mendeleev’s periodic table, the elements are arranged in the increasing order of the atomic weight. Atomic number is a more fundamental property as compared to atomic weight. The physical and chemical properties of the elements are the periodic function of the atomic numbers and not atomic weights.
(2) There is no discrepancy in the position of Isotopes-
An element has several isotopes. These isotopes have the same number of protons, same, number of electrons and same atomic number. Hence, they are placed in the same position in the modern periodic table. However, in the case of Mendelev’s periodic table, if you were to put isotopes, then you need different positions.
(3) There is no anomaly in the position of Argon and Potassium in the modern periodic table. However, in the Mendeleev’s periodic table, the positions of argon and potassium are ambiguous.
Argon has an atomic number of 18 and mass number of 40. Potassium has the atomic number of 19 and the mass number of 39.
As per the modern periodic law, you need to arrange the elements in the increasing order of their atomic number.
So, you should first place argon, having lower atomic number, followed by potassium having higher atomic number.
(4) In the modern periodic table, the lanthanides and actinides have been separately placed at the bottom of the periodic table.

Note: In the modern periodic table, there are 18 columns and 7 rows. Each column is called a group and each row is called a period. Thus, the modern periodic table has 18 groups and 7 periods.