The Modern Periodic Table

THE MODERN PERIODIC TABLE

❝ If elements are arranged according to their ascending order of atomic number, their chemical properties repeat in periodic manner❞.

In order to make the periodic table more useful and accrue, a few improvements were made by Mosley in the Mendeleev,s periodic table.

IMPROVEMENT IN MENDELEEV,S PERIODIC TABLE: 

(1) After the discovery of x-rays, Mosley in (1931) discovered the atomic number of elements. "Atomic number is the number of protons present in the nucleus of an atom"
According to Mosley, atomic number is the fundamental property of an element while atomic masses  is not is not a fundamental property, as one element has different atomic masses for different isotopes. Hence periodic table was rearranged according to ascending order of  atomic numbers. This improvement which was made by Mosley, was called modern periodic law. According to modern periodic law:

❝ If elements are arranged in the ascending order of their atomic numbers , their chemical properties repeat in a periodic manner.❞

(2) An other improvement was the addition of an extra group (group VIII) at the extreme right of the Periodic Table. This group contains noble gases, which had not been discovered in Mendeleev,s time.

(3) An other confusion in Mendeleev,s table was that elements like Be, Mg, Ca, Sr, Ba, Zn, Cd, and Hg were placed in one vertical group, while according to their properties , they belonged to two different categories. The same was true for so many other elements placed in the same vertical group. In modern Periodic Table, the confusion was removed by introducing two types of vertical groups, A and B. In modern periodic table Be, Mg, Ca, Sr and Ba are placed in group IIA and Zn, Cd, Hg in group IIB.

(4) Position of isotopes was adjusted because the periodic table was based on atomic number.

(5) Position of Lanthanides and actinides was also adjusted.