IMPROVEMENTS IN MENDELEEV’S PERIODIC TABLE AND MODERN PERIODIC LAW

     IMPROVEMENTS IN MENDELEEV’S PERIODIC TABLE AND MODERN PERIODIC LAW In 1913, an English scientist, Mosely, discovered atomic number

     Thus following improvements were made in Medeleev’s periodic table

        Elements were arranged in ascending order of their atomic numbers 

    Thus modern periodic law states

                                                  "If the elements are arranged in ascending order of their atomic numbers, their chemical properties repeat in a periodic manner:

•      A Noble gases containing VIII group is introduced at extreme right of periodic table. Noble gases were not discovered in Mendeleev’s time.

•      Mendeleev placed Be, Mg, Ca , Ba and Zn , Cd , Hg in same group. Although their properties are different. Similar was the case of many other elements.

In modern periodic table, this defect was removed by making two subgroups A and B

            Thus 

                           Be, Mg, Ca , Ba are placed in II A group while Zn , Cd , Hg in II B.

GROUPS  

           The vertical columns in the periodic table are called groups.

 All the elements in the same group have similar properties & similar valence electronic configuration.

Alkali Metals  Elements of group IA are called alkali metals

Alkaline Earth Metals           

                                Elements of group IIA are called alkaline earth metals

Halogens        

                Elements of group VIIA are called Halogens

Noble Gases/Inert Gases

           Elements of group VIIIA are called noble gases.