PERIODIC CLASSIFICATION

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 PERIODIC TABLE :-

The method of arranging similar elements in one group and separating them from dissimilar elements is called classification of elements. 

A table which has been formed by the classification of elements is known as periodic table. 

Mendeleev's Periodic Table :-

Mendeleev arranged sixty three elements in a table on the basis of periodic law, which states that physical and chemical properties of the elements are the periodic function of their atomic masses i.e. when elements are arranged in the increasing order of atomic masses similar elements are repeated after regular intervals. 

Advantages of Mendeleev's periodic table 

(1) Prediction of new element :- In Mendeleev's periodic table there were many vacant spaces. He had predict the properties of elements that would occupy when discovered. When few elements were later discovered they were found to be similar properties as predicted by Mendeleev. 

Ex :-  Elements like Gallium ( eka-aluminium) and Germanium (eka-silicon) we're further discovered. 

(2) Correction of atomic masses 

On the basis of Mendeleev's periodic table atomic masses of certain elements were corrected. 

Ex :- Atomic mass of Be was found to be 13.5 which should be placed after carbon whose atomic mass is 12 . But later Mendeleev determined its valency, equivalent mass and exact atomic mass which was found to be 9.

Disadvantages of Mendeleev's periodic table

(1) Anomalous position 

When elements are arranged in the increasing order of atomic mass. Potassium should come before Argon and Nickel should come before Cobalt. But these elements are written in their most suitable position on the basis of the properties. 

(2) Position of triads 

The elements in the triad like Iron, Cobalt, Nickel are so similar that they should be placed at one group. In this table the place for one element is occupied by three elements. 

(3) Dissimilar elements  placed together

There is difference in property of element of sub group IA and IB. But they are placed in one group. 

(4) Position of lanthanides and Actinides

Lanthanides and Actinides are placed separately in the periodic table which is against the periodic law. 

Can't distinguished between metal & non-metals. 

(5) Position of Isotopes

In Mendeleev's periodic table there were no place for Isotopes which have different atomic mass. 











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