Mendeleeves Periodic table and its defects

Mendeleev Periodic Table – As we all are aware that there are 118 elements present in our periodic table. In this 94 elements are natural elements and 24 elements are synthetic elements. In the early year 1800, only 30 elements were known. As the more elements are discovered, remembering the elements and their properties were very hard for the scientists. They started gathering information about the elements and started categorizing it. The categorization of elements in a tabular form according to their properties became popular. The tabular form structure in which various elements are arranged according to their properties is known as the periodic table.

Mendeleeves Periodic table and its defects

Mendeleev's Periodic Law

The physical and chemical properties of the elements (as well as the formula and properties of their compounds) are the periodic function of their atomic weight (atomic masses).

Following two inferences can be drawn from this periodic law.
  • The physical and chemical properties of the elements depend upon their atomic masses.
  • The dependence of physical and chemical properties of elements upon their atomic masses is periodic.






Mendeleev's Periodic Table

On the basis of this periodic law, Mendeleev arranged all the elements known at that time in the form of a table which is now known as Mendeleev's Periodic Table. In this table, the elements were arranged horizontally in ten series in the order of their increasing atomic weights. These series were divided into seven horizontal and eight vertical columns. The horizontal columns were called periods while the vertical columns were named as groups. Mendeleev tried to place the elements having similar properties in the same group. At several places he ignored the order of atomic masses in order to group together the elements having similar properties.

The important features of the modified form of periodic table are as follows :- 

i) Series : All the known elements have been arranged in ten horizontal columns called series.

ii) Groups : There are nine vertical columns in the periodic table, these are called groups.

iii) Periods : The ten horizontal series have been arranged in seven horizontal columns called periods.


Original view of Mendeleev's Periodic Table


Defects Of Mendeleev's Periodic Table


In spite of the remarkable contributions made to chemistry, Mendeleev's periodic table had certain defects. These defects are as follows :-


1) Position Of Hydrogen

The position of Hydrogen is not fixed. It was considered in Group IA as well as in Group VIIA, because it forms a positive ion as in HCl but also a negative ion as in NaH.

2) Metals & Non-Metals

No attempts are made to separate Metals & Non-metals.

3) Positions Of Isotopes

The isotopes of an element are atoms of that element having same atomic number but different mass number. According to Mendeleev’s Periodic Law, isotopes of an element must be given separate places in the periodic table because they have different atomic masses.

4) Similer Elements are separated

Some elements such as copper and mercury or gold and platinum  which posses slimier chemical properties but placed in different groups.

5) Electronic arrangement

It does not explain the Electronic arrangement of atoms.


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