Question

How did Mendeleev arrange the elements . He left empty places in this periodic table why ? . Explain the limitations of Mendeleev classification

Answer 1

$\huge\star{\green{\underline{\mathfrak{Answer :-}}}}$

• Mendeleev arrange all the elements that were known at his time according to the increasing atomic masses and according to similar chemical and physical properties.

• He left empty spaces in his periodic table because he thought that there would be some new elements discovered in future.

• He predicted these new elements and their properties and even name them. For example, Eka Boron - Scandium, Eka aluminium - Gallium and Eka Silicon - Germanium.

• The limitations of the table are :-

1. Anomalous position of hydrogen : no fixed position can be assigned to hydrogen in the periodic table.
2. Position of isotopes : in Mendeleev's periodic table elements are arranged in increasing order of their atomic masses and isotopes of an element have different atomic masses, therefore they should be placed at different positions in the periodic table.
3. Anomalous position of some pairs of elements : like Cobalt with higher atomic mass was placed before Nickel with low atomic mass.
4. No resemblance of elements within subgroups : for example Li,Na,K,Rb and Cs present in first A group are quite different from the coinage metals such as Cu,Ag and Au present in group first B.
5. Uncertainty introduction of new elements : As atomic mass can be in decimals so it is difficult to predict about the number of undiscovered elements.

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