Question

what are the limitations of mendeleev's periodic table ?​

Answer 1

Limitations of mendeleev’s classification :

(i) He could not assign a correct position of hydrogen in his periodic table, as the properties of hydrogen resembles both with alkali metals as well as with halogens.

(ii) The isotopes of the same element will be given different position if atomic number is taken as basis, which will disturb the symmetry of the periodic table.

(iii) The atomic masses do not increases in a regular manner in going from one elements to the next.

Answer 2

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Explanation:

In Mendeleev’s periodic table, the noble elements were not included in the table as they were not discovered at that time.

In Modern periodic table, the noble elements were placed in group 18 as a last and separated group.

In Mendeleev’s periodic table, elements with larger atomic weights were placed before elements with smaller atomic weight without any justified reason.

In modern periodic table, all were arranged systematically with increasing atomic number and weight too.

In Mendeleev’s periodic table, some different elements were grouped together while some similar elements were placed in different groups. Ex: alkali metals like Li , Na, K were placed with coinage metals Cu, Ag, Au etc.

In Modern periodic table there was no such confusion, the coinage metals have their own position in d-block and alkali metals are placed in s-block elements.

In Mendeleev’s periodic table, the isotopes were placed in different positions.

In Modern periodic table, the isotopes were assigned same position as they have same atomic number.

In Mendeleev’s periodic table, elements namely Fe, Co, Ni were placed together in Group VIII.

In Modern periodic table, these elements were placed under d-block elements in different groups.