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Limitation of mendeleevs. How removed in modern p.t |
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Answer» Limitation of Mendeleev periodic table.(i) Position of hydrogen: Hydrogen is placed in Group IA. However, it actually resembles the elements of Group-IA (alkali metals ) as well as the elements of Group VII-A (halogens ). Thus, the position of hydrogen in the periodic table is not clear.(ii) Position of isotopes: On the basis of atomic weight , various isotopes of the same elements should be assigned different places in the periodic table. Mendeleev could not provide separate places for isotopes.(iii) Position of lanthanides and actinides: Fourteen elements following Lanthanum(known as lanthanides or rare earths) and the fourteen elements following Actinium (known as actinides or transuranic elements ) have not been provided separate and proper places in the Mendellev\'s table, rather they have been placed in two rows at the bottom of the table.(iv) Dissimilar elements placed together: Noble metals like Cu, Ag and Au are placed along with chemically dissimilar alkali metals in Group I . Similarly, Mn possessing very few similarities with halogens have been placed in VII group.(v) Similar elements separated: In Mendeleev\'s periodic table, certain chemically similar elements such as copper and mercury ; gold and platinum have been placed in different groups.Mendeleev was unable to give fixed position to hydrogen and isotopes in the periodic table. In Mendeleev’s periodic table, the increasing manner of atomic mass of the elements is not always regular from one to its next. It was believed that a more fundamental property than atomic mass could explain periodic properties in a better manner.It was Henry Moseley who demonstrated that atomic number of an element could explain periodic properties in a better way than atomic mass of an element and arranged the elements in increasing order of their atomic numbers. Then it was found that the various anomalies of Mendeleev’s periodic table were removed by the modern periodic table. They cannot assign the position of hydrogen.hydrogen resembles the alkali metal as well as the helogens.he can not assign the position of iso topes. |
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