Question

why was mendeleev's periodic law modified?​

Answer 1

Answer:

He was unable to locate hydrogen in the periodic table. Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable. Later on, isotopes of elements were found which violated Mendeleev's periodic law.

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Answer 2

Explanation:

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1. Anomalous pairs

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.4. Separation of chemically similar elements

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.4. Separation of chemically similar elementsElements which are chemically similar such as Gold and Platinum have been placed in separate groups.

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.4. Separation of chemically similar elementsElements which are chemically similar such as Gold and Platinum have been placed in separate groups.5. Electronic arrangement

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.4. Separation of chemically similar elementsElements which are chemically similar such as Gold and Platinum have been placed in separate groups.5. Electronic arrangementIt does not explain the electronic arrangement of elements.

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.4. Separation of chemically similar elementsElements which are chemically similar such as Gold and Platinum have been placed in separate groups.5. Electronic arrangementIt does not explain the electronic arrangement of elements.6. The position of hydrogen

1. Anomalous pairsThe following pairs of elements did not follow Mendeleev’s Principles:Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.4. Separation of chemically similar elementsElements which are chemically similar such as Gold and Platinum have been placed in separate groups.5. Electronic arrangementIt does not explain the electronic arrangement of elements.6. The position of hydrogenHydrogen was not given a fixed position. 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.