Periodic Classification of Elements — Science STD 10 — Question
CBSE BoardEnglish MediumSTD 10SciencePeriodic Classification of Elements2 Marks
Question
Describe two anomalies of Mendeleev’s periodic classification of elements.
✓
Answer
Anomalies of Mendeleev’s classification of elements:
The position of isotopes could not be explained: If the elements are arranged according to atomic masses, the isotopes should be placed in different groups of the periodic table. But, the isotopes were not given separate places in Mendeleev’s periodic table. They were placed at the same place in the table. This placing of the isotopes at same place could not be explained by Mendeleev’s periodic law.
Wrong order of atomic masses of some elements could not be explained: In Mendeleev’s periodic table, when certain elements were put in their correct group on the basis of their chemical properties, it was found that the element with higher atomic mass comes first and the element with lower atomic mass comes later. Mendeleev’s periodic law could not explain this abnormal situation of wrong order of atomic masses.
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