MP Board · Class 10 · Science · Periodic Classification of ElementsCompare Mendeleev's Periodic Table with the Modern Periodic Table. Highlight the basis of classification, anomalies resolved, and limitations that were corrected.

Basis of Classification

• Mendeleev's Periodic Table: Mendeleev classified elements on the basis of their fundamental property, atomic mass, and chemical reactivity (specifically their oxides and hydrides).
• Modern Periodic Table: Henry Moseley modified it by using atomic number as the basis of classification, which is a more fundamental property representing the number of protons in the nucleus.

Anomalies and Limitations Addressed

• Position of Isotopes: In Mendeleev's table, isotopes posed a serious problem because they have different atomic masses but the same chemical properties. The Modern Periodic Table resolved this because isotopes have the same atomic number and are placed in the same slot.
• Anomalous Pairs of Elements: Mendeleev had to place certain elements with higher atomic masses before elements with lower atomic masses (e.g., Cobalt and Nickel) to match their chemical properties. The Modern Periodic Table eliminated this anomaly as elements are arranged strictly by increasing atomic numbers.
• Position of Hydrogen: The position of hydrogen was uncertain in Mendeleev's table as it resembles both alkali metals and halogens. In the Modern Periodic Table, hydrogen is placed in Group 1 based on its electronic configuration, though its position remains uniquely discussed.
• Predictive Power: While Mendeleev successfully left gaps for undiscovered elements (like Eka-boron, Eka-aluminium, and Eka-silicon) and predicted their properties, the Modern Periodic Table provides a more systematic framework based on electronic configurations explaining periodicity completely.