MP Board · Class 10 · Science · Periodic Classification of ElementsExplain Mendeleev's Periodic Law and its contributions to the classification of elements. Also discuss the major anomalies or limitations of Mendeleev's Periodic Table.

Introduction to Mendeleev's Periodic Law\nDmitri Mendeleev, a Russian chemist, formulated the Periodic Law, which states that 'the properties of elements are the periodic function of their atomic masses.' Based on this law, he arranged the 63 known elements at that time in order of increasing atomic masses, grouping elements with similar chemical properties together into a tabular arrangement known as Mendeleev's Periodic Table.

Major Contributions and Merits

• Systematic Study of Elements: Mendeleev's periodic table simplified and organized the study of a vast number of elements and their numerous compounds into manageable groups.
• Prediction of New Elements: With remarkable foresight, Mendeleev left vacant gaps in his periodic table for elements that had not been discovered at that time. He boldly predicted the existence and properties of these undiscovered elements, naming them eka-boron, eka-aluminium, and eka-silicon (which were later discovered as Scandium, Gallium, and Germanium, respectively).
• Correction of Atomic Masses: Mendeleev corrected the atomic masses of certain elements based on their proper placement in the periodic table, aligning their properties with the correct group.

Anomalies and Limitations

• Position of Isotopes: Since isotopes of an element have different atomic masses but identical chemical properties, they could not be given separate places in Mendeleev's table, violating the core principle.
• Anomalous Pairs of Elements: In certain instances, elements with higher atomic masses were placed before elements with lower atomic masses to group similar elements together (e.g., Cobalt with an atomic mass of 58.9 was placed before Nickel with 58.7).
• Position of Hydrogen: Hydrogen resembles both alkali metals (Group 1) and halogens (Group 17), making it difficult to assign a fixed, unambiguous position to hydrogen in the periodic table.
• Cause of Periodicity: The periodic table failed to explain the fundamental reason behind why elements exhibit periodicity at regular intervals.