Mendeleev's Periodic Law — Prelims Strategy

Prelims Strategy

To ace NEET questions on Mendeleev's Periodic Law, a multi-faceted strategy is key. Firstly, memorize the exact statement of Mendeleev's Periodic Law: 'The properties of the elements are a periodic function of their atomic masses.

' Understand that 'atomic mass' is the fundamental basis. Secondly, create two distinct lists: 'Merits' and 'Demerits'. For merits, focus on: (1) Systematic classification, (2) Prediction of undiscovered elements (specifically remember Eka-aluminium $ightarrow$ Gallium, Eka-silicon $ightarrow$ Germanium, Eka-boron $ightarrow$ Scandium, Eka-manganese $ightarrow$ Technetium), and (3) Correction of doubtful atomic masses (e.

g., Beryllium). For demerits, focus on: (1) Position of Hydrogen, (2) Position of Isotopes (different atomic masses, same chemical properties), (3) Anomalous Pairs (e.g., Ar-K, Co-Ni, Te-I – remember these specific examples and why they were anomalous), (4) Position of Lanthanides and Actinides, and (5) Lack of explanation for the cause of periodicity.

When tackling MCQs, carefully read the question to identify if it's asking about merits or demerits. For numerical problems (though rare for this specific subtopic, conceptual numericals like atomic mass correction might appear), apply the principles of valency and group placement.

Always be wary of trap options that confuse Mendeleev's Law with the Modern Periodic Law, especially regarding atomic number vs. atomic mass.