Valence Bond Theory — Prelims Strategy

Prelims Strategy

To excel in VBT questions for NEET, a systematic approach is essential. First, always determine the oxidation state of the central metal ion accurately, as this dictates its d-electron count. Second, write down the electronic configuration of the metal ion.

Third, identify the coordination number and, critically, the nature of the ligands (strong field vs. weak field). Remember the common strong field ligands (CN$^-$, CO, NH$_3$, en) and weak field ligands (H$_2$O, F$^-$, Cl$^-$, Br$^-$, I$^-$).

This classification determines whether electron pairing occurs in the d-orbitals. For numerical problems involving magnetic moment, count the unpaired electrons 'n' carefully and use the formula $\mu = \sqrt{n(n+2)}$ BM.

For conceptual questions, be mindful of VBT's limitations, especially its inability to explain color or quantitative stability. Practice with various examples covering different coordination numbers (4 and 6) and d-electron configurations.

Pay special attention to $d^8$ and $d^9$ configurations for square planar complexes, as they can be tricky. Always double-check your electron count and pairing decisions.