Molecular Orbital Theory — Prelims Strategy

Prelims Strategy

To excel in NEET questions on Molecular Orbital Theory, a systematic approach is crucial. First, thoroughly understand the two different MO energy level diagrams: one for elements up to nitrogen (including $B_2, C_2, N_2$) where s-p mixing occurs ($pi 2p$ before $sigma 2p_z$), and another for oxygen and fluorine (including $O_2, F_2$) where s-p mixing is negligible ($sigma 2p_z$ before $pi 2p$).

Memorize these orders. Second, practice calculating the total number of electrons for various diatomic molecules and ions, paying close attention to charges. Third, meticulously fill electrons into the MOs following the Aufbau principle, Pauli exclusion principle, and Hund's rule.

Fourth, calculate the bond order using the formula $BO = \frac{1}{2}(N_b - N_a)$. Fifth, identify unpaired electrons to determine magnetic properties (paramagnetic if unpaired, diamagnetic if all paired).

Finally, remember the relationships: higher bond order means greater stability, shorter bond length, and higher bond dissociation energy. For conceptual questions, focus on the fundamental differences between MOT and VBT, especially regarding electron delocalization and magnetic properties.

Be wary of trap options that misapply the s-p mixing rule or incorrectly count electrons.