Conditions for Linear Combination of Atomic Orbitals
To successfully form stable molecular orbitals, the combining atomic wave structures must adhere strictly to the following parameters set by the LCAO approximation method:
The mixing atomic orbitals must possess identical or nearly matching internal energy parameters. For instance, a 2p orbital belonging to one atom can natively blend with a equivalent 2p shell of another atom; however, a 1s orbital cannot effectively merge with a 2p orbital due to their substantial and incompatible energy variations.
Interacting atomic centers must match structural symmetries relative to the fundamental molecular link path to provide structural alignment. While isolated 2p clouds hold uniform baseline energy profiles, a 2pz cloud can only combine cleanly with another 2pz shell. The 2px and 2py orbitals do not combine with a 2pz configuration because their primary orientation lines are perpendicular. Conventionally, the z-axis is fixed as the reference molecular axis of symmetry.
Atomic paths will form robust molecular orbitals if and only if the directional configurations allow proper spatial intersection. The broader the overlap volume achieved by these constituent atomic orbitals, the higher the overall electronic density accumulated between the twin nuclei, leading to a much more stable covalent bond configuration.
Which of the following combinations is not allowed in the LCAO method for the formation of a molecular orbital? (Consider the Z-axis as the molecular axis)
See Hint
Correct Answer: A
The s and px orbitals do not possess the proper spatial orientation or matching alignment parameters relative to the shared z-axis. As a result, they experience net zero overlap, meaning no molecular orbital can be formed.