Chemistry · Chemical Bonding · NEET
NCERT lists exactly three. (1) The combining atomic orbitals must have the same or nearly the same energy. (2) They must have the same symmetry about the molecular axis (the z-axis by convention). (3) They must overlap to the maximum possible extent. All three must hold together. If any one fails, no useful molecular orbital forms.
Because their energies are too different. The energy of the 2s orbital is much higher than that of 1s. The energy condition says orbitals must be at the same or nearly the same energy level. Since 1s and 2s energies do not match, they cannot combine (except when the two atoms are very different, which is a special case).
Because of symmetry. By convention the z-axis is the molecular (bond) axis. The 2pz orbital points along this axis and has one type of symmetry about it. The 2px and 2py orbitals point sideways and have a different symmetry about the z-axis. Orbitals combine only if their symmetry about the bond axis matches, so 2pz pairs only with 2pz.
Take the line joining the two nuclei as the z-axis (the molecular axis). Each orbital has a certain shape and sign pattern around this axis. Two orbitals have the same symmetry if their lobes are arranged the same way relative to that axis, so a positive lobe meets a positive lobe. If one orbital is symmetric and the other is not (like 2pz vs 2px), the overlap cancels out and no bonding orbital forms.
No. Same energy alone is not enough. NCERT clearly states that orbitals with the same or nearly the same energy will still NOT combine if they do not have the same symmetry. So you need same energy AND same symmetry AND maximum overlap, all three together.
Greater overlap means greater electron density between the two nuclei. More electron density between the nuclei means a stronger bond and a more stable bonding molecular orbital. That is why the third condition asks the orbitals to overlap to the maximum extent possible.
Which one of the following statements is incorrect related to Molecular Orbital Theory?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. In molecular orbital theory the atomic orbitals come from the two (or more) atoms that are bonding. For example, a 1s orbital of one atom combines with a 1s orbital of the other atom.
Two. NCERT states the number of molecular orbitals formed equals the number of combining atomic orbitals. Two atomic orbitals give one bonding molecular orbital (lower energy) and one antibonding molecular orbital (higher energy).
By convention the z-axis is taken as the molecular axis, meaning the line joining the two nuclei is the z-axis. Symmetry is always judged about this axis.
Yes. NTA regularly asks statement-based questions on MO theory (2019, 2023, 2026). Knowing these three conditions and the symmetry rule (2pz-2pz vs 2px-2px) directly helps you spot the incorrect statement quickly.
