Heteronuclear Diatomics and Polarity in Orbital Terms
When the two atoms differ, their orbitals no longer sit at the same energy, so the shared orbitals lean towards one atom. Bond polarity stops being an arrow on a bond and becomes an unequal contribution to a molecular orbital.
What a learner can do afterwards
- Places the atomic levels of two different atoms at different energies and explains which one dominates the bonding orbital
- Links the size of the energy mismatch to the degree of ionic character
- Builds the diagram for carbon monoxide and identifies the orbital that makes it a ligand
- Explains why two orbitals must be close in both energy and symmetry to interact usefully
1 · Read
When the two atoms differ, their atomic orbitals start at different energies, and that offset reshapes every molecular orbital. The bonding combination takes after the lower energy partner, so its electrons pile up on the more electronegative atom. The antibonding combination takes after the higher partner instead. Sketch the uneven ladder first, with one atomic set drawn lower, and polarity becomes visible before any numbers.
The bigger the energy mismatch, the more one sided the sharing becomes, until the bond reads as essentially ionic. Read every bond as a point on a sliding scale set by the gap: small gaps share evenly, middle gaps go polar covalent, large gaps go ionic. Molecular polarity then adds the bond dipoles as vectors, so carbon dioxide stays nonpolar because symmetry cancels its vectors exactly.
Carbon monoxide is the showcase. Oxygen brings the lower atomic orbitals, so the bonding orbitals concentrate on oxygen while the highest occupied orbital ends up mostly carbon in character. That carbon centred lone pair donates to metals, which is why carbon monoxide binds through carbon rather than oxygen. Useful overlap always demands two things at once: energies close together and symmetries that match.
Symmetry still rules over eagerness. Orbitals of mismatched symmetry cannot combine no matter how close their energies sit, and such pairs stay nearly nonbonding on one atom. Check symmetry before you sketch any heteronuclear ladder.
Uneven ladders lean, big gaps go ionic, and overlap demands energy plus symmetry.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.