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How does an antibonding molecular orbital differ from a bonding molecular orbital?
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covalent bond
In polar covalent bonds, such as that between hydrogen and oxygen atoms, the electrons are not transferred from one atom to the other as they are in an ionic bond. Instead, some outer electrons merely spend more time in the vicinity of the other atom. The effect of this orbital distortion is to induce regional net charges that hold the atoms together, such as in water molecules.
In molecular orbital theory, bonding and antibonding orbitals are distinguished by how atomic orbitals interfere and their resulting effect on electron energy and distribution.1
- Bonding Orbitals: These are formed when atomic orbitals interfere constructively, resulting in an enhanced amplitude of electron density between the nuclei. Because electrons in these orbitals are concentrated in the internuclear region, their energy is lower than when they are confined to isolated atoms, which promotes molecular stability.1
- Antibonding Orbitals: These are formed through destructive interference, which creates a nodal plane—a region of zero electron amplitude—between the nuclei. Electrons occupying these orbitals are excluded from the internuclear region, resulting in an energy level higher than that of the individual atomic orbitals. Consequently, the occupation of antibonding orbitals decreases the stability of a molecule.1
In summary, while bonding orbitals accumulate electron density between nuclei to lower energy, antibonding orbitals create a node that pushes electron density away, raising the system's energy.1