orbitaloverlap

Orbital overlap is a concept in quantum chemistry that describes how much atomic orbitals on neighboring atoms occupy the same region of space. When orbitals overlap effectively, electrons can be shared between atoms, which lowers the system’s energy and stabilizes a chemical bond.

Overlaps come in several types. Sigma overlap occurs when orbitals overlap end-to-end along the bond axis, as in the overlap between two s orbitals or between an s and a p orbital. Pi overlap arises from side-by-side interaction of parallel p orbitals, forming pi bonds above and below the bond axis. Other combinations, such as s–p and p–p, can contribute to sigma or pi bonding depending on geometry. In molecular orbital theory, constructive overlap builds bonding orbitals with lower energy, while destructive overlap produces antibonding orbitals with higher energy, characterized by a node between nuclei.

The extent of overlap is governed by the overlap integral, the internuclear distance, and orbital orientation and symmetry. Maximum bonding interaction occurs at an optimal distance where wavefunctions align in phase. Hybridization combines atomic orbitals into hybrid orbitals (like sp, sp2, sp3) to maximize sigma overlap along the bond axis, while unhybridized p orbitals can provide pi overlap for multiple bonds or delocalized systems.

Applications of orbital overlap include explaining bond strengths, bond orders, and reaction mechanisms. Delocalization in conjugated systems or aromatic rings arises from extended p-orbital overlap, while in solids, repeated orbital overlap leads to band formation.