Redistribution of the valence-shell electron density throughout a molecular entity as compared with some localized models (individual atoms in their valence states, separated bonds or fragments). Different topological modes of the electron delocalization include:

1. ribbon delocalization of either π- or σ-electrons (i.e., electrons occupying respectively π- and σ-orbitals)
2. surface delocalization of σ-electrons occurring through an overlap of radially oriented σ-orbitals of a cyclic molecule, as is the case of cyclopropane; and
3. volume delocalization of σ-electrons through an overlap of σ-orbitals directed inside a molecular polyhedron, as is the case in tetrahedrane.