Redistribution of the @V06588@-shell @E01986@ throughout a molecular entity as compared with some localized models (individual atoms in their @V06588@ states, separated bonds or fragments). Different topological modes of the electron @D01583@ include:

1. ribbon @D01583@ of either π- or σ-electrons (i.e., electrons occupying respectively π- and σ-orbitals)
2. surface @D01583@ 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 @D01583@ of σ-electrons through an overlap of σ-orbitals directed inside a molecular polyhedron, as is the case in tetrahedrane.