Metallic bond

The traditional picture of the metallic bond was developed soon after the discovery of the electron. In this picture the valence electrons were viewed as an electron-gas permeating the crystal lattice structre of the metal atoms. The cohesive forces holding the metal together could be qualitatively seen as resulting from the electrostatic interaction of the positively charged metal atom cores with the negatively charged electron-gas.

With the development of quantum mechanics this picture has changed significantly. Quantum mechanically covalent bonding can be described by constructing molecular orbitals from a linear combination of atomic orbitals (LCAO theory). For some molecules, such as benzene, which contain resonance in an extended conjugated system some of the molecular orbitals