phosphorous (image of box/arrow diagrams of electron configurations). 1s2 2s2 2p3 v. 1s2 2s2 2p6 3s2 3p3 - phosphorous has vacant 3d orbitals that can be used in bonding - 'expanded valence shell.' ...

However, oxides with transition metals that straddle the subtle boundary between covalent, ionic and metallic bonding show copious ... clouds of electrons, the orbitals, move around and interact ...