In 1928, Linus Pauling proposed a structure for α-Keggin anions consisting of a tetrahedral central ion, [XO4]"n"−8, caged by twelve WO6 octahedra. In this proposed structure, three of the oxygen on each of the octahedra shared electrons with three neighboring octahedra. As a result, 18 oxygen atoms were used as bridging atoms between the metal atoms. The remaining oxygen atoms bonded to a proton. This structure explained many characteristics that were observed such as basicities of alkali metal salts and the hydrated form of some of the salts. However the structure could not explain the structure of dehydrated acids.