The Anomaly of Beryllium

The crystal structures of these solid carbonates are such that it cannot be said that one particular metal ion belongs to one particular carbonate ion nevertheless, a portion of the structure may be represented schematically  

As with lithium, many properties of beryllium stand distinctly apart from those of its congeners. Again, the tiny size of the beryllium ion is responsible for the peculiarities. If we arbitrarily call the volume of the magnesium ion 1.0 unit, the volumes of the calcium, strontium, and barium ions become, respectively, about 3, 5, and 8 units however, the volume of the beryllium ion is, on the same scale, only 1/8 unit. Since the oxide is amphoteric, one would expect many of the salts of Be+2 to be extensively hydrolyzed in water (as is the case with the salts of Al8+, Zn2+, and Cr8+). The acidity of beryllium-containing solutions is also increased by polymerization of the beryllium-containing ions  

Beryllium far surpasses its congeners in its ability to form complexes. Besides the stable BeF ion, beryllium forms many complexes having 

As seen, both of these complex ions have five-membered rings of atoms they are called chelates (Chap. 22). The four oxygen atoms bound to the beryllium are actually not in the same plane rather, they are at the corners of a regular tetrahedron with the beryllium ion at the center. 

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