Uranium oxygen bond order

Taken together, these observations signify a role for both the 5/and 6d shells in the bonding, and show that all twelve electrons in the valence shell participate. This description gives each uranium-oxygen linkage a formal bond order of three. From this point of view it is the availability of metal valence orbitals of both parities which make the actinyl bond so strikingly different from metal-oxo bonds in the transition series, where only the metal d-shell plays a dominant role. 

Fig. 13 is a drawing of electron-domain models of some Group VI hexafluorides. Open circles represent the electron-pairs of four of the six bonds to fluorine atoms in a Lewis, single-bond formulation of these molecules. Solid circles represent the atomic cores of oxygen, sulfur, selenium, tellurium, tungsten, and uranium (core radii, in hundreths of A, 9, 29, 42, 56, 62, and 80 2>, respectively). These hexafluorides are, in order, non-existent, extra-ordinarily unreactive, hydrolyzed slowly, hydrolyzed completely at room temperature in 24 hours, hydrolyzed readily, and hydrolyzed very rapidly. 

---