Sulfur mean bond energy

Fig. 3 Mean bond energies of the sulfur homocycles S6...S23 in liquid sulfur relative to Sg. AE is the difference in mean bond energies between Sg and the particular ring (in kj mok ) [93]...

The molecular structure of sulfur dioxide is angular, while the structure of the trioxide is trigonal planar. See Fig. 20.2. It is noteworthy that the bond distances in SO2 and SO3 are 5 or 6 pm shorter than in the monoxide, while the mean bond energies in SO2 and SO3 are respectively 3% greater and 9% smaller than the dissociation energy of the monoxide. These observations indicate that the SO bonds in these molecules are best described as double. 

The electrons in a 7t-bond are further from the nuclei than the electrons of a o-bond, and therefore at a higher energy level, less stable, and form a weaker bond. This is important because less stability means Ji-bonds are more reactive. Third row elements form weaker 7c-bonds than second row elements. Double and triple bonds are rare for all atoms except carbon, nitrogen, oxygen, and sulfur. 

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