Sulfur dioxide is released during the burning of sulfur-containing coal. Much of that gas is now
removed from the effluent and used in the production of sulfuric acid. The dioxides of Se and Te are
recovered from the residue after the elements have reacted with concentrated HNO 3 .
Although the boiling point of SO 2 is 75.5°C, that of SeO 2 is 340°C, and that of TeO 2 is 733°C. It
hardly needs to be stated that these data suggest a drastic difference in bonding in the molecules. In
the gas phase, the SO 2 molecule has a structure that can be represented by two resonance structures,