This structure is isoelectronic with (SiO 3 ) 36 and (PO 3 ) 33 . Gaseous SO 3 has a trigonal planar struc-ture that has several contributing resonance structures. When the structure is drawn with only one
double bond, the sulfur atom has a 2 formal charge that is relieved by structures having two
double bonds. Therefore, multiple bonding is extensive.