Even the noble gases are not totally immune from attack by fluorine. The most electronegative of all the elements, fluorine, can form covalent bonds with the least electronegative of all the noble gases, xenon, by sharing some of xenon's eight outer-shell electrons. Two F atoms can divide and share one of xenon's lone electron pairs between them to form , which has ten electrons around the central Xe: two bonding pairs to the F atoms and three lone pairs. VSEPR theory predicts a linear F-Xe-F structure for this molecule, as shown at the top of the opposite page, with the strongly repelling lone pairs 120° apart in a plane perpendicular to the molecular axis. Two more F atoms can share a second xenon lone pair to produce with the xenon atom surrounded by four bonding pairs and two lone pairs. VSEPR theory predicts that this molecule will be most stable if the strongly repelling lone pairs are as far apart as possible, at opposite vertices of an octahedron, and the four F atoms lie in an equatorial plane, as drawn on the opposite page. A third xenon lone pair is shared by two more F atoms in , with the xenon atom surrounded by seven electron pairs in a distorted octahedron. A few xenon and krypton compounds with the strongly electronegative oxygen atom also are known.

With the exception of compounds formed with , Cul, and most of the halide salts are water-soluble. Ocean water essentially is a dilute solution of NaCl, , KCl, and in the ratios of 50:6:1:1, with small amounts of other salts.