Solvents differ greatly in their ability to extract compounds of metals from aqueous solution. For example, uranyl nitrate is strongly extracted by diethyl ether, hexone, TBP, and many other oxygenated organic solvents, but it is not extracted at all by benzene, kerosene, or other

hydrocarbons, in the absence of complexing agents. Extractability of a salt by an organic solvent apparently requires that an uncharged coordination complex be formed between the solvent and the salt. As discussed in Sec. 4.2, this is possible when the solvent contains oxygen, nitrogen, or other electron-donor elements and when the metal of the salt is one of the transition elements with unfilled inner electron orbits capable of sharing electrons with the solvent molecules. Such compounds are not formed with saturated hydrocarbon solvents.