Why do salts such as NaCl dissolve in water? Polar solvents, such as wa- ter, weaken the attractive forces between oppositely charged ions (such as Na ⫹ and Cl ⫺ ) and can therefore hold the ions apart. (In nonpolar solvents, ions of opposite charge attract each other so strongly that they coalesce to form a solid salt.) An ion immersed in a polar solvent such as water attracts the op- positely charged ends of the solvent dipoles (Fig. 2-6). The ion is thereby sur- rounded by one or more concentric shells of oriented solvent molecules. Such ions are said to be solvated or, when water is the solvent, to be hydrated.