Water molecules interact strongly with ions , which are electrically-charged atoms or molecules. Dissolution of ordinary salt (NaCl) in water yields a solution containing the ions Na + and Cl – . Owing to its high polarity, the H 2 O molecules closest to the dissolved ion are strongly attached to it, forming what is known as the inner or primary hydration shell . Positively-charged ions such as Na + attract the negative (oxygen) ends of the H 2 O molecules, as shown in the diagram below. The ordered structure within the primary shell creates, through hydrogen-bonding, a region in which the surrounding waters are also somewhat ordered; this is the outer hydration shell, or cybotactic region.