<P> When an ionic or polar compound enters water, it is surrounded by water molecules (hydration). The relatively small size of water molecules (~ 3 angstroms) allows many water molecules to surround one molecule of solute . The partially negative dipole ends of the water are attracted to positively charged components of the solute, and vice versa for the positive dipole ends . </P> <P> In general, ionic and polar substances such as acids, alcohols, and salts are relatively soluble in water, and non-polar substances such as fats and oils are not . Non-polar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in van der Waals interactions with non-polar molecules . </P> <P> An example of an ionic solute is table salt; the sodium chloride, NaCl, separates into Na + cations and Cl − anions, each being surrounded by water molecules . The ions are then easily transported away from their crystalline lattice into solution . An example of a nonionic solute is table sugar . The water dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution . </P> <P> The quantum tunneling dynamics in water was reported as early as 1992 . At that time it was known that there are motions which destroy and regenerate the weak hydrogen bond by internal rotations of the substituent water monomers . On 18 March 2016, it was reported that the hydrogen bond can be broken by quantum tunneling in the water hexamer . Unlike previously reported tunneling motions in water, this involved the concerted breaking of two hydrogen bonds . Later in the same year, the discovery of the quantum tunneling of water molecules was reported . </P>

What describes the structure of a water molecule h2o