Question #8954c

1 Answer
Jan 11, 2015

The question of how the macroscopic properties of any substance reflect its molecular properties is a huge topic that is beyond the scope of this question. However, most of the unusual macroscopic properties of water are a consequence of its tendency to form a long-range network of hydrogen bonds between the molecules.

Each water molecule has one O atom that is covalently bonded to two H atoms, plus two lone pairs of electrons that are capable of forming weaker hydrogen bonds to H atoms belonging to other water molecules. The result is a low-density tetrahedral network of water molecules that can freely exchange covalent and hydrogen bonds.

Some of the distinctive properties of water that result from this are

  • Water has an unusually high heat capacity. Water is almost universally used as a cooling agent in industry because it is cheap and because it carries a tremendous amount of heat away from engines, turbines, etc.
  • Water expands when it freezes in order to take maximum advantage of the lowered energy associated with forming a tetrahedral network of covalent and hydrogen bonds between O and H atoms.
  • Water that is a few degrees below 0 C will melt under the influence of high pressure. This is why ice skates can make ice slippery enough to glide easily (when the blades are sharp enough to form high pressure on the ice).