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Water’s Hydrogen Bond Strength: Martin Chaplin

Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for lifegiving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy. These hydrogen bonds are roughly tetrahedrally arranged such that when strongly formed the local clustering expands, decreasing the density. Such low density structuring naturally occurs at low and supercooled temperatures and gives rise to many physical and. | Water s Hydrogen Bond Strength Martin Chaplin London South Bank University Borough Road London SE1 0AA UK Email martin.chaplin@lsbu.ac.uk Abstract. Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for life-giving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy. These hydrogen bonds are roughly tetrahedrally arranged such that when strongly formed the local clustering expands decreasing the density. Such low density structuring naturally occurs at low and supercooled temperatures and gives rise to many physical and chemical properties that evidence the particular uniqueness of liquid water. If aqueous hydrogen bonds were actually somewhat stronger then water would behave similar to a glass whereas if they were weaker then water would be a gas and only exist as a liquid at sub-zero temperatures. The quantitative and qualitative consequences of strengthening or weakening of the hydrogen bond in water are conside red in this paper. It is found that if the hydrogen bond strength was slightly different from its natural value then there may be considerable consequences for life. At the extremes water would not be liquid on the surface of Earth at its average temperature if the hydrogen bonds were 7 stronger or 29 weaker. The temperature of maximum density naturally occurring at about 4 C would disappear if the hydrogen bonds were just 2 weaker. Major consequences for life are found if the hydrogen bonds did not have their natural strength. Even very slight strengthening of the hydrogen bonds may have substantial effects on normal metabolism. Water ionization becomes much less evident if the hydrogen bonds are .