The Pennycuik-Starmer Uniformist Model of Water

THE PENNYCUIK-STARMER UNIFORMIST MODEL OF WATER

By
Philip H. Starmer

Email: st9m6@windstream.net

In a study of the swelling of nitrile rubbers (copolymers of butadiene and acrylonitrile) by various liquids it was found (1, 2, 3). that the swelling was related to the acrylonitrile level in the rubber by a bell-shaped curve and that the maximum value of the curve was, in most cases, inversely related to the molar volume (molecular weight divided by density) of the liquid. The exceptions were the alcohols butanol and pentanol which behaved as though they had a molar volume of six times the calculated value. This led to the associated structure of alcohols as proposed by Pauling (4).in which six alcohol molecules form a puckered ring structure with dangling alkyl groups.

The question arises, what happens if the alkyl groups are replaced by hydrogen? Is this the structure of water? This uniformist model of a cyclic structure of a puckered ring of six H2O molecules was proposed by Pennycuik (5) in 1928 but was not adopted because of difficulty of explaining, when ice melts, why some hydrogen bonds were broken and others stay intact. The Pennycuik model can be explained by the proposal(6) that the.two hydrogen bonds that an oxygen atom can form are not equal, with one being stronger than the other. This concept is supported by the work of Jean and Volatron (7) who observed that the two lone pair electron groups on an oxygen atom are not of equal energy. It follows that two types of hydrogen bonds exist in ice, the weak ones break when ice melts and the strong bonds persist in water and break when water boils. Thus, water vapor is H2O, water is (H2O)6 and ice is [(H2O)6]n. Clary(8), using computer simulations, predicted that the basic structure of water is a hexamer. It was estimated (6) that the weak H-bond has a strength of 5.9 kJ per mol while the strong H-bond has a strength of 37.7 kJ per mol. Note that the average is close to the value of 21 kJ per mol estimated by Pauling (4) for the strength of the H-bond in water. The value for the strong H-bond will, perhaps, explain why water has a higher critical temperature (374.15 deg.C) that that of hydrogen fluoride (230.0 deg.C). It had been previously thought that the H-bonds in hydrogen fluoride (28.1 kJ per mol) were stronger than those in water.(9) The strong hydrogen bonds correspond to the hydrogen bonds in alcohols. The weak H-bonds are a possible reason for the plasticity of ice in glaciers. This behavior is analogous to the plastic behavior of zinc oxide-carboxyl polymers where the plasticity arises due to the breakage and reformation of labile cross-links formed through zinc oxide-carboxyl group interactions (10).These ionic bonds are weaker than the covalent bonds which form the backbone of the polymer and may be considered analogous to the weaker H-bonds in ice.

Using simple high school level mathematics, an equation was derived for the volume of a hexagonal cell containing a puckered ring of six H2O molecules(11). The volume is related to the O – O – O angle and the O – O distance. A little calculus shows that the maximum volume and, thus, the minimum density occurs when the O – O – O angle equals the tetrahedral angle, 109 deg 28’, the situation that occurs in ice.(11).. The graph shows that the increase in density on melting can be easily explained by the O--O--O angle increasing to almost 120 degrees in water. This further suggests that the maximum density (at about 4deg C) occurs when the angle is 120 degrees at which point the structure is flat. It is postulated, that at this temperature, the structure changes from the chair form (per cyclohexane) at lower temperatures to the boat form at higher temperatures. Does this mean that ships float on the boat form of water?

The Pennycuik-Starmer Uniformist Model of Water has explanations for:
1) the melting point of ice – weak H-bonds
2) the plasticity of ice in glaciers – weak H-bonds
3) the increase of density on melting – O-O-O angle increase from the tetrahedral angle in ice to nearly 120 degrees in water at 0 deg. C
4) the maximum density at 4 deg.C - O-O-O angle equal to 120 deg
5) the boiling point of the liquid – strong H-bonds
6) the high critical temperature – strong H-bonds
7) viscosity similar to that of cyclohexane- cyclic structure & the same molar volumes (108).
8) good solvent – formation of H-bonds with non-cyclic hydrogen atoms

Barium sulfate is extremely insoluble in water and is non-toxic. It is used as the barium meal in medical applications. Barium chloride, on the other hand, is very soluble in water and is highly toxic. A possible explanation is that water forms hydrogen bonds with the chloride and not with the sulfate. Further, water molecules encapsulate the chloride molecule in such a way that other water molecules only see water and not the chloride so it is dissolved.

References:
1) P.H.Starmer J Elastomers and Plastics, Vol. 25, 59, 1993
2) P.H.Starmer, ibid Vol. 25, 120, 1993
3) P.H.Starmer, ibid Vol 25, 188, 1993
4) L.Pauling, The Nature of the chemical bond, Cornel Un.Press,1960
5) S.W.Pennycuik, J. Phys. Chem, 32,1681, 1928
6) P.H.Starmer, Indian J. Chem. 37A, 1002, 1998
7) Jean J., & Volatron F. An introduction to molecular orbitals, (translated by J Burden) Oxford University Press, New York 1993
8) D.Clary, The Economist, March 21, 1998
9) H.S.Frank, Science, 169, 3946, 635, 1970
10) P.H.Starmer, Plast. Rub. Process Appl., 9, 209 1988.
11) P.H.Starmer, www.structureofice.blogspot.com 2008

Philip H. Starmer is a retired BF Goodrich Scientist. He lives and works in Charlotte, NC.

Other Articles by Philip Starmer:

-The Hexagonal Cell Structure of Ice-I

-Prime Numbers and Goldbach's Conjecture