In chemistry, ice rules are basic principles that govern arrangement of
atoms in water
ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
. They are also known as Bernal–Fowler rules, after British physicists
John Desmond Bernal and
Ralph H. Fowler
Sir Ralph Howard Fowler (17 January 1889 – 28 July 1944) was a British physicist and astronomer.
Education
Fowler was born at Roydon, Essex, on 17 January 1889 to Howard Fowler, from Burnham, Somerset, and Frances Eva, daughter of George De ...
who first described them in 1933.
The rules state each
oxygen is
covalently bonded
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
to two
hydrogen atoms, and that the oxygen atom in each water molecule forms two hydrogen bonds with other water molecules, so that there is precisely one hydrogen between each pair of oxygen atoms.
In other words, in ordinary
Ih ice, every oxygen is bonded to the total of four hydrogens, two of these bonds are strong and two of them are much weaker. Every hydrogen is bonded to two oxygens, strongly to one and weakly to the other. The resulting configuration is geometrically a periodic lattice. The distribution of bonds on this lattice is represented by a directed-graph (arrows) and can be either ordered or disordered. In 1935,
Linus Pauling used the ice rules to calculate the
residual entropy (zero temperature entropy) of ice I
h. For this (and other) reasons the rules are sometimes mis-attributed and referred to as "Pauling's ice rules" (not to be confused with
Pauling's rules
Pauling's rules are five rules published by Linus Pauling in 1929 for predicting and rationalizing the crystal structures of ionic compounds.
First rule: the radius ratio rule
For typical ionic solids, the cations are smaller than the anion ...
for ionic crystals).
A nice figure of the resulting structure can be found in Hamann.
See also
*
Ice-type model
*
Bjerrum defect
References
External links
* Bernal–Fowler rules in Glossary of Meteorology
* Exposition by Chris Wilson and Brett Marmo
*
{{DEFAULTSORT:Ice Rules
Water ice