Phases of Matter IX: The Wonder of Water 2

Crossposted at Dailykos.com

Hydrogen bonds are not very strong, but they are common. Looking it from an energetic standpoint, covalent bonds (the pure sharing of electrons, like in diatomic oxygen, for example), then ionic bonds, like in salt, are stronger. But there are lots of hydrogen bonds, and numbers have power. The only other that is so diffuse, and thus so powerful, are metallic bonds. I have covered all of those in previous diaries.

A hydrogen bond forms when a hydrogen atom (the smallest and lightest) is bonded with either nitrogen, oxygen, or fluorine. From a zero point approximation, a hydrogen bond is a strong dipole-dipole bond, but they are much more important and quite different.

Whilst we have not explained it well yet with models, it is a fact that it exists. Here are some of the empirical reasons:

Water, with a molecular mass of 18, should be a gas even at minus 100 degrees C. Hydrogen sulfide is a gas, the next more heavier relative. So are all of the other hydrogen chalcogens, except for water.

The hydrogen bond is certainly very much a dipolar one, but because of the low mass of a hydrogen nucleus, the Heisenberg Uncertainty Principle comes to bear. That means that it is impossible to determine both the position and the momentum of any given particle, and the lighter it is, the harder it is to determine it. Other than electrons, hydrogen is the lightest.

Many physicists might disagree with my statement, but not the essence of it. Because of the Uncertainty Principle, it is not possible to locate a hydrogen atom very well, and the uncertainty of that has entropic ramifications. That is the marriage of the macromatic (thermodynamics) and the microscopic (quantum mechanical) realities of our universe.

Here are three real world examples.

Water should boil around 20 degrees K, because of its molecular mass. But it boils at 373 degrees K, because of mass effects of the hydrogen bonds.

Ice should be more dense than water at the freezing point. But it is not. It is around 11% more in volume, because of the hydrogen bonding of the constituent water molecules. They organize, because of those bonds, into a less dense structure.

Finally, let us think about ironing clothes. Cotton clothes, in particular, are wont to wrinkle. That is because cotton has a surface full of OH groups, that hydrogen bond with other OH groups in a random fashion. Now take the iron, and you apply heat to break most if not all of the random ones, and the weight of the metal presses the cloth together.

Then is cools down, after being pressed, and presto! New, regular hydrogen bonds form, making crisp flat stretches and tight folds. New, better hydrogen bonds are responsible for your nicely ironed clothes.

Oh, one more thing. Hair is similar, since it hydrogen bonds too. Dry days, not much water, and the hair is straight. Very humid days break the bonds and allow hair to bond with its own hydrogen bond acceptors and,or receptors.

I hope that this makes some sense. It is a difficult subject, and not many models are available to explain it completely. I will hang around a while to respond to comments. Warmest regards, Doc

Tags: Hydrogen bond, Matter, Quatum Mechanics, Teaching, Water