Why water is so weird

By Daniel Collins 15/03/2010

I judged a book by its cover. There was this blue, amorphous blob in the throes of metamorphosis – yet frozen in time. The heading above it read: “The strangest liquid: Why water is so weird”.

It was the Feb 6 2010 edition of New Scientist, which I spied when buying the Jan-Fen 2010 edition of New Zealand Geographic. I had that consumeristic impulse. I bought it. A month later, when I got round to reading the article, I was not disappointed.

The article told the story of Anders Nilsson of Stanford University and Lars Pettersson of Stockholm University in their efforts to explain why water is indeed so weird.

What is common knowledge is that ice floats and water freezes first at the top. This is because water is the densest at 4°C. Very few other liquids behave this way – molten silica seems to be another. But wait, there’s more! Unlike most other liquids water becomes less viscous at higher temperatures, not more. Water has an uncannily high specific heat capacity, which rises both above and below 35°C whereas others have a single trend.

But, the child in us all asks, why?

Well, our heroes of the story, Nilsson and Pettersson, were using X-ray absorption spectroscopy to study the structure of an amino acid, way back 10 years ago. They realised that the water containing the amino acid was more interesting (quelle surprise!), and shifted their gaze to H2O.

Over the course of many more x-rays and several papers, they arrived at a theory to explain all of water’s weirdness: water molecules are capable of stacking themselves in not one but two configurations. One an ordered tetrahedral lattice and one a mixed up hodge-podge. It is the building and breaking of these configurations that ultimately leads, so the heroes say, to water’s wonderful properties.

This being science, though, more research is needed. There are sceptics. There are nay-sayers. There are applications like cheaper desalinisation. And there are children in us all who will continue to ask: But why?

0 Responses to “Why water is so weird”

  • It was a fantastic article…I certainly hadn’t realised quite how strange some of its properties are…

  • I haven’t read the article, but I’ve had fun learning how these properties contribute to the conditions required for life. For example, the high specific heat means that if you build a large animal out of water, thermal control is much more tractable, which means warm-blooded animals are not so far-fetched! Or that if water didn’t expand below 4C (notably when forming ice), there’s a huge range of possible climates in which ice would form on the bottoms of lakes and oceans and never melt. The fact that ice floats is crucial to having lots of it available. How would erosion be different if water had a much different density (or, again, didn’t expand when it froze)? If it weren’t such a good solvent? If it were made from less common atoms? Etc…

  • Aye, the idiosyncrasies of water also affect erosion. The expansion of water below 4°C is great for wedging apart cracks in rocks. Glacial landforms can be attributed to the strength of ice, which I assume derives from its tetrahedral packing, in combination with the topographic bias in where precipitation falls and accumulates. If memory serves me well, the dissociation of water into H+ can contribute to weakening of certain soils, as larger +ve ions are replaced. Plus, anything much less dense probably wouldn’t be able to move sediment in rivers as easily.

    That said, if a hydrological cycle with some other molecule existed – it would need a different atmos make-up and different gravity and insolation – you’d still get erosion, hills and rivers. It’s just that they’d be of different sizes and occur in different proportions.