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Henryk Sadura / Alamy Stock Photo

By David Robson and Michael Marshall

No liquid behaves quite as oddly as water. It exhibits a raft of unusual behaviours, many of which are essential for life as we know it. In our cover feature, we look at how a controversial new theory could finally explain water’s weird behaviour. Here we explain how the theory could explain 10 of water’s behaviours – and then take a quick look at its many other peculiarities.

Water’s mysteries

Picturing water as a liquid that can form two types of structure, one tetrahedral and the other disordered, could explain many of its unusual properties. Here are 10 of them.

1. Water is most dense at 4 °C

EXPLANATION: Heating reduces the number of ordered, tetrahedral structures in favour of a more disordered arrangement in which molecules are more densely packed. However, the heat also agitates the molecules in the disordered regions, causing them to move further apart. Above 4 °C, this effect takes precedence, making the water less dense

2. Water has an exceptionally high specific heat capacity: it takes a lot of heat energy to raise water’s temperature by a given amount

EXPLANATION: Much of the extra heat energy is used to convert more molecules from the tetrahedral structures to the disordered structures, rather than into increasing the kinetic energy of the molecules, and hence the temperature.

3. Specific heat capacity is at …

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