Asked by: Matt Barker, St Albans
Water has many strange properties, including a high surface tension, an ability to dissolve more things than any other common liquid, and a solid state (ice) that floats. These strange properties come from water’s simple structure. Its atoms form a chevron shape with a slightly negatively charged oxygen and positive hydrogens. This allows water to bind to and dissolve both negatively and positively charged molecules.
Meanwhile, the hydrogen of one water molecule is attracted to the oxygen of another. Within a liquid these attractions briefly hold the molecules together, generating the high surface tension. This network is frozen in place when the water is cooled, leaving large gaps. As a result, the sponge-like ice floats on the liquid. In contrast, other chemicals form tightly packed solid crystals that are more dense than the liquid and so sink.