A more fluid bond (Image: Bally Scanlon/Getty)
Read more: “Rewriting the textbooks: When science gets it wrong“
There is a reason why ice floats on water, and it is called the hydrogen bond. Whatever that is.
Nobel laureate thought he knew. In fact, the , which concerns itself with such things, still bases its official definition on the one that appears in Pauling’s classic 1939 book The Nature of the Chemical Bond.
A hydrogen bond, in this picture, is what forms when a hydrogen atom that is already stably bound into one molecule finds itself attracted to a highly electronegative atom – one like oxygen, nitrogen or fluorine that likes to suck in electrons and turn into a negatively charged ion – elsewhere in the same molecule or in a nearby molecule.
Take good old H2O. The two hydrogen atoms of a water molecule are bound covalently, through shared electrons, to its central oxygen atom. But should a second water molecule come near, the electron orbiting one of the hydrogen atoms can be drawn towards the second molecule’s electron-hungry oxygen.
Ice is less dense than liquid water because, when water molecules are cold and still, weak hydrogen bonds between them keep them consistently at arm’s length. In free-flowing water, however, the bonds are continually breaking and reforming, allowing the molecules to jostle closer together.
That is all fine and dandy. But this traditional picture also implies a strict range of admissible hydrogen-bond strengths. Over the past 40 years, though, reams of evidence about much weaker bonds, including ones between…
