Read more: 鈥�Rewriting the textbooks: When science gets it wrong鈥�
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鈥檚 classic 1939 book The Nature of the Chemical Bond.
Advertisement
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 鈥� one like oxygen, nitrogen or fluorine that likes to suck in electrons and turn into a negatively charged ion 鈥� 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鈥檚 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鈥檚 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 hydrogen and elements like carbon, which are not very electronegative, have come to light.
Six years ago, IUPAC set up a committee to clear up the confusion. Its conclusion, set out in a published last year, is that the hydrogen bond is a far fuzzier entity than we thought. 鈥淚t is not an interaction with sharp boundaries,鈥� says from the Indian Institute of Science in Bangalore, a member of the IUPAC committee.
This is about more than just semantics, Desiraju says. A new definition will counter a widespread misconception among chemists about when and where hydrogen bonds can occur, and encourage them to consider the bond鈥檚 influence in new situations 鈥� for example, in allowing organic molecules to form and react in ways never thought possible. Exploring such avenues could help steer us away from our current dependence on toxic and expensive catalysts containing precious metals towards cheaper, greener organic-based alternatives.
Read previous article: 鈥�Rewriting the textbooks: Confusion over nuclear fission鈥�
Read next article: 鈥�Rewriting the textbooks: When a gene isn鈥檛 a gene鈥�
