A new study has found a strange variety of bond that acts as a hybrid of covalent bonds and hydrogen bonds. This has raised questions about how chemical bonds are defined.
Hydrogen bonds are typically thought of as weak electrical attractions, while covalent bonds, on the other hand, are strong chemical bonds that hold together atoms within a molecule and result from electrons being shared among atoms.
Now, researchers report that an unusually strong variety of hydrogen bond is in fact a hybrid, as it involves shared electrons, blurring the distinction between hydrogen and covalent bonds.
Experiments carried out by scientists show that chemical bonding is a “continuum”
“Our understanding of chemical bonding, the way we teach it, is very much black and white,” says chemist Andrei Tokmakoff of the University of Chicago. “The new study shows that there’s actually a continuum.”
Tokmakoff and colleagues characterized the hybrid bond by observing groups of atoms called bifluoride ions, which are made up of a single hydrogen atom placed between a pair of fluorine atoms in water.
According to conventional knowledge, the hydrogen atom is bound to one fluorine by a covalent bond, and to the other fluorine by a hydrogen bond.
Results of the experiment give scientists new knowledge about the nature of chemical bonds
The researchers used infrared light to set bifluoride ions vibrating and measured the hydrogen atoms’ response. The measurements revealed a series of energy levels at which the hydrogen atoms vibrated
In a typical hydrogen bond, the spacing between those energy levels would decrease as the atom climbed further up the energy ladder. But instead, the researchers found that the spacing increased.
In that arrangement, “the difference between the covalent and [hydrogen] bond is erased and is no longer meaningful,” says study coauthor Bogdan Dereka, a chemist also at the University of Chicago.