A New Type Of Surprisingly Strong Chemical Bond Discovered

Scientists have found a new chemical bond, and this one seems to be significantly stronger than it has to be.

This new bond reveals the divide between powerful covalent bonds, which bind molecules together, and weak hydrogen bonds, which form between molecules and can be broken by something as simple as stirring salt into a glass of water.

We know that ionic bonds link metals and non-metals to form salts. Strong covalent bonds bind molecules like carbon dioxide and water. The weaker hydrogen bonds form because of an electrostatic type of attraction between hydrogen and a more negatively charged atom or molecule.

These three are relatively stable and they last for extended periods of time.

During a chemical reaction, bonds form and break. There are intermediate states involved.

The new study has focused on prolonging the time for these intermediate states so we can study them. The result was that they found out hydrogen bond with the strength of a covalent bond, binding atoms together into something resembling a molecule.

They dissolved a hydrogen-fluoride compound in water and watched how the hydrogen and fluorine atoms interacted. The fluorine atoms were attracted to the hydrogen atoms because of imbalances of positive and negative charges across their surfaces, the classic structure of a hydrogen bond. Two fluorine atoms were on both sides of each hydrogen atom.

The sandwiched atoms were bound with more strength than typical hydrogen bonds. The bond became as strong as covalent bonds and resembling molecules because hydrogen atoms were bouncing back and forth between the fluorine atoms.

The mechanism involved was electrostatic, which meant it involved the sort of differences in positive and negative charge that define hydrogen bonds.

Bond strength of the new bonds was around 45.8 kilocalories per mol (a unit of chemical bonding energy), greater than some covalent bonds. For instance, Nitrogen molecules have strength of about 40 kcal/mol.

Adding to it, hydrogen bond typically has an energy of about 1 to 3 kcal/mol.

Researchers at the Max Planck Institute for Polymer Research in Germany, who were not involved in the study, wrote that this unusual bond blurs the clear categories of chemistry.

They said that the existence of a hybrid covalent-hydrogen bonded state not only challenges our current understanding of what a chemical bond exactly is but also offers the opportunity to better understand chemical reactions.

Water has similar bonds, but they are not existent for such long. They haven’t been observed yet. This study could have paved way for “deeper understanding of strong bonding” and the intermediate reaction states.

Journal Reference:
Bogdan Dereka, Qi Yu, Nicholas H. C. Lewis, William B. Carpenter, Joel M. Bowman, Andrei Tokmakoff Crossover from hydrogen to chemical bonding Science  08 Jan 2021 DOI: 10.1126/science.abe1951