Bonds in limbo

This exercise is a part of Educator Guide: Chemical Bond Acts Like a Mash-Up / View Guide

Directions for teachers: Ask your students to read the online Science News article This weird chemical bond acts like a mash-up of hydrogen and covalent bonds,” which explores a new type of chemical bond, and answer the following questions. A version of the story, “Chemical bond acts like a mash-up,” can be found in the January 30, 2021 issue of Science News.

1. Define hydrogen bonds and covalent bonds based on the information provided in the Science News article. Of the two types of bonds, which is not considered a “true chemical bond?”  

Hydrogen bonds result from weak attractions between atoms in one molecule to oppositely charged atoms in a neighboring molecule. Covalent bonds result from electrons being shared among atoms, typically within a molecule. Unlike the covalent bond, the hydrogen bond is not considered a true chemical bond.

2. What is the new type of bond that scientists discovered? What makes it special?

Researchers discovered what’s called a hydrogen-mediated chemical bond. At first it was thought to be an unusually strong variety of hydrogen bond. But experiments revealed that the bond is a hybrid of a hydrogen bond and a covalent bond, as it involves shared electrons—a characteristic of covalent bonds.

3. Where was the new bond found? Name and describe the molecule that contains the new bond.

The new bond was found in bifluoride ions in water. A bifluoride ion consists of a hydrogen atom sandwiched between two fluorine atoms.

4. According to the rules of chemistry, how should the molecule have been bound together? How was the molecule actually bound together?

According to the rules of chemistry, the hydrogen atom in one bifluoride molecule should be loosely bound to one fluorine atom via hydrogen bonding and closely bound to the other fluorine atom via covalent bonding. Instead, the hydrogen atom was shared equally between the fluorine atoms.

5. What did computer simulations reveal about the new bond’s behavior?

As the fluorine atoms moved closer together and squeezed the hydrogen atom, the normal hydrogen bond became stronger until all three atoms began sharing electrons as in a covalent bond.

6. What does chemist Bogdan Dereka say about the discovery?

The hydrogen-mediated bond erases the difference between covalent and hydrogen bonds so that the distinction is no longer meaningful.

7. Why is understanding strong hydrogen bonds important?

Strong hydrogen bonds are thought to play a role in transporting hydrogen ions,

a process crucial for powering living cells and for technologies such as fuel cells. Better understanding these bonds could shed light on a variety of effects.

8. What are the big-picture implications of the discovery?

The discovery has implications for scientists’ fundamental understanding of what a chemical bond is, as well as what qualifies as a molecule.