A hydrogen bond links a hydrogen to an O or N
- The idea
- Predict
- See it
- Why
- Check
The idea
“A hydrogen bond is a hydrogen on one molecule bonding to a hydrogen on another.”
The name sounds like two hydrogens linking up, so that's what many people draw. It's really named for the one hydrogen that bridges two molecules.
The short version
The mistake: A hydrogen bond is a hydrogen on one molecule bonding to a hydrogen on another.
What's actually true: In water, a hydrogen bond is the attraction between a slightly positive hydrogen and the slightly negative oxygen of a neighbor.
- Oxygen is electronegative, meaning it pulls shared electrons toward itself. That leaves water's oxygen slightly negative and each hydrogen slightly positive.
- Opposite partial charges attract. A hydrogen bond is the pull between a hydrogen bonded to O or N and a slightly negative O or N nearby, often on another molecule.
- Two hydrogens can't form one, because both are slightly positive and repel. The name comes from the single hydrogen that bridges the gap.
On the exam: A hydrogen bond pairs a slightly positive H with a slightly negative O or N. Two hydrogens repel.