Glossary
hydrogen bond
A hydrogen bond is a weak attraction between a hydrogen already bonded to oxygen, nitrogen or fluorine and a nearby lone pair on another molecule, or on another part of the same molecule.
A hydrogen bond is a weak attraction, not a bond in the covalent sense: a hydrogen atom that is already attached to oxygen, nitrogen or fluorine is pulled by those atoms so that it carries a slight positive charge, and it is then attracted to a lone pair on a neighboring molecule or on another part of the same molecule, which is how a protein chain folds back on itself. Each one is roughly a twentieth as strong as a covalent bond, and that weakness is the point — hydrogen bonds form and break constantly at body temperature, which is what lets water flow, proteins fold and DNA unzip. The consequences are large. Water boils far above the temperature its size would predict because each molecule is tied to several others; ice floats because its hydrogen bonds lock into an open lattice; and the two strands of DNA hold together by hydrogen bonds between paired bases, which the cell can separate without breaking the strand itself.
Taught in
Related terms
- covalent bond — A covalent bond is a shared pair of electrons between two atoms, the usual bond between nonmetals and the bond that holds molecules together.
- matter — Matter is anything with mass that takes up space, and it exists as a solid, a liquid, a gas or a plasma.
Source: NIST periodic table and reference data for the atomic masses and half-life figures, NIH PubChem for the substance data, and NIST Special Publication 811 for the unit conventions — the same sources the chemistry guide cites. All three are US federal government material, not subject to copyright in the United States. Every definition, example and calculation above was written for this course; no dictionary or textbook text is reproduced. (NIST and PubChem accessed 2026-10-26; definitions written 2026-10-27)