Hydrogen bond

Figure 1. A depiction of hydrogen bonding between water molecules.

A hydrogen bond is an attraction between molecules (an intermolecular attraction). Hydrogen bonds can form between molecules that have N-H, O-H, F-H, and Cl-H bonds.

A hydrogen bond is not a "bond" in the same sense as the chemical bonds that hold the atoms in a molecule together. They are about 10-100 times weaker than a covalent bond (an intramolecular bond), but they are stronger than other intermolecular attractions. A hydrogen bond can occur between molecules when the molecules are polar (they have an electric dipole) and the dipole involves a hydrogen atom covalently bonding with a very electronegative atom such as Nitrogen, Oxygen, or Fluorine. The slight positive and slight negative dipole moments in two different molecules attract the molecules to each other, as seen in Figure 1.

Compared to compounds that cannot hydrogen bond, compounds that do participate in hydrogen bonding with each other will have higher boiling points and melting points. These higher boiling and melting points are due to the strong intermolecular forces, which translate to a higher specific heat capacity because those stronger forces between the molecules require more energy to overcome.

The presence of strong hydrogen bonds in water explains many of its unique properties. Water is a liquid at room temperature, when most other molecules of a similar size are gases. It also exhibits a high specific heat capacity, which explains its ability to regulate temperature.

To learn more about hydrogen bonds, see the Chemistry LibreText page about hydrogen-bonding and water.

For Further Reading

• Molecule
• Electric dipole
• Specific heat capacity
• Water
• Chemical bond
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