Hydrogen bonding is a strong dipole-dipole interaction that occurs between a hydrogen atom covalently bonded to an electronegative atom (such as N, O, or F) and another electronegative atom. These interactions create an electrostatic attraction between molecules, causing them to stick together and form a more viscous liquid.

The stronger the hydrogen bonds, the more viscous the liquid will be. For example, water is a relatively viscous liquid because of the strong hydrogen bonds between water molecules. In contrast, ethanol is a less viscous liquid because the hydrogen bonds between ethanol molecules are weaker.

The viscosity of a liquid also depends on its temperature. As the temperature of a liquid increases, the kinetic energy of the molecules increases, causing them to move more quickly and break apart the hydrogen bonds. This results in a decrease in viscosity.

For example, water is more viscous at room temperature than it is at higher temperatures. This is because the hydrogen bonds between water molecules are stronger at room temperature, causing the liquid to flow more slowly.