How do hydrogen bonds differ in strength from van der Waals forces?

Hydrogen bonds are significantly stronger than van der Waals forces.

Hydrogen bonds and van der Waals forces are both types of intermolecular forces, which are forces that occur between molecules. However, they differ greatly in terms of strength. Hydrogen bonds are considered to be the strongest type of intermolecular force, while van der Waals forces are the weakest.

Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine) and is attracted to another electronegative atom in a different molecule. This results in a strong dipole-dipole interaction, which is much stronger than the temporary dipoles that cause van der Waals forces. The strength of a hydrogen bond can be up to 30 times greater than a van der Waals force.

Van der Waals forces, on the other hand, are weak forces that occur between all atoms and molecules. They are caused by temporary fluctuations in the electron distribution around an atom or molecule, which create a temporary dipole that induces a dipole in a neighbouring atom or molecule. This induced dipole then attracts the original atom or molecule, creating a weak force of attraction known as a van der Waals force. These forces are much weaker than hydrogen bonds because they are only temporary and depend on the distance between the atoms or molecules.

In terms of their effects on the properties of substances, the strength of hydrogen bonds means that substances that can form hydrogen bonds often have higher boiling points, melting points, and viscosities than similar substances that can only form van der Waals forces. This is because more energy is required to break the stronger hydrogen bonds and change the state of the substance.

In summary, while both hydrogen bonds and van der Waals forces are important intermolecular forces, hydrogen bonds are significantly stronger due to their dipole-dipole nature and the high electronegativity of the atoms involved. This results in substances with hydrogen bonding often having different physical properties compared to those that only exhibit van der Waals forces.