# Is a hydrogen bond considered to be a van der Waals force?

Is a hydrogen bond considered to be a Van der Waals force?

According to the IUPAC gold book a van der Waals force is:

The attractive or repulsive forces between molecular entities (or between groups within the same molecular entity) other than those due to bond formation or to the electrostatic interaction of ions or of ionic groups with one another or with neutral molecules. The term includes: dipole–dipole, dipole-induced dipole and London (instantaneous induced dipole-induced dipole) forces.

Hydrogen bonding is a type of dipole-dipole interaction, so it would fit the definition of a van der Waals force.

The way I think of it is: van der Waals forces are anything that make a gas non-ideal, since that's how they were originally discovered and defined.

• But doesn't hydrogen bonding contain a rather sizable covalent component which would mean it doesn't fall under the IUPAC definition? – Philipp Jan 25 '15 at 14:08
• @Phillip - Sure, you could argue that. I guess it would depend on if you consider the covalent nature or the ionic nature more significant. Traditionally, it is classified as a particularly strong dipole-dipole interaction, which makes sense because we normally talk about van der Waals forces in the context of gases. – thomij Jan 25 '15 at 15:23
• The provisional IUPAC recommendation for the definition of hydrogen bond requires "evidence of bond formation" and refers to "partial covalent bond formation". This would seem to exclude the "other than those due to bond formation" requirement of the van der Waals definition. media.iupac.org/reports/provisional/abstract11/arunan_prs.pdf – DavePhD Jan 25 '15 at 23:19
• I agree with @DavePhD and the source he cited (maybe make it an answer for a more permanent record?). The goldbook however recommends, to regard an Hydrogen bond as an "electrostatic interaction", which would make it fall under the mentioned vdW description. This is one of those topics, where a pure classification is not possible - in some cases the covalent character would outweigh the ionic and in some cases it would be the other way around. – Martin - マーチン Jan 29 '15 at 2:37
• @Martin, that's why I look at it in the context of gases, which is really the only context in which it makes sense to talk about van der Waals forces as a group. In any other context, the different interactions are treated separately. – thomij Jan 29 '15 at 5:51

I'm a physics grad student. From my understanding, H-bond is not what people typically mean by van der waals force. H-bond is just basic dipole-dipole interaction with essentially fixed dipole moments (the dipoles are simple result of difference of electronegativity within each molecule). Van der waals force (like interactions between H2 molecules) typically mean induced-dipole - induced-dipole interaction. (The dipole of an isolated molecule is zero)

One major consequence of the difference is that dipole-dipole force scale with $$r^{-4}$$.

I'm not totally sure of the above...my understanding is Efield_dipole scale as $$r^{-3}$$. F=-d/dr U = d/dr ( DipoleMoment $$\cdot$$ Efield_dipole ) = $$r^{-4}$$

Whereas van der waals have higher order distance dependency because each dipole moment themselves are induced by electric field which depends on distance. So, van der waals force scale with $$r^{-6}$$