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Van der Waals Forces

Simple Explanation

Van der Waals forces are weak attractions between molecules, caused by temporary, shifting imbalances in electron distribution that create brief, tiny dipoles — even in molecules with no permanent polarity at all.

Why Do We Need It?

These are the only forces holding nonpolar substances like oxygen, nitrogen, and the noble gases together as liquids or solids at all — without them, nothing would ever condense into a liquid or freeze into a solid unless it also had stronger polar or ionic interactions.

Why Does This Work?

Electrons are constantly moving, so at any given instant they might happen to be unevenly distributed across a molecule, creating a fleeting, temporary dipole. That temporary dipole induces a matching temporary dipole in a neighbouring molecule, and the two weakly attract each other — an instant later the electrons shift again, but on average this creates a constant weak attractive pull between molecules.

Real-Life Example

Why gecko feet stick to walls

Geckos can climb smooth vertical glass using only their feet, with no glue or suction.

A gecko's feet are covered in millions of microscopic hair-like structures that get so close to a surface that van der Waals forces between the hairs and the surface molecules add up to a strong enough net force to support the gecko's weight.

Practice

Why can nonpolar substances like oxygen gas still be cooled into a liquid?

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Common mistake

Assuming van der Waals forces are negligible or unimportant because they are weak compared to covalent or ionic bonds — for large molecules with many atoms, van der Waals forces add up across the whole molecule and can become quite significant, which is why larger nonpolar molecules generally have higher boiling points than smaller ones.

Quick Review

Van der Waals forces come from temporary, fluctuating electron distributions.
They are the weakest type of intermolecular force, but exist between all molecules.
They are the only attraction holding purely nonpolar substances together as liquids/solids.