06/11/2025
Van der Waals forces are weak intermolecular forces that arise from attractive or repulsive interactions between molecules or atoms. They are not true chemical bonds (like covalent or ionic bonds) but rather physical interactions that play a big role in many natural and biological processes—such as why geckos stick to walls or how gases condense into liquids.
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🧲 Types of Van der Waals Forces
1. London Dispersion Forces (Instantaneous Dipole–Induced Dipole)
Occurs in: All molecules (even nonpolar ones like helium or oxygen gas).
How it happens:
At any instant, electrons in an atom or molecule may be unevenly distributed.
This creates a temporary dipole.
That dipole can induce a dipole in a neighboring atom or molecule.
The two temporary dipoles attract each other weakly.
Strength: Weakest type, but increases with:
The size (number of electrons) of the molecule
The surface area (more contact = stronger attraction)
💡 Example: Noble gases like argon can liquefy at low temperatures due to these forces.
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2. Dipole–Dipole Forces
Occurs in: Polar molecules (those with permanent dipoles).
How it happens:
One molecule’s positive end attracts another molecule’s negative end.
Strength: Stronger than London dispersion, but weaker than hydrogen bonds.
💡 Example: Between molecules of HCl — the positive hydrogen end of one HCl attracts the negative chlorine end of another.
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3. Dipole–Induced Dipole Forces
Occurs in: Between a polar and a nonpolar molecule.
How it happens:
The electric field of a polar molecule distorts the electron cloud of a nearby nonpolar molecule.
This creates an induced dipole in the nonpolar molecule → attraction forms.
💡 Example: Between water (polar) and oxygen gas (nonpolar).
Mazi Uchechukwu
