Van der Waals force
In chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer only to London forces: those forces which arise from induced rather than permanent dipoles. The forces are named after Johannes Diderik van der Waals.
Van der Waals interactions are observed in noble gasses, which are very stable and tend not to interact, that is why it is difficult to condense them into liquids. However, the larger the molecule of the noble gas (the more electrons it has), the easier it is to condense the gas into a liquid. This happens because when the electron cloud surounding the gas gets large, it does not form a perfect sphere around the nucleus. Rather, it forms an oval, which has a slight negative charge on one side and a slight positive charge on the other. The atom becomes a temporary dipole. This induces the same shift in neighboring atoms and spreads from one atom to the next. Unlike charges attract and the induced dipoles are held together by dispersion force (or van der Waals force).
The van der Waals force is the force to which the gecko's unique ability to cling to smooth surfaces is attributed. A gecko can hang on a glass surface using only one toe. In 2003 a kind of synthetic was created using this principle.
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