Summary
Highlights
Van der Waals forces are attractive forces between molecules that are very close together. These intermolecular forces are significantly weaker than the chemical bonds holding atoms within a molecule.
Molecules are electrically neutral but can be polar if electrons are unevenly distributed, creating permanent poles of electrical charge, similar to a magnet. Water (H2O) is an example: oxygen attracts electrons more strongly than hydrogen, leading to a partial negative charge around oxygen and partial positive charges around hydrogen atoms. This unequal sharing forms polar covalent bonds and makes the entire water molecule polar due to its bent shape.
When polar molecules are near each other, their oppositely charged poles attract, leading to Van der Waals forces. A particularly strong type, hydrogen bonding, occurs between hydrogen in one polar molecule and oxygen, nitrogen, or fluorine in another.
Nonpolar molecules lack permanent poles but can briefly become polar due to the constant movement of electrons. This temporary uneven distribution creates momentary positive and negative poles, which can induce temporary polarity in neighboring molecules, resulting in weak Van der Waals attractions.
Van der Waals forces explain two key properties: cohesion (attraction between like molecules, seen in water beading up) and adhesion (attraction between unlike molecules, like how geckos climb surfaces by forming millions of weak molecular connections).
In summary, Van der Waals forces are intermolecular attractive forces, distinct from chemical bonds. They occur in permanently polar molecules (like water) and transiently in nonpolar molecules. Hydrogen bonds are a strong type of Van der Waals force. These forces are responsible for cohesion and adhesion.