By Harold McGee
A fourth kind of chemical bond is very weak indeed, between a hundredth and a ten-thousandth as strong as a molecule-making covalent bond. These van der Waals bonds, named after the Dutch chemist who first described them, are the kind of flickering electrical attraction that even nonpolar molecules can feel for each other, thanks to brief fluctuations in their structures. Where electrically polar water is held together as a liquid by hydrogen bonds, nonpolar fat molecules are held together as a liquid and given their appealingly thick consistency by van der Waals bonds. Though these bonds are indeed weak, their effect can add up to a significant force: fat molecules are long chains and include dozens of carbon atoms, so each fat molecule can interact with many more other molecules than a small water molecule can.