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Hydrogen Bonding Some atoms, like oxygen and nitrogen, have a high affinity for electrons, while other atoms, like hydrogen, have a low affinity for electrons. When atoms with differing affinities for electrons are bonded to one another, the high electron affinity atom (i.e., nitrogen or oxygen) pulls on the shared electrons more than the low electron affinity atom. Since electrons are negatively charged, the oxygen or nitrogen atoms become slightly negative, indicated by a partial charge (δ−). At the same time, the hydrogen atom that has “lost” some of the shared electrons has a very weak positive charge (δ+). The resulting partial positive and negative portions of the atoms can become attracted to and attract partially positive and negative atoms from nearby molecules or even within the same molecule.

 

The resulting interaction between a partial positive component of one molecule and a partial negative component of another molecule is called a hydrogen bond . It is called a hydrogen bond because of the involvement of hydrogen as the low electron affinity atom; the high electron affinity atom is typically nitrogen or oxygen in foods and cooking. Given the hydrogen bonding potential for water, as H2 O, and the presence of water in many foods and cooking processes, hydrogen bonding is a very important inter- molecular interaction.

 

Let’s look at the example of starch. Anyone who has made gravy with cornstarch has experienced the frustration of adding hot water to dried starch and the resulting blob at the bottom of the dish. As we will learn later, starch is a long polymer of glucose molecules (from hundreds to thousands of glucose molecules) resulting in tens of thousands of ─OH groups.