Hydrogen Bonds
- Electronegative atoms such as N, O, F, and Cl (Fig. A.) pull the distribution of electrons away from other less electronegative atoms bound to them through covalent bonds (Fig. B.).
- This creates slightly positive polar atoms which are attracted to the slightly negative unshared pairs of electrons found in N and O. This +-attraction forms the basis of hydrogen bonding (Fig.C.).
- Hydrogen bonds are weak bonds, ~1/20 of covalent bonds, that are sensitive to increases in temperature. Hydrogen bonds have a strength of 4 kcal/mole in a vacuum and 1 kcal/mole in water.
- The bond length between the hydrogen and the electronegative O or N to which it is covalently bound is about 0.1 nm (Fig. D.). The bond between the H and the O or N contributing the unshared pair of electrons is about 0.2 nm.