Because they are the result of the attraction between partial charges rather than full charges, hydrogen bonds are much weaker than ionic or covalent bonds. Ionic and covalent bonds attract the atoms of different substances together to form the molecules of compounds, while hydrogen bonds are forces that tend to attract molecules to each other. An example of hydrogen bonding is the attraction between individual water molecules while the attraction between the atoms of hydrogen and oxygen within each water molecule represents covalent bonding.
A hydrogen bond is formed when a positively polarized hydrogen atom in one molecule is attracted to a highly electronegative atom in another molecule. In the example of water molecules, the negatively charged oxygen atom in one water molecule attracts the positively charged hydrogen atom in another water molecule. Oxygen atoms tend to steal electrons away from the hydrogen atoms within molecules. When this occurs within a water molecule, the electron loss creates a hydrogen atom with a partial positive charge, which is then attracted to a negatively charged oxygen atom in another water molecule.
The hydrogen bonds that form between water molecules cause them to stick together. This gives water a high boiling point temperature because a greater degree of heat energy is required to break the intermolecular hydrogen bonds. Many organic substances that are required to sustain life, such as nucleic acids and proteins, contain hydrogen bonds. Although these bonds are weaker than the internal ionic or covalent bonds existing between the atoms within molecules, the accumulated strength of hydrogen bonds within living organisms is highly significant and plays an important role in maintaining stability.