MODULE 6: Water
Learning Objective 16: Define hydrogen bonds and describe how they form. Listen to Learning Objective 16
Atoms in the water molecule are held together by polar covalent bonds, as we saw in the previous learning objective. The unequal share of electrons in the OH polar covalent bonds results in the oxygen atom having a slightly negative
charge density (δ-) and hydrogen atom having a slightly positive charge (δ+). The slightly negative Oδ- in one water molecule is attracted to the slightly positive Hδ+ of a neighboring water molecule as shown in figure 2.11 below.
Figure 2.11 Hydrogen bonds are relatively weak. They occur between atoms of different molecules and are shown as a dotted line rather than a solid line. Covalent bonds are stronger, occur between atoms of the same molecule and are shown as solid lines. Art by OpenStax College – CC-BY
The electrical attraction between Hδ+ in one molecule and Oδ- in another molecule is called a hydrogen bond. (Hydrogen bond can also be formed between Hδ+ in one molecule and Nδ- in
another molecule). A hydrogen bond is a weaker type of attraction, but many hydrogen bonds add up. Hydrogen bonds explain many of the properties of water. Activity 2.7 below shows how hydrogen bonds form.
Activity 2.7 Adjust the lever (top right) in the interactive simulation here to speed up the motion of water molecules. Note that hydrogen atoms of a molecule and oxygen atoms of another molecule are always positioned in front of each other. Simulation by Chris Bruce/PBS LearningMedia
Watch the simulation here: https://ny.pbslearningmedia.org/resource/arct15sci-water/water-simulation/
Anatomy and Physiology Preparatory Course Textbook 2nd Ed. | Carlos Liachovitzky | CC BY-NC-SA 4.0
45
