Structural Biochemistry/Unique Properties/Cohesive Behavior
Cohesive and Adhesive Behavior of Water[edit | edit source]
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Cohesion and adhesion in water are caused by the intermolecular attraction between the partial negative oxygen of one water molecule, and the partial positive hydrogen of another molecule. This non-covalent bond is known as a hydrogen bond. Water is strongly cohesive because each molecule may make four hydrogen bonds with other water molecules in a tetrahedral configuration. Surface tension is a result of the cohesion of water molecules at the surface of a body of water. The ability of some insects to float on water is accounted for because of this property. Conversely, the adhesive property of water (water bonding to a molecule other than water) allows for capillary action to occur such as trees transporting water from the ground to the topmost branches.
Adhesive: water molecules are attracted to other materials. For example, if you place a capillary glass tube open ended into a container with water, you will observe a concave up curve as a result of water molecules attracted to the polar glass capillary tube.
Cohesive: water molecules are attracted to other water molecules. For example, if you place a capillary glass tube open ended into a container with mercury, you will observe a concave down curve because the glass is polar which doesn’t attract with mercury. As shown in the figured.