Structural Biochemistry/Unique Properties/Cohesive Behavior

Cohesive and Adhesive Behavior of Water
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.