Properties of Water- Cohesion and Adhesion: Videos & Practice Problems

Water exhibits unique properties due to its molecular structure, particularly through the concepts of cohesion and adhesion. Cohesion refers to the tendency of water molecules to stick together, a phenomenon primarily caused by hydrogen bonding. The prefix "co-" in cohesion signifies "together," highlighting how water molecules bond with one another, forming a cohesive network. This is visually represented by the green lines in diagrams, which illustrate the hydrogen bonds connecting water molecules.

In contrast, adhesion describes the ability of water molecules to adhere to other substances, such as glass. This interaction occurs when water molecules form bonds with polar or charged surfaces, exemplified by the purple lines in diagrams that connect water molecules to glass. Notably, water does not adhere to all materials; it specifically interacts with polar substances, which allows for these adhesive properties.

The interplay of cohesion and adhesion contributes to the phenomenon known as surface tension, defined as the resistance of a liquid's surface to external force. Surface tension arises from the cohesive forces among water molecules, creating a "skin" on the water's surface. This property enables certain organisms to exploit surface tension, allowing them to walk on water or remain suspended at the surface. For instance, a paper clip, which is denser than water, can float on the surface if placed carefully, demonstrating the effects of surface tension. However, if sufficient force is applied, the surface tension can be broken, causing the paper clip to sink.

Ultimately, the cohesive and adhesive properties of water, driven by its polarity and hydrogen bonding capabilities, are fundamental to many biological processes and are essential for life. As we explore further, we will delve into additional properties of water that play critical roles in various ecological and physiological contexts.

Cohesion, surface tension, and adhesion are essential properties of water molecules that arise from hydrogen bonding. These properties are crucial for various biological and physical processes. Cohesion refers to the attraction between water molecules, which allows them to stick together, contributing to phenomena such as water droplets forming on surfaces. Surface tension is the result of cohesive forces at the surface of water, creating a "skin" that can support small objects. Adhesion, on the other hand, describes the attraction between water molecules and different substances, enabling water to climb up plant roots and stems through capillary action.

Understanding these properties is vital, as they play significant roles in the environment and living organisms. For instance, the high surface tension of water allows insects to walk on its surface, while cohesion and adhesion are essential for the movement of water in plants. The underlying mechanism for these properties is the polar covalent bonds within water molecules, which lead to the formation of hydrogen bonds between them. This unique bonding capability is what makes water a remarkable substance, influencing its behavior in various contexts.