The question of whether water is scientifically “wet” highlights the difference between everyday language and precise scientific definitions. While intuitively, water feels wet, a deeper look into its molecular interactions reveals a more nuanced understanding. This scientific perspective helps clarify why the term “wet” is applied to objects that come into contact with water, rather than to water itself.
What Does “Wet” Really Mean?
From a scientific standpoint, “wetness” describes the state of a solid surface when a liquid adheres to and spreads across it. It is not an inherent property of the liquid itself but rather a description of the interaction between a liquid and a solid. This interaction depends on a balance of intermolecular forces: cohesion and adhesion.
Cohesive forces are the attractive forces between molecules of the same substance, causing them to stick together, like water molecules bonding with other water molecules. Adhesive forces, conversely, are the attractive forces between molecules of different substances, such as water molecules and the surface of an object. When the adhesive forces between a liquid and a solid surface are stronger than the cohesive forces within the liquid, the liquid spreads out, and the surface is considered “wet.” If cohesive forces are stronger, the liquid tends to bead up, minimizing contact with the surface, as seen with water on a waxy surface.
The Unique Properties of Water
Water (H₂O) possesses unique molecular properties that allow it to make other substances wet. Each water molecule is polar, meaning it has a slight positive charge on the hydrogen atoms and a slight negative charge on the oxygen atom due to the uneven distribution of electrons. This polarity results from its bent molecular geometry, where the oxygen atom pulls electrons more strongly than the hydrogen atoms.
This polarity enables water molecules to form hydrogen bonds with each other, where the positive end of one water molecule is attracted to the negative end of another. These strong intermolecular attractions contribute to water’s high cohesive forces, making water molecules cling together. Simultaneously, water’s polarity also allows it to form strong adhesive bonds with other polar surfaces, such as glass or cotton.
The cohesive forces among water molecules are also responsible for surface tension, which is the tendency of liquid surfaces to shrink into the minimum surface area possible. While water has relatively high cohesive forces due to hydrogen bonding, its strong adhesive properties with many materials mean it readily spreads across and clings to those surfaces, thereby making them wet.
So, Is Water Wet?
Based on the scientific understanding of “wetness,” water itself is not inherently wet. Instead, water is the agent that causes other objects or surfaces to become wet. The term “wet” describes the outcome of an interaction where a liquid, like water, adheres to a solid surface.
For something to be wet, there must be a liquid present that is sticking to a separate material. Since water does not have a solid surface for its own molecules to adhere to in the way it adheres to other materials, it cannot be “wet” in the scientific sense. When you feel water, the sensation of “wetness” arises because the water molecules are adhering to your skin. Water makes things wet due to its adhesive properties, but it is the object that is wet, not the water itself.