No, water is not adhesive to itself; rather, it is cohesive to water. The terms cohesion and adhesion describe two distinct types of molecular attraction, both crucial to understanding water's unique properties.
Understanding Cohesion vs. Adhesion
According to scientific definitions, which align with the provided reference from June 5, 2018:
- Cohesion: This property is defined as "Water is attracted to water." It refers to the attractive forces between like molecules. For water, these strong cohesive forces are primarily due to hydrogen bonds that form between individual water molecules.
- Adhesion: This property is defined as "Water is attracted to other substances." It describes the attractive forces between water molecules and molecules of a different type.
Therefore, when water molecules are attracted to other water molecules, this phenomenon is precisely defined as cohesion, not adhesion. Adhesion would describe water's attraction to a different surface, such as glass, fabric, or soil particles.
Key Differences Summarized
To further clarify, consider the fundamental distinction between these two intermolecular forces:
| Property | Definition | Interaction Between | Example |
|---|---|---|---|
| Cohesion | Water attracted to water | Like molecules (e.g., water-water) | Water droplets forming, surface tension, water flowing in a stream |
| Adhesion | Water attracted to other substances | Unlike molecules (e.g., water-glass, water-fabric) | Water sticking to glass, a wet sponge absorbing water, water clinging to plant roots |
Practical Insights and Examples
The interplay between cohesion and adhesion is fundamental to many natural processes and everyday observations, showcasing water's remarkable versatility.
Examples of Cohesion in Action:
- Surface Tension: Water's high surface tension, which allows insects like water striders to walk on water or causes water to form beads on a waxy surface, is a direct result of strong cohesive forces pulling the surface molecules inward.
- Droplet Formation: Raindrops and dew drops assume a spherical shape because the cohesive forces pull the water molecules together, minimizing their surface area.
- Water Transport in Plants: Along with adhesion, cohesion plays a vital role in the capillary action that draws water up from the roots to the leaves of plants. Water molecules "pull" each other up through narrow tubes (xylem) within the plant against gravity.
Examples of Adhesion in Action:
- Meniscus Formation: When water is in a narrow glass cylinder or beaker, the water level often curves upwards at the edges. This concave shape (meniscus) is due to the adhesive forces between water and glass being stronger than the cohesive forces within the water.
- Wetting Surfaces: Water "wets" a clean glass surface or fabric because the adhesive forces between water and the material's molecules are significant, allowing the water to spread out.
- Absorbing Materials: Materials like paper towels or sponges absorb water effectively because of the strong adhesive forces between water molecules and the fibers of the material, drawing water into their porous structures.
In conclusion, while water exhibits strong attractive forces, it is crucial to use the correct scientific terminology. Water's attraction to itself is cohesion, and its attraction to other materials is adhesion.
