Ever wondered why water droplets form on leaves or how plants move water from roots to leaves? It’s all about cohesion and adhesion. These forces, powered by intermolecular forces like hydrogen bonding and van der Waals forces, are key to how liquids, especially water, behave.
Cohesion and adhesion differ in the molecules they affect. Cohesion is about the forces between molecules of the same substance. For example, it’s what keeps water molecules together. Adhesion, on the other hand, is about forces between different substances, like how water sticks to a glass container.
Cohesive forces come from hydrogen bonding and Van der Waals forces. Adhesive forces can come from electrostatic or mechanical interactions.
The strength of cohesive and adhesive forces changes how liquids act and stick to surfaces. If adhesive forces are stronger, liquids spread out and stick to surfaces, creating a thin film. This is called wetting. But if cohesive forces are stronger, liquids form droplets or beads on surfaces.
Here are some everyday examples:
- Surface tension: Cohesive forces make liquids’ surfaces contract, creating a shape that minimizes surface area. This lets water droplets form on leaves and allows insects to walk on water.
- Capillary action: Adhesive forces and cohesive forces let water rise in thin tubes, like in plant stems, against gravity.
- Meniscus formation: The balance between cohesive and adhesive forces shapes the liquid surface in containers, making it concave or convex.
Effects of Cohesion and Adhesion in Nature
In nature, cohesion and adhesion work together to create amazing phenomena. These forces, based on polarity and dipole-dipole interactions, show up in many ways. They affect liquids and how they interact with solids, leading to surface tension, capillary action, and water’s special properties in plants.
Surface Tension
Surface tension comes from cohesion, where molecules stick together strongly. This is very clear in water, where hydrogen bonds make molecules cluster together. This makes water droplets form spheres and lets insects like water striders walk on water without sinking.
Capillary Action
Capillary action shows how cohesion and adhesion work together in nature. When a liquid touches a narrow space, like a thin tube, its molecules stick to the solid surface. This balance lets the liquid move up against gravity. It’s key for plants to move water and nutrients, and for things like paper towels to soak up liquids.
Water Properties in Plants
Plants need the cohesive and adhesive properties of water to live. In plants, water molecules stick together strongly, forming columns from roots to leaves. At the same time, they stick to the plant’s walls, helping water move up against gravity. This balance lets plants send water and nutrients from the soil to their leaves, supporting life and growth.
| Property | Cohesion | Adhesion |
|---|---|---|
| Surface Tension | Strong cohesive forces between water molecules create an elastic surface film | Not applicable |
| Capillary Action | Cohesive forces within the liquid column help maintain its integrity | Adhesive forces between the liquid and the solid surface drive the upward movement |
| Water Transport in Plants | Cohesion allows water to form continuous columns in the xylem vessels | Adhesion between water and xylem walls facilitates upward movement against gravity |
