Cohesion
Definition and meaning of Cohesion in chemistry.
Cohesion is the mutual attraction between molecules of the same substance, caused by intermolecular forces such as hydrogen bonding, dipole-dipole interactions, and van der Waals forces, which holds the molecules together.
In more detail
Cohesive forces determine many bulk liquid properties, including surface tension, viscosity, and the tendency of a liquid to resist separating into droplets. Water shows unusually strong cohesion because its molecules form extensive hydrogen bonds with one another, giving it one of the highest surface tensions of any common liquid. Cohesion is distinct from adhesion, which is the attraction between unlike molecules (such as water and a glass surface); the interplay of the two produces effects like capillary action and the curved meniscus seen in narrow tubes.
Key facts
| Field | Physical Chemistry |
|---|---|
| Main causes | Hydrogen bonding, dipole-dipole forces, van der Waals forces |
| Key related property | Surface tension |
| Contrasted with | Adhesion (attraction between unlike substances) |
A drop of water on a waxed car hood beads into a near-spherical shape because hydrogen-bonded cohesive forces between water molecules pull the surface inward, minimizing surface area rather than spreading out.
Frequently asked questions
What is the difference between cohesion and adhesion?
Cohesion is the attraction between molecules of the same substance, while adhesion is the attraction between molecules of different substances, such as water sticking to glass.
Why does water have such strong cohesion?
Water molecules form extensive hydrogen bonds with each other, a comparatively strong intermolecular force, which gives water high cohesion and a correspondingly high surface tension.