Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area. The surface tension of a liquid results from an imbalance of intermolecular attractive forces, the cohesive forces between molecules:
A molecule in the bulk liquid experiences cohesive forces with other molecules in all directions.
A molecule at the surface of a liquid experiences only net inward cohesive forces.
Forces of attraction between a liquid and a solid surface are called adhesive forces. The difference in strength between cohesive forces and adhesive forces determine the behavior of a liquid in contact with a solid surface.
Water does not wet waxed surfaces because the cohesive forces within the drops are stronger than the adhesive forces between the drops and the wax.
Water wets glass and spreads out on it because the adhesive forces between the liquid and the glass are stronger than the cohesive forces within the water.

Surface Tension

Surface tension is a property of liquids that arises due to the cohesive forces between the molecules at the surface of the liquid. It is defined as the force per unit length acting perpendicular to the line drawn on the surface of the liquid. This force tends to minimize the surface area of the liquid.

The surface tension of water is primarily due to the strong hydrogen bonding between water molecules. Hydrogen bonding occurs when the slightly positive hydrogen atom of one water molecule is attracted to the slightly negative oxygen atom of another water molecule. This attraction creates a net force that holds the molecules together and gives rise to the cohesive properties of water.

Water molecules in the liquid phase

In the liquid phase, water molecules are in close proximity to each other and experience strong intermolecular forces of attraction. These forces, primarily hydrogen bonding, cause the water molecules to stick together and form a continuous network. The cohesive forces between water molecules are stronger than the attractive forces between water molecules and the surrounding gas molecules.

Water molecules in the gas phase

In the gas phase, water molecules are more spread out and have higher kinetic energy compared to the liquid phase. The attractive forces between water molecules in the gas phase are weaker than those in the liquid phase. Additionally, the attractive forces between water molecules and gas molecules in the surrounding environment are also weaker.

Surface tension and water molecules

Surface tension is a result of the imbalance of forces at the surface of a liquid. The water molecules in the bulk of the liquid are attracted to neighboring molecules from all directions, resulting in a net force of zero. However, at the surface of the liquid, the water molecules experience a net inward force due to the cohesive forces with the neighboring molecules.

This surface tension causes the liquid to behave as if it has a thin, flexible "skin" on its surface. This phenomenon can be observed in various everyday situations, such as the formation of droplets, the ability of insects to walk on water, and the capillary action in plants.

In conclusion, the attraction between water molecules in the liquid phase is stronger than the attraction between water molecules in the gas phase. This difference in attraction is responsible for the surface tension exhibited by water.