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Hydrogen bonding is a type of attractive force occurring between water molecules. This is because water molecules are polar, meaning they have a partial positive charge on one side and a partial negative charge on the other. This polarity results in each water molecule being loosely attracted to its neighbors.

In water, each hydrogen atom is bonded to an oxygen atom. Due to the electronegativity difference between oxygen and hydrogen, the hydrogen ends up slightly positive. The oxygen side, however, becomes slightly negative. This causes nearby water molecules to be attracted to each other - the hydrogen of one connects loosely with the oxygen of another – forming hydrogen bonds.

This loosely attracts water molecules and gives rise to a 'skin' effect seen on water's surface – the surface tension. This tension lets small objects float and droplets to form. However, this bonding is easily disrupted by external factors such as temperature changes or the addition of other molecules like surfactants.

Surfactants are compounds that reduce the surface tension of a liquid, like soap in water. These molecules have a unique structure with two main components: a hydrophilic head and a hydrophobic tail.

- **Hydrophilic Head:** This part of the molecule readily interacts with water. "Hydrophilic" literally means "water-loving", so this end of the molecule easily bonds with water molecules.
- **Hydrophobic Tail:** "Hydrophobic" means "water-fearing" or "water-repelling." This part avoids water and prefers interaction with other non-polar molecules, like oils or the air.

When surfactants are added to water, their molecules arrange themselves at the surface with the hydrophilic heads in the water and the hydrophobic tails sticking out. This arrangement disrupts the hydrogen bonding between water molecules, effectively lowering the cohesive forces and thus the surface tension. Surfactants are widely used in detergents, shampoos, and other cleaning products as they enable liquids to spread and penetrate more evenly.

Cohesive forces are the intermolecular forces that hold the molecules of a substance together. In liquids like water, these forces are chiefly due to hydrogen bonds but can also include van der Waals interactions or other types of molecular attraction.

In the context of surface tension, cohesive forces among water molecules cause the surface to contract and minimize its area, making it difficult for objects to penetrate the surface. This is why water beads on surfaces and why you can sometimes see a water droplet balancing on the surface of a leaf.

When you introduce a surfactant like soap, these cohesive forces are disrupted. The surfactant molecules insert themselves between water molecules, weakening those internal attractions (cohesive forces). This reduction in cohesion decreases the surface tension, making the liquid spread out easier. This concept is crucial in various everyday applications, including cleaning, where lowering surface tension improves the ability to remove dirt and oil.