Why does WATER have a high SURFACE TENSION?
Not only water has a high surface tension, but all liquids. Explanation follows.
Consider a water molecule situated on the first layer of molecules just at the surface of the liquid. This molecule interacts with its neighbours. Above there are air molecules, below thare are water molecules. Consider that the force of interaction with one molecule of air is approx. equal to the force of interaction with one molecule of water. Now, because the density of air is about 1.22 kg/m^3 and the density of water is about 1000 kg/m^3 it means the number of water molecules in the water (below the molecule considered at the surface) is 1000 times bigger than the number of air molecules (above the molecule considered the surface). This means that the total interaction force of this surface molecule of water with air is 1000 times lesser than the interaction force with the water. This unbalanced force (of the interaction of ALL surface molecules with the water molecules below them) form is called SURFACE TENSION.
Water has high surface tension due to its polarity and hydrogen bonds. This is due to cohesion. Cohesion are water molecules ability to stick together.
Water's high surface tension is an important aspect of biology. Water striders (small insects) can safely "ski" across the surface of water because it is hard to break water's surface.
Water has high surface tension. Water, however, expands considerably when it freezes. This remarkable quality is due to the linkage between molecules because of hydrogen bonding. As the temperature becomes lower, and the molecules become more sluggish, there will be more and more hydrogen bonding. The expansion of water as it freezes has various important consequences. For one thing, the water that makes its way between cracks in rock expands upon freezing and exerts great pressure. This gradually causes fragments of rock to break off. Thus freezing water becomes an effective erosive agent.