Water is polar, meaning that it has distinct ends with partial charges. The oxygen atom has a partial negative charge, while each hydrogen atom has a partial positive charge. Due to theses partial charges, the most stable arrangement for the molecule is that of a tetrahedron, in which the two negative and two positive charges are approximately equidistant from one another. The oxygen atom lies at the center of the tetrahedron, the hydrogen atoms occupy two of the apexes, and the partial negative charges occupy the other two apexes. Water, as a result of cohesion, has surface tension. Surface tension is a resistance of water molecules to stretch as they are held together by cohesion. At the air-water interface all of the hydrogen bonds in water face downward, causing the molecules of the water surface to cling together. It is adhesive to any surface with which it can form hydrogen bonds with, which is why substances containing polar molecules get "wet" when immersed in water, while those with nonpolar molecules do not. Another property of water is its high specific heat. Because of the many hydrogen bonds that water molecules form with one another, a large input of thermal energy is required to break these bonds before the individual water molecules can begin moving freely and so have a high specific heat. Specific heat is defined as the amount of heat that must be absorbed or lost by one gram of a substance to change its temperature by one degree Celsius. It measures the extent to which a substance resists changing its temperature when it absorbs or loses heat. Water has a specific heat of 1 calorie/gram/degree Celsius, twice that of most carbon compounds. Only ammonia, which is more polar than water and forms very strong hydrogen bonds, has a higher specific heat than water.
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Polarity is one of the most important properties of water. The polarity of water allows it to form hydrogen bonds.