Water and Hydrogen Bonds Make Life Possible
The Importance of Hydrogen Bonding in Water Molecules:
Much of water's exceptional characteristics that create an amiable environment for the evolution and continuity of species are directly related to water's ability to form hydrogen bonds with itself. Because the oxygen atom in water is more electronegative than the two hydrogen atoms (this is related to the number of valence electrons in each respective valence shell), when the two elements combine they create a polar molecule. This polar molecule consists of a negatively charged oxygen atom and two positively charged hydrogen atoms; again, this phenomenon is related to the fact that oxygen has more valence electrons than hydrogen. When water molecules come in close proximity to each other they form hydrogen bonds--bonds between the negatively charged oxygen and positively charged hydrogen. This fundamental property of water accounts for its cohesive properties, ability to moderate temperature, and ability to act as a solvent.
Water's Cohesive Properties:
The hydrogen bonding of water, as one would expect, creates an attraction between individual molecules. Thus, water molecules stay relatively close together--this phenomenon is known as cohesion. Cohesion is essential to life processes on earth. Without cohesion, plants would be doomed by gravity as water has to move up against the force of gravity through the stem to the chloroplasts. If water did not form bonds with itself, their would be no force to counteract the effect of gravity to pull the molecules apart. More directly, cohesion (and surface tension) relate the ability of water striders movement across bodies of water. Cohesion, made possible by hydrogen bonding, plays an extremely important role in the processes of life.
How Does Water Moderate Temperatures?
Perhaps more important, however, is water's ability to moderate temperatures. Because water can form hydrogen bonds, it has a high specific heat and heat of vaporization. The former relates a substance's ability to resist changes in temperature; more specifically, the amount of energy it takes to raise the temperature of 1 gram of water by 1 degree Celsius (or the amount of energy to reduce the temperature by the same amount). The latter relates a substance's ability to resist vaporization, and is specifically defined as the amount of heat a substance has to absorb in order for one gram to change from a liquid to a gas. Because water has such a high specific heat, it moderates coastal temperatures by absorbing heat during the day and releasing it during the night--creating a more suitable environment for life. Moreover, the oceans, consisting of water, are moderated by the properties of water and its high specific heat. The heat of vaporization of water, which is likewise high, is related to water's ability to form hydrogen bonds and enables certain moderation processes in biology. In humans, for example,sweat glands capitalize on the high heat of vaporization of water by secreting water onto the surface of the skin in order to lower body temperatures.
Water as a Universal Solvent:
Finally, water, sometimes called the worlds universal solvent, can dissolve solutes of numerous forms. Once again, tied to water's ability to form hydrogen bonds, water reacts with particles (forming hydrogen bonds). Even non-polar molecules such as sugar will dissolve in water, as water surrounds each individual molecule forming a hydration shell. Water's versatility when it comes to dissolving molecules has enormous implications for life and life processes. The fluids and nutrients in our blood, the sap in plants and trees, and many other important biological solutions are made possible by water and its unique properties as a solvent.
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