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Types Of Bonds

HEMISTRY II: WATER AND ORGANIC MOLECULES
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It can be quite correctly argued that life exists on Earth because of the abundant liquid water. Other planets have water, but they either have it as a gas (Venus) or ice (Mars). This relationship is shown in Figure 1. Recent studies of Mars reveal the presence sometime in the past of running fluid, possibly water. The chemical nature of water is thus one we must examine as it permeates living systems: water is a universal solvent, and can be too much of a good thing for some cells to deal with.
Figure 1. Water can exist in all three states of matter on Earth, while only in one state on our two nearest neighboring planets. The above graph is from http://www.crseo.ucsb.edu/IOM2/Triple_Point.html.



Water is polar covalently bonded within the molecule. This unequal sharing of the electrons results in a slightly positive and a slightly negative side of the molecule. Other molecules, such as Ethane, are nonpolar, having neither a positive nor a negative side, as shown in Figure 2.
Figure 2. The difference between a polar (water) and nonpolar (ethane) molecule is due to the unequal sharing of electrons within the polar molecule. Nonpolar molecules have electrons equally shared within their covalent bonds. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.


These link up by the hydrogen bond discussed earlier. Consequently, water has a great interconnectivity of individual molecules, which is caused by the individually weak hydrogen bonds, shown in Figure 3, that can be quite strong when taken by the billions.
Figure 3. Formation of a hydrogen bond between the hydrogen side of one water molecule and the oxygen side of another water molecule. Image from...