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Unformatted text preview: CHAPTER 3 WATER AND T HE F I TNESS OF T HE ENV IRON MENT Water's extraordinary properties are emergent properties resulting from water's structure and molecular interactions. I. Water's Polarity and I ts Effects A. The polarity of water molecules results in hydrogen bonding Water is a polar molecule. I ts polar bonds and asymmetrical shape give water molecules opposite charges on opposite sides. - Four valence orbitals of O point to corners of a tetrahedron. -Two corners are orbitals with unshared pairs of electrons and weak negative charge. -Two corners are occupied by H atoms which are in polar covalent bonds with O. Oxygen is so electronegative, that a H shared electrons spend more time around the O causing a weak positive charge near H's. Hydrogen bonding orders water into a higher level of structural organization. -The polar molecules of water are held together by hydrogen bonds. -Positively charged H of one molecule is attracted to the negatively charged O of another water molecule. Water has extraordinary properties that emerge as a consequence of its polarity and hydrogen-bonding. Some of these properties are that water: - has cohesive behavior - resists changes in temperature - has a high heat of vaporization and cools surfaces as it evaporates - expands when it freezes - is a versatile solvent B. Organisms depend on the cohesion of water molecules. Cohesion = Phenomenon of a substance being held together by hydrogen bonds. -Though hydrogen bonds are transient, enough water molecules are hydrogen bonded at any given time to give water more structure than other liquids. -Contributes to upward water transport in plants by than other liquids....
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This note was uploaded on 08/12/2008 for the course BIOL 101 taught by Professor Hogan during the Fall '08 term at UNC.
- Fall '08