BIOL-L 112 1nd Edition Lecture 1 Outline of Current Lecture I. Water’s Role in LifeA. Electronegativity and the Difference Between Polar and Nonpolar MoleculesII. Water’s Ability to Form Hydrogen BondsIII. Two of the Four Emergent Properties of WaterCurrent LectureI. Water plays a crucial role in life processes. Water is unique because of the way it exists as a solid, liquid, and gas in the natural environment. Organisms need this molecule more than any other substance in order to survive. - Example: In the arctic, water exists as a liquid in the ocean, a solid as ice, and a gas aswater vapor in the sky. A. Water is a highly polar molecule. Because the oxygen atom is more electronegative that the hydrogen atoms, the electrons are pulled towards oxygen. This creates a partial negative on oxygen and a partial positive on both hydrogen atoms. Electronegativity is a calculated value that describes the ability of an atom to attract electrons towards itself. As a general rule, electronegativity increases across the rows in the periodic table.o Non-polar molecules share electrons equally between a covalent bond because the atoms do not have much of a difference in electronegativity. They are usually symmetrical. Examples: CH4, O2o Polar molecules do not share covalent bonds equally, creating partial positive and partial negative charges. They are usually asymmetrical. Examples: H2O, NH3II. Because of the polarity of water, it is able to form hydrogen bonds with four other water molecules. The two partial positive charges on hydrogen form a hydrogen bond with the oxygen atoms in two different water molecules, while the oxygen is able to form two hydrogen bonds with two different hydrogen molecules. - Hydrogen bonds are much weaker than covalent bonds, and constantly break and reform quickly with different water molecules.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Hydrogen bonding allows water to have four unique properties. First, it has cohesive behavior because the hydrogen bonds hold molecules of water together. Water cohesively clings to itself, and adhesively clings to other polar molecules. Because of this, water can travel against the force of gravity. This is extremelyimportant in transporting water and nutrients upwards in plants. Second, water is able to moderate temperature. This is because water has a very high specific heat (1 cal/g°C). Water releases stored heat to the air that is cooler, and absorbs heat from the air that is warmer. Due to the amount of heat needed to break hydrogen bonds, water has a high heat of fusion (converting from a solid to a liquid at melting point) and heat of vaporization (converting from a liquid to a gas at boiling point). These high heats of fusion and vaporization makes water very stable as a liquid and also minimizes temperature fluctuations. Minimal temperature fluctuations play a key role in permitting life. The high heat of vaporization has both pros and cons. A pro is evaporative cooling, which cools down the surface of a liquid as the molecules of water are converted into water vapor. A con is the severity of steam burns on skin, which are caused by the large amount of heat that is released from steam as it turns into a liquid. Definitions: - Heat (“Thermal Energy”): The total amount of kinetic energy in a body of matter and depends on volume. - Temperature: Not a type of energy, but a measure in degrees reflecting the average kinetic energy of molecules using a thermometer. - Specific Heat: The amount of heat absorbed or lost when 1 gram of a substance changes its temperature by