2Properties of Water Polar molecule Cohesion and adhesion High specific heatDensity – greatest at 4oCUniversal solvent of life
3Polarity of WaterIn a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Gives water more structure than other liquidsBecause oxygen is more electronegative, the region around oxygen has a partial negative charge.The region near the two hydrogen atoms has a partial positive charge.A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.2 corners are orbitals with unshared electrons and a weak negative charge2 are occupied by hydrogen atoms that have polar covalent bonds
4HYDROGEN BONDSExtraordinary Properties that are a result of hydrogen bonds.Cohesive behaviorResists changes in temperatureHigh heat of vaporizationExpands when it freezesVersatile solventHold water molecules togetherEach water molecule can form a maximum of 4 hydrogen bondsThe hydrogen bonds joining water molecules are weak, about 1/20th as strong as covalent bonds.They form, break, and reform with great frequency
6Organisms Depend on Cohesion Hydrogen bonds hold the substance together, a phenomenon called cohesionCohesion is responsible for the transport of the water column in plantsCohesion among water molecules plays a key role in the transport of water against gravity in plantsAdhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.
7Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface.Water behaves as if covered by an invisible film.Some animals can stand, walk, or run on water without breaking the surface.Fig. 3.3
8High Specific Heat Moderates Temperatures on Earth Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.Celsius Scale at Sea Level100oCWater boils37oCHuman body temperature23oCRoom temperature0oCWater freezes
9Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1oC.Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for:Prevention of temperature fluctuations that are outside the range suitable for life.Coastal areas having a mild climateA stable marine environment
10Evaporative CoolingThe cooling of a surface occurs when the liquid evaporatesThis is responsible for:Moderating earth’s climateStabilizes temperature in aquatic ecosystemsPreventing organisms from overheating
11Density of Water Most dense at 4oC Contracts until 4oC Expands from 4oC to 0oCThe density of water:Prevents water from freezing from the bottom up.Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation.Makes transition between season less abrupt.
13Solvent for Life Solution Aqueous solution Hydrophilic Hydrophobic SolutesolventAqueous solutionHydrophilicIonic compounds dissolve in waterPolar molecules (generally) are water solubleHydrophobicNonpolar compounds
14Solvent for Life Because of its high polarity, water is called the universal solvent. A solvent is a substance that dissolves, or breaks apart, another substance (known as a solute). A general rule that determines whether a substance will dissolve in a solvent depends upon its polarity. Polar solvents dissolve polar solutesnonpolar solvents dissolve nonpolar solutes.
15Water Hardnesshardness-a water-quality indication of the concentration of alkaline salts in water, mainly calcium and magnesium. If the water you use is "hard" then more soap, detergent or shampoo is necessary to raise a lather.
16Acid PrecipitationRain, snow or fog with more strongly acidic than pH of 5.6West Virginia has recorded 1.5East Tennessee reported 4.2 in 2000Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphereLowers pH of soil which affects mineral solubility – decline of forestsLower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.