Presentation on theme: "Water Properties of water Polar molecule"— Presentation transcript:
1Water Properties of water Polar molecule Hydrogen bonds with other water moleculesThis is the foundation for all the properties of water
2WaterWater is the solvent, the medium and the participant in most of the chemical reactions occurring in the environment.On earth, water is found as a liquid, as a solid (ice) or as a gas (water vapor).Water molecules are attracted to each other, creating hydrogen bonds.These strong bonds determine almost every physical property of water and many of its chemical properties.
4Cohesion Water molecules stick to each other. The attraction between the water molecules is greater than the attraction between water and air.Creates a surface tension (film)Permits water to hold up substances heavier and denser than itself.Steel needle carefully placed on the surface of a glass of water will float.
5Cohesion of water molecules permits the flow of water in streams and rivers. Surface tension is essential for the transfer of energy from wind to water to create waves which are necessary for rapid oxygen diffusion in lakes and seas.Some aquatic insects such as this water strider (predators on smaller invertebrates) rely on surface tension to walk on water.
6AdhesionWater molecules bind to many other substances such as glass, cotton, plant tissues, and soils.For example, in a thin glass tube, when the molecules at the edge reach for and adhere to the molecules of glass just above them, they tow other water molecules along with them due to cohesion. The water surface, in turn, pulls the entire body of water to a new level until the downward force of gravity is too great to be overcome. This process is called capillary action.
7AdhesionAdhesion allows the flow of water through the vascular tissues of plants and the flow of blood through blood vessels.
8Adhesion Adhesion also produces viscosity Water flows in layers Laminar viscosity: friction between layersFlow is fastest in middleSlowest near edges of stream and bottom due to friction of layers
10Laminar viscosity: friction between layers of water Laminar viscosity: friction between layers of water. Flow is fastest in middle, and slowest near edges of stream and bottom due to friction between layers.
11Eddy viscosity: mixing of layers creates turbulence which keeps small organisms suspended in water column
12Plankton swirling in the turbulent flow of an ocean eddy
13Water’s High Specific Heat The specific heat is the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by 1oCTherefore, the specific heat of water is defined as:calorie/gram °C = joule/gram4.184 Joules = 1.00 calorieHighest of any common substance
14How Water Stabilizes Temperature Water’s high specific heat is linked to hydrogen bonding.Much of the heat energy is used to disrupt the hydrogen bonds before the water molecules can begin moving faster.When the temperature of the water drops slightly, many hydrogen bonds form, releasing a considerable amount of energy in the form of heat.
15High Heat CapacityWater absorbs or releases more heat than many substances for each degree of temperature increase or decrease.Warms slowlyCools slowlyEvaporative cooling: sweating, evapo-transpiration in plants
16High Heat CapacityDifferences in temperature between lakes and rivers and the surrounding air may have a variety of effects.Local fog or mist is likely to occur if a lake cools the surrounding air enough to cause saturation; small water droplets are suspended in the air.
17High Heat CapacityWater vapor forms a kind of global "blanket" which helps to keep the earth warm.Heat radiated from the sun-warmed surface of the earth is absorbed and held by the vapor.Water vapor contributes to global warmingIs it a greenhouse gas?
18High Heat CapacityLarge bodies of water, such as the oceans or the Great Lakes, have a profound influence on climate.Heat reservoirs and heat exchangersSources of moisture that falls as rain and snow over adjacent land masses.When water is colder than the air, precipitation is curbed, winds are reduced, and fog banks are formed.
19Freezing and BoilingPure water at sea level boils at 100°C and freezes at 0°C. At higher elevations (lower atmospheric pressures) water's boiling temperature decreases.Takes longer to boil an egg at higher altitudesDoesn’t get high enough to cook the egg properlyIf a substance is dissolved in water, the freezing point is lowered.Spread salt on streets in winter to prevent ice formation.
20Biological Antifreeze Must prevent formation of ice crystals inside cells.Insects cells replace water with glycerolPlants use sugars and proteins to increase solutes in the cytoplasmAntarctic fish use glycoproteins
21Water Vapor Absolute humidity: actual mass of water vapor in the air Relative humidity: % of max. water vapor for a particular temperatureDew point: saturation point for a particular temperature
22Air Temp. and Humidity Warm air holds more water vapor than cold air. This explains why indoor air is so dry in winter.Cold air outside holds little water.Air coming into house is dry.Heating dries it further.
24Dew Point If air can no longer hold water vapor without condensing, it is saturatedhas a relative humidity of 100%has reached its dew point temperature
25Dew PointThe temperature at which the air is completely saturated with water (i.e., RH = 100%).At this temperature water precipitates (goes from gas to liquid or solid) and forms clouds (and dew on grass and ice tea glasses) and potentially rains/snows.The dew point is given to indicate the amount of moisture in the air (specific humidity).
27Dew PointThe current dew point will never be higher then the current temperature.If the temperature is at the dew point and the temperature falls, the dew point must follow.The higher the dew point temperature, the more moisture there is in the air.Example: Death Valley(desert) California has low dew points, thus feels dry.Key West Fl. has high dew points, thus feels sticky.
28Universal SolventAn important property of water is its ability to dissolve other substances.Were it not for the solvent property of water, life could not exist because water transfers nutrients vital to life in animals and plants.A drop of rain water falling through the air dissolves atmospheric gases. When rain reaches the earth, it affects the quality of the land, lakes and rivers.Acid rain
32Selection for Life on Land Water is a stable environmentThe invasion of the land is really the invasion of the airAdaptations are really adaptations for life in the relatively drier atmosphere
33Selection for Life on Land What problems would have to be overcome?Desiccation: drying outWater for reproduction:Free water needed for gamete fusionProtection of embryo/prevent desiccationSupport:Can’t depend on water for buoyancyDispersal of offspring to colonize new habitatsCan’t depend on currents or swimming
36Chicago’s WeatherThere are two geographical factors that contribute to Chicago's weather.Lake Michigan: 450 miles long, 80 miles wide, 900 feet deep.Location: there really aren’t any major geographical features to the west or south of Chicago for nearly a thousand miles (1600 kilometers).
37Location effectOnce weather events start heading to Chicago, there is nothing in the geography to stop them.This means that there are usually two to three days warning before any major weather systems hit Chicago.This also means that any weather system that happens to head to Chicago tends to get there.This makes Chicago weather very variable in the long term.But it also tends to be predictable in the short term.
38Lake effectAs any huge mass of water does, Lake Michigan makes a dandy thermal mass.It tends to be much warmer that the air over it in winter, and much cooler than the air in summer.In winter, this bring lake effect snows that can drop six inches of snow on downtown while leaving the suburbs dry.In summer, this brings the lake breeze, which can drop the temperature dramatically downtown, while it’s broiling hot in the western ‘burbs.
40This also explains why NW Indiana, SE Michigan, and Buffalo, N. Y This also explains why NW Indiana, SE Michigan, and Buffalo, N.Y. are hit so hard by snowstorms in the winter.As air passes over the warm lake water, it picks up moisture.Then as it passes over the land, it cools and drops its moisture in the form of snow.