GEO-SCI 103Exam # 2 Study Guide Lectures: 6-10Lecture 6-10Water Properties:Why is water so unique? Water behaves differently from almost any other chemical compound that exists naturally. Differences begin with the basic arrangement of the atoms ina water molecule, as the molecule has an uneven distribution of electrical charge, which results in its asymmetrical shape. Dipolar structure of water moleculeThe uneven distribution of electrical charge results in an asymmetrical shape of the water molecule:1. The hydrogen side of the molecule (H2) has a net positive charge, and the Oxygen side (O) has a net negative charge. 2. This occurs because the negatively charged electrons spend more time in the vicinity of the O atom.What are hydrogen bonds? (why do they form and why are they important in understanding the unique properties of water? Why are they important in moving heat around the planet?Hydrogen Bonds: Because of this asymmetrical distribution of electrical charge in the water molecule, the positively charged ends of the water molecules are attracted to the negatively charged ends of adjacent molecules called hydrogen bonds. Hydrogen Bonds are important in understanding the unique properties of water because the degree of Hydrogen DETERMINES THE 3 PHASES OF WATERUnique Properties of Water:1. Water has a unique response of density to temperatureas water cools, hydrogen bonds begin to form that push the water molecules apart and cause the density to decrease. When water freezes, hydrogen bonds in the ice form a hexagonal crystalline structure that pushes the molecules even further apart. This lowers the density of ice below that of liquid water and results in ice floating (As water cools, hydrogen bonds push apart water molecules which lowers the density)2. Water has high boiling and freezing points In water, hydrogen bonds must be broken or formed to boil or freeze the liquid. For this to occur, it requires high temperatures (more heat) compared to other molecules that don’t have hydrogen bonds.3. Water has high heat capacity water absorbs and releases a considerableamount of heat with little change in temperature. Water’s high heat capacityhelps to moderate surface temperatures on Earth4. Water has high latent heat of vaporization and high latent heat of fusion3 naturally occurring phases (states)1. Solid (Ice)crystalline structure is less dense than liquid water2. Liquid (water)liquid water is more dense than ice3. Gas (water vapor)high energy molecules with few H bonds Differences between sensible heat and latent heat (latent heat of vaporization, latent heat of fusion)Sensible Heat Latent heatEnergy required to change the temperature of a substance with no phase changeHeat needed to change water from one phase to another; occurs without a change in temperature because the energy gained (or lost) is used to break (or form) hydrogen bondsExamples: ice warming, water heating, water cooling, steam superheating, steam super coolingHigh Latent heat of vaporization: amount of heat required to change water into steam (540 cal/g) High Latent Heat of Fusion: amount of heat needed to melt iceCalorie: amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius Moves moisture and heat around the planet (thunderstorms, hurricanes)Few examples of latent heatLatent Heat of Fusion ice melting, water freezing Latent Heat of Vaporization water boiling, steam condensingHydrologic Cycle:What happens during evaporation and precipitation?Evaporation—water at the surface of the ocean will absorb energy from the sun and evaporate into the atmosphere. Will remove 540 calories of heat from the ocean and carry it in the atmosphere with the water vaporCondensation when the water vapor cools in the upper parts of the atmosphere it can condense into clouds and raindrops, releasing the latent heat from the water vapor into the atmosphere. Precipitation Condensed Water vapor that falls to the Earth’s Surface (rain, snow, hail, sleet)Transpiration Process by which plants release water vapor as a byproduct of photosynthesis RunofVariety of ways water moves across the land: Includes both surface (streams and rivers) with subsurface (groundwater) flow of liquid water toward the ocean under the influence of gravity or hydrostatic pressure.Why is latent heat important in making Earth a habitable place to live?Ocean SalinityWhy is seawater salty?Most of the oceans salts were derived from the gradual processes such as the old breaking up of the cooled igneous rocks of the Earth’s crust by weathering and erosion, the wearing down of mountains, and the dissolving action of rains and steams that transported mineral washings to sea - Chemical weathering of rocks transportation to the ocean by wind and runoff from the land- Volcanic emissions - Hydrothermal activity on the seafloorionic exchange between superheated seawater and oceanic crust (basalt) at the spreading centers- Fluid flow out of accretionary prisms (above deep-sea trenches)What are salts? (Anions and cations)The dipolar nature of the water molecule has dissociated the bonds between these substances leaving them with either a positive charge or negative chargePositively charged ions are called cations Negatively charged ions are called anionsDefinition of salinity Refers to the total dissolved solids in water, and these are mostly the ions on mineral salts such as sodium chloride (NaCl). Units of salinity Oceanographers describe salinity with units of parts per thousand (%, ie grams of dissolved solids per kilogram of water, g/kg)Average and range of ocean salinityAverage ocean Salinity is approximately 35% and in most parts of the ocean, salinity ranges between 33%-37%Where do dissolved ionscome from?Chemical Weathering the natural breakdown of rocks and soils on land. Theions are then transported to the ocean by rivers (runoff)What are the six most common dissolved ions in seawater?1.Chloride (anion that accounts for 55.1% by weight of the ocean’s salinity2.Sodium (cation that accounts for 30.6% of ocean’s salinity)**These two ions combine when the seawater is evaporated to form NaCl,sodium chloride, which is a common table salt**3.Sulfate (7.7%)4.Magnesium (3.7%)5.Calcium (1.2 %)6.Potassium (1.1 %)Why doesn’t the ocean become more salty overtime?The chemical composition of the ocean has remained relatively constant overtime because chemicals ENTER the