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Unit 4: The Hydrosphere Part 1: Structure of the Hydrosphere Part 2: Oceans Part 3: Water Quality Part 1: The Structure of the Hydrosphere Objectives: 1.Characteristics of Water 2.The Water Cycle 3.Reservoirs within the Hydrosphere 4.River Basins Properties of Water • Water has unique properties that impact the role it plays on the Earth. o Polarity o Cohesion o Adhesion o High surface tension o Density o High specific heat o High heat of vaporization The Water Molecule • Made of 2 H atoms and 1 O atom • The atoms share valence electrons to form covalent bonds. Water is Polar Covalent • However, the electrons are not shared equally. • Oxygen has a much stronger attraction for the electrons so the shared electrons get pulled closer to the oxygen. • This makes the oxygen slightly negative and the hydrogen atoms slightly positive. • This unequal sharing of electrons is called polarity. Water is Polar Covalent Partially negative Partially positive Most of the properties of water are due to polarity! Cohesion • Attraction of water molecules to each other. Surface Tension • Cohesion cause surface tension. Molecules on the surface have no neighbors above so they pull more strongly on those beside and below them. – This forms a surface "film" which makes it more difficult to move an object through the surface than to move it when it is underwater. – This also makes water form drops because the surface molecules are pulled inward. Surface Tension • Water attracts itself and pulls in to form a drop with a “film” on its surface. Adhesion • Attraction of water to an unlike substance Cohesion and Adhesion What forms a drop? • Cohesion causes water to form drops • surface tension causes them to be nearly spherical • adhesion keeps the drops in place. Interesting Polarity Facts • Polar substances stick to other polar substances. –Polar ↔ Polar = High Adhesion –Polar ↔ Nonpolar = Low Adhesion Water Drop Shapes • Water coheres to itself and forms a nice, round drop. • On a nonpolar surface the drop stays round (low adhesion) • On a polar surface the drop flattens out because polar water “sticks” to the polar surface. (higher adhesion) Capillary Action– water moves through narrow, porous spaces • Some of the molecules adhere to the surface of the object. • The other molecules that are cohered to them are pulled along. Adhesion to surface of object Cohesion of water to water Capillary action of absorbent paper Interesting Polarity Facts • “Like dissolves like” • Polar solvents dissolve polar substances. • Nonpolar solvents dissolve nonpolar substances • BUT Polar and Nonpolar don’t mix. • Water is called the universal solvent because so many things will dissolve in it. “Like Dissolves Like” • Oil and water do not mix. Oil is nonpolar Water is polar Density of Water • Cold water is more dense than water up to the freezing point. • So cold water sinks and warm water rises. • This happens in the oceans and regulates our climate. Density of Water • Solids are usually more dense than liquids. • Solid water (ice) is actually less dense then liquid water. • That means ice floats on water. – Important for lakes/ponds High Specific Heat of Water • Specific Heat (or heat capacity) is the amount of heat (i.e. thermal energy) needed to raise the temperature of a substance. • High Specific Heat = lots of heat to raise the temperature = takes longer • Low Specific Heat = little heat needed to raise the temperature = quicker High Specific Heat of Water • This means water can absorb a lot of heat without changing temperatures drastically. • Large bodies of water maintain a moderate temperature even when the air temperature changes drastically. High Heat of Vaporization • Heat of Vaporization: amount of heat needed to vaporize a liquid • This makes evaporation a cooling process. • Water has a high heat of vaporization which means that when water evaporates it takes a lot of heat with it. Water, Water Everywhere! • Water is one of the most common substances on the surface of the Earth. • Water covers about 71% of the planet – Exists as a solid (ice), liquid (water), or gas (vapor) • But less than 1% is drinkable Distribution of Water on Earth All Water Fresh Water Easily Accessible Fresh Water The Water Cycle • The total amount of water on Earth is constant. • But the water can move to different reservoirs and change phases. – A reservoir is a storage location for water (the atmosphere, oceans, lakes, glaciers, etc.) – Residence time is the amount of time that water stays in a given reservoir. • Energy from the sun drives the water cycle The Water Cycle infiltration Water Cycle • Go to http://www.hippocampus.org/Earth%20Science • Click on Environmental Science • Then choose Water Cycle Hydrosphere Reservoirs: Atmosphere • Contains water vapor • Average residence time = 10 days Hydrosphere Reservoirs: Ice • Frozen water is found in the polar ice caps, glaciers, and icebergs. • The oldest ice sample identified had an estimated residence time of 900,000 years Hydrosphere Reservoirs: Groundwater • Water that moves through the soil through the process of infiltration. Infiltration Water Table Saturated Zone (Permeable Layer) Impermeable Layer Hydrosphere Reservoirs: Groundwater An aquifer is an underground layer of waterbearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a well. Hydrosphere Reservoirs: Groundwater • Potential Threats to Groundwater – Overuse and depletion – Contamination – Improper wastewater management – Pharmaceutical and personal care products – Nitrates Hydrosphere Reservoirs: Groundwater Hard vs. Soft Water • Hard water contains dissolved minerals (like calcium and magnesium) – Tastes good, BUT it can be damaging to plumbing and soaps don’t lather well. • Soft water contains almost no dissolved minerals (except sodium). – If it is too soft, then it doesn’t taste as good, but it is easier on the plumbing and works better for washing. Hydrosphere Reservoirs: Lakes • Large bodies of surface water found on continents. Hydrosphere Reservoirs: Rivers & Streams • Account for a very small % of water, but are very important! • Carry water out to the ocean Hydrosphere Reservoirs: Wetlands • Areas of land that are covered with a shallow layer of water for at least part of the year • Marshes-grassy wetlands • Swamps-wetlands that have trees and bushes • Importance: – Recharge groundwater – Filter water – Habitat for many birds and animals Hydrosphere Reservoirs: Estuaries • The point where a river meets the ocean. • Contain a mix of fresh and salt water called brackish water. • Aquatic nurseries Hydrosphere Reservoirs: Oceans • Salty because water (the universal solvent) dissolves chemicals from the soil and deposits them in the oceans. • Volcanoes release solid and gaseous materials that contribute. • And hydrothermal vents on the ocean floor release superheated ocean water from the earth. Hydrosphere Reservoirs: Oceans • Oceans are critical to maintaining our climate • Oceans collect, mix, and circulate water, heat and carbon dioxide. – High Specific Heat, High Heat of Vaporization, and the unique density of water are critical in maintaining moderate temperatures on the Earth. Average Residence Times River Basins • River basins include the entire land surface drained by the various streams and creeks that flow downhill into one another, and eventually into one river. • The final destination of the water drained by a river basin is an estuary or an ocean. – A river basin sends all the water falling on the surrounding land into a central river and out to the sea. River Basins • Everyone lives in river basin. • Our actions will affect water quality far from our homes because the water will travel across the land, into a river, and out to the ocean. • Topography determines the river basin. – Water flows downhill!