2What is water? Water is H2O One molecule of oxygen and two molecules ofhydrogen.
3But notice that the two hydrogen atoms are not on opposite sides of the oxygen. They are bunched together on the same side.This means that oneend of the moleculeis different than theother end.
4The oxygen end of the molecule has a negative charge and....................... the hydrogen endhas a positivecharge.This makes watera POLAR molecule.One pole is positiveand the other isnegative.
5Water is cohesive. It sticks to itself. Because opposites attract, the positive end of one water molecule is attracted to the negative end of any nearby water molecule.That’s why waterdroplets stick toone another.Water is cohesive. It sticks to itself.
7Other molecules may also be polar so water molecules stick to them....
8Some molecules are non-polar. Non-polar molecules won’tmix with water.That’s why oil and waterwill separate even if youtry to mix them together.
9Water does a very strange thing. It expands when it freezes at 0° C.Because it expands it gets less dense.Because it gets less dense, ice floats!Because ice floats there are ice burgs!Chasing Ice
10What would happen to lakes in the winter if water didn’t expend when it freezes? How would life on Earth be different?In winter the air gets cold.The water at the surface, incontact with this air freezes.Because the ice is less densethan the water below it floatson the surface.Since ice is a good insulator itprotects the lake water belowfrom the cold air.The lake never freezes solid. Life in the lake survives the winter.
11If water didn’t expand when it froze, ice would be more dense and would sink. More water at thesurface would freezeand sink until......
12The lake would freeze solid And everything inthe lake would die.
13Water has been called the UNIVERSAL SOLVENT. What is a solvent?A solvent is a material, usually a liquid, in whichother materials dissolve.If you want to clean adirty paint brush youbuy a paint solventthat dissolves the oldpaint.
14Water dissolves so many different substances that it is called the universal solvent. YOU are a big, walkingsolution of trillions ofmolecules all dissolvedin water!That’s why
15Astronomers who are searching the universe for alien life forms always say FOLLOW THE WATER!!!
17Water dissolves substances as it flows over and through the land on its way to the sea. Any soluble solublesubstance, such assalt, will be dissolvedand will end up inthe ocean.This is why the seasare salty.
18Does that mean that the oceans used to be less salty than they are today? YES!!!
19Why does the salt accumulate in the oceans? Water can evaporate leaving the salt behind orWater can freeze leaving the salt behindThe only way salt can leave the ocean is ifthe entire ocean evaporates
20What else is dissolved in sea water besides salt? Lots of things like gypsum which is used to makewallboard and plaster,and calcium carbonate which forms limestone,chalk, and marble.
21How does limestone and chalk form? Clams, oysters, and other organisms extract thecalcium carbonate from the seawater to maketheir shells. When they die their shells pile upand form limestone which may become marble.
22Who cares? Limestone and marble are mined for commercial use but more important is the billions of tons ofcarbon that remains in the oceans and does notget into the air where it would cause globalwarming on a MASSIVE scale.
23Specific Heat Water has the highest specific heat of any common substance.Specific heat refers to the amount of energywater needs to absorb before it changestemperature.It takes a LOT of heat energy to heat water sowater heats up and cools down VERY SLOWLY
24What difference does the specific heat of water make in my wonderful and exciting life? Locations nearthe oceans havecooler summersand warmerwinters thaninland locations.
25Large bodies of water eliminate extremes of temperature! This affectsthe growingseason and whatcrops can begrown in a region.
26Water has Surface Tension Surface tension is the tendency of the surfaceof a liquid that allows it to resist an external force.Remember that water molecules are cohesive.....they stick together.The water molecules IN theliquid are attracted equally inevery direction so all the forcesacting on them cancel eachout.
27But the forces acting on the molecules on the surface areunequal.Surface molecules are pulledinward towards the center.This creates a force, or tensionThis tension pulls the waterinto a spherical shape ordroplet.
28Water striders are insects that can walk on water. They can do this because their mass is distributedover a wide area and because their legs are non-polar. They repell water.The force of gravity is less than the force needed to break thesurface tension.
29Water shows Capillarity (aka capillary action) Capillarity is the movement of water moleculesdue to the attraction of those molecules to thesurface they are on.Remember, water molecules arepolar. One end of a molecule ispositive, the other negative.These charges are attractedto charges on a surface such asa tube which pulls the water up.
30The attraction between water molecules andpaper fibers pulls thewater up and into thepaper.Capillarity in the xylem tubesof plants helps to explain howplants can “pull” water upto their leaves against theforce of gravity.
31If water didn’t have this property the tallest plant on Earth would be only a few inches tall and giant sequoias (aswell as all othertrees)....wouldn’t exist
32Gases dissolve in water! This includes oxygen (not to be confused with theoxygen that is part of the water molecule).Dissolved oxygen can be easily extracted!Fish do it all day long.So could you if you hadgills.
33Carbon dioxide (CO2 ) also dissolves in water. When carbon dioxide dissolves in water it formsCarbonic Acid, H2CO3You are probably more familiar with carbonicacid as seltzer or club soda. It is a very weakacid but it does react withCalcium carbonate which forms limestone,marble, and chalk.
34CAVES Since all rainwater contains dissolved carbon dioxide, all rainwater is really a weak acid.When the carbonic acid rain reacts with lime-stone it converts the limestone to carbondioxide (bad for global warming) and createsCAVES
35So what is so special about water? 1) It is polar and because it’s polar it......2) Dissolves other substances such as salt, andcalcium carbonate.3) Has surface tension which results in capillarity.4) Gases, including oxygen, dissolve in water.5) It dissolves CO2 forming carbonic acid.6) It has a high specific heat which means itchanges temperature, up or down, very slowly.
36How would YOUR life be different if any of these properties changed? 7) It expands when it freezes so that ice is lessdense than liquid water.8) When it evaporates or freezes the substancesthat may be dissolved in it, salt for example,remain behind.9) In its solid form, ice, it is a very good insulator.How would YOUR life be differentif any of these properties changed?