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1、STEMThermalExpansionofSeaWater—anExperiment(teachersguide—suggestedanswersinreditalics)BackgroundEachwatermoleculeincludesoneoxygenatomandtwohydrogenatomsthatshareelectronsincovalentbonds.Becauseoxygenatomshaveahigherelectronaffinitythanhydrogenatoms,theelectronsthatmo
2、vebackandforthbetweenthetwohydrogenatomsandtheoxygenatomspendmoretimeontheoxygenatomthanonthehydrogenatoms.Asaresult,theoxygenendsofwatermoleculeshaveaslightlynegativechargeandthehydrogenendshaveaslightlypositivecharge.Therefore,watermoleculesarereferredtoaspolarmolecu
3、les.Negativelychargedoxygenendsofwatermoleculesareattractedtohydrogenendsofdifferentwatermolecules.Theattractionbetweenwatermoleculesiscalledahydrogenbond.Hydrogenbondsaremucheasiertobreakthancovalentbondswithinwatermolecules.Evenso,hydrogenbondsareresponsibleformanyof
4、theunusualcharacteristicsofwater.Watermoleculeslosekineticenergyasthetemperaturedecreasestothefreezingpoint.Thehydrogenbondbetweenwatermoleculesorganizesiceintoahexagonalsolidstructure.Icehasafairlyopen(orlowdensity)structure.Whenicemelts,icestructureswillcollapseandth
5、ehydrogenbondsbetweenwatermoleculeswillpullthewatermoleculesclosertogetheruntilwaterreachesatemperatureof4oCelsius.Thatisthetemperaturewherewaterhasitsgreatestdensity.Asthetemperatureofliquidwaterrisesabove4oCelsius,thekineticenergyofthewatermoleculescontinuestoriseand
6、thehydrogenbondsbetweenwatermoleculesarenotabletopreventthewatermoleculesfrommovingapart.Asaresult,abodyofwillexpandasitstemperaturerisesabove4oCelsius.Supplies·25mlGraduatedcylinderthatcanwithstandheat.Graduationsshouldbe0.5mlor0.2ml·Refrigeratedwater(~15oC)·Corkwitha
7、holeinitthatfitssnuglyinthecylinder·Thermometer(fitssnuglyintothehole)·Potholders·GraphpaperorgraphingprogramFig.2.ExperimentSetupwww.umassk12.net/ipyASTEMEDProgramattheUniversityofMassachusetts,fundedbytheNationalScienceFoundationandsupportedbytheClimateSystemResearch
8、CenterinconjunctionwiththeInternationalPolarYearSTEMProcedurePerformthefollowingexperimentandrecordyourresultsinadata
