化学专业英语电子版.docx
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化学专业英语电子版.docx
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化学专业英语电子版
Chapter1MatterandMeasurement
Chemistryisthescienceofmatterandthechangesitundergoes.Chemistsstudythecomposition,structure,andpropertiesofmatter.Theyobservethechangesthatmatterundergoesandmeasuretheenergythatisproducedorconsumedduringthesechanges.Chemistryprovidesanunderstandingofmanynaturaleventsandhasledtothesynthesisofnewformsofmatterthathavegreatlyaffectedthewaywelive.
Disciplineswithinchemistryaretraditionallygroupedbythetypeofmatterbeingstudiedorthekindofstudy.Theseincludeinorganicchemistry,organicchemistry,physicalchemistry,analyticalchemistry,polymerchemistry,biochemistry,andmanymorespecializeddisciplines,e.g.radiochemistry,theoreticalchemistry.
Chemistryisoftencalled"thecentralscience"becauseitconnectstheothernaturalsciencessuchasastronomy,physics,materialscience,biologyandgeology.
1.1.ClassificationofMatter
Matterisusuallydefinedasanythingthathasmassandoccupiesspace.Massistheamountofmatterinanobject.Themassofanobjectdoesnotchange.Thevolumeofanobjectishowmuchspacetheobjecttakesup.
Allthedifferentformsofmatterinourworldfallintotwoprincipalcategories:
(1)puresubstancesand
(2)mixtures.Apuresubstancecanalsobedefinedasaformofmatterthathasbothdefinitecompositionanddistinctproperties.Puresubstancesaresubdividedintotwogroups:
elementsandcompounds.Anelementisthesimplestkindofmaterialwithuniquephysicalandchemicalproperties;itcannotbebrokendownintoanythingsimplerbyeitherphysicalorchemicalmeans.Acompoundisapuresubstancethatconsistsoftwoormoreelementslinkedtogetherincharacteristicanddefiniteproportions;itcanbedecomposedbyachemicalchangeintosimplersubstanceswithafixedmassratio.Mixturescontaintwoormorechemicalsubstancesinvariableproportionsinwhichthepuresubstancesretaintheirchemicalidentities.Inprinciple,theycanbeseparatedintothecomponentsubstancesbyphysicalmeans,involvingphysicalchanges.Asampleishomogeneousifitalwayshasthesamecomposition,nomatterwhatpartofthesampleisexamined.Pureelementsandpurechemicalcompoundsarehomogeneous.Mixturescanbehomogeneous,too;inahomogeneousmixturetheconstituentsaredistributeduniformlyandthecompositionandappearanceofthemixtureareuniformthroughout.Asolutionsisaspecialtypeofhomogeneousmixture.Aheterogeneousmixturehasphysicallydistinctpartswithdifferentproperties.Theclassificationofmatterissummarizedinthediagrambelow:
Mattercanalsobecategorizedintofourdistinctphases:
solid,liquid,gas,andplasma.Thesolidphaseofmatterhastheatomspackedcloselytogether.Anobjectthatissolidhasadefiniteshapeandvolumethatcannotbechangedeasily.Theliquidphaseofmatterhastheatomspackedcloselytogether,buttheyflowfreelyaroundeachother.Matterthatisliquidhasadefinitevolumebutchangesshapequiteeasily.Solidsandliquidsaretermedcondensedphasesbecauseoftheirwell-definedvolumes.Thegasphaseofmatterhastheatomslooselyarrangedsotheycantravelinandouteasily.Agashasneitherspecificshapenorconstantvolume.Theplasmaphaseofmatterhastheatomsexistinginanexcitedstate.
1.2.PropertiesofMatter
Allsubstanceshaveproperties,thecharacteristicsthatgiveeachsubstanceitsuniqueidentity.Welearnaboutmatterbyobservingitsproperties.Toidentifyasubstance,chemistsobservetwodistincttypesofproperties,physicalandchemical,whicharecloselyrelatedtotwotypesofchangethatmatterundergoes.
Physicalpropertiesarethosethatasubstanceshowsbyitself,withoutchangingintoorinteractingwithanothersubstance.Somephysicalpropertiesarecolor,smell,temperature,boilingpoint,electricalconductivity,anddensity.Aphysicalchangeisachangethatdoesnotalterthechemicalidentityofthematter.Aphysicalchangeresultsindifferentphysicalproperties.Forexample,whenicemelts,severalphysicalpropertieshavechanged,suchashardness,density,andabilitytoflow.Butthesamplehasnotchangeditscomposition:
itisstillwater.
Chemicalpropertiesarethosethatdochangethechemicalnatureofmatter.Achemicalchange,alsocalledachemicalreaction,isachangethatdoesalterthechemicalidentityofthesubstance.Itoccurswhenasubstance(orsubstances)isconvertedintoadifferentsubstance(orsubstances).Forexample,whenhydrogenburnsinair,itundergoesachemicalchangebecauseitcombineswithoxygentoformwater.
SeparationofMixtures
Theseparationofmixturesintoitsconstituentsinapurestateisanimportantprocessinchemistry.Theconstituentsofanymixturecanbeseparatedonthebasisoftheirdifferencesintheirphysicalandchemicalproperties,e.g.,particlesize,solubility,effectofheat,acidityorbasicityetc.
Someofthemethodsforseparationofmixturesare:
(1)Sedimentationordecantation.Toseparatethemixtureofcoarseparticlesofasolidfromaliquide.g.,muddyriverwater.
(2)Filtration.Toseparatetheinsolublesolidcomponentofamixturefromtheliquidcompletelyi.e.separatingtheprecipitate(solidphase)fromanysolution.
(3)Evaporation.Toseparateanon-volatilesolublesaltfromaliquidorrecoverthesolublesolidsolutefromthesolution.
(4)Crystallization.Toseparateasolidcompoundinpureandgeometricalform.
(5)Sublimation.Toseparatevolatilesolids,fromanon-volatilesolid.
(6)Distillation.Toseparatetheconstituentsofaliquidmixture,whichdifferintheirboilingpoints.
(7)Solventextractionmethod.Organiccompounds,whichareeasilysolubleinorganicsolventsbutinsolubleorimmisciblewithwaterformingtwoseparatelayerscanbeeasilyseparated.
1.3Atoms,MoleculesandCompounds
Thefundamentalunitofachemicalsubstanceiscalledanatom.ThewordisderivedfromtheGreekatomos,meaning“undivisible”or“uncuttable”.Anatomisthesmallestpossibleparticleofasubstance.
Moleculeisthesmallestparticleofasubstancethatretainsthechemicalandphysicalpropertiesofthesubstanceandiscomposedoftwoormoreatoms;agroupoflikeordifferentatomsheldtogetherbychemicalforces.Amoleculemayconsistofatomsofasinglechemicalelement,aswithoxygen(O2),orofdifferentelements,aswithwater(H2O).
Achemicalelementisapurechemicalsubstanceconsistingofonetypeofatomdistinguishedbyitsatomicnumber,whichisthenumberofprotonsinitsnucleus.Thetermisalsousedtorefertoapurechemicalsubstancecomposedofatomswiththesamenumberofprotons.UntilMarch2010,118elementshavebeenobserved.94elementsoccurnaturallyonearth,eitherasthepureelementormorecommonlyasacomponentincompounds.80elementshavestableisotopes,namelyallelementswithatomicnumbers1to82,exceptelements43and61(technetiumandpromethium).Elementswithatomicnumbers83orhigher(bismuthandabove)areinherentlyunstable,andundergoradioactivedecay.Theelementsfromatomicnumber83to94havenostablenuclei,butareneverthelessfoundinnature,eithersurvivingasremnantsoftheprimordialstellarnucleosynthesisthatproducedtheelementsinthesolarsystem,orelseproducedasshort-liveddaughter-isotopesthroughthenaturaldecayofuraniumandthorium.Theremaining24elementssoareartificial,orsynthetic,elements,whichareproductsofman-inducedprocesses.Thesesyntheticelementsareallcharacteristicallyunstable.Althoughtheyhavenotbeenfoundinnature,itisconceivablethatintheearlyhistoryoftheearth,theseandpossiblyotherunknownelementsmayhavebeenpresent.Theirunstablenaturecouldhaveresultedintheirdisappearancefromthenaturalcomponentsoftheearth,however.
Thenaturallyoccurringelementswerenotalldiscoveredatthesametime.Some,suchasgold,silver,iron,lead,andcopper,havebeenknownsincethedaysofearliestcivilizations.Others,suchashelium,radium,aluminium,andbromine,werediscoveredinthenineteenthcentury.Themostabundantelementsfoundintheearth’scrust,inorderofdecreasingpercentage,areoxygen,silicon,aluminium,andiron.Otherspresentinamountsof1%ormorearecalcium,sodium,potassium,andmagnesium.Together,theserepresentabout98.5%oftheearth’scrust.
ThenomenclatureandtheiroriginsofallknownelementswillbedescribedinChapter2.
Achemicalcompoundisapurechemicalsubstanceconsistingoftwoormoredifferentchemicalelementsthatcanbeseparatedintosimplersubstancesbychemicalreactions.Chemicalcompoundshaveauniqueanddefinedchemicalstructure;theyconsistofafixedratioofatomsthatareheldtogetherinadefinedspatialarrangementbychemicalbonds.Compoundsthatexistasmoleculesarecalledmolecularcompounds.Anioniccompoundisachemicalcompoundinwhichionsareheldtogetherinalatticestructurebyionicbonds.Usually,thepositivelychargedportionconsistsofmetalcationsandthenegativelychargedportionisananionorpolyatomicion.
Therelativeamountsoftheelementsinaparticularcompounddonotchange:
Everymoleculeofaparticularchemicalsubstancecontainsacharacteristicnumberofatomsofitsconstituentelements.Forexample,everywatermoleculecontainstwohydrogenatomsandoneoxygenatom.Todescribethisatomiccomposition,chemistswritethechemicalformulaforwaterasH2O.
Thechemicalformulaforwatershowshowformulasareconstructed.Theformulaliststhesymbolsofallelementsfoundinthecompound,inthiscaseH(hydrogen)andO(oxygen).Asubscriptnumberafteranelement'ssymboldenotes
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