英文化学元素周期表.docx

英文化学元素周期表.docx

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英文化学元素周期表

ThePeriodicTableofElements

byAnthonyCarpi,Ph.D.

In1869,theRussianchemistDmitriMendeleevfirstproposedthatthechemicalelementsexhibiteda"periodicityofproperties." Mendeleevhadtriedtoorganizethechemicalelementsaccordingtotheiratomicweights,assumingthatthepropertiesoftheelementswouldgraduallychangeasatomicweightincreased. Whathefound,however,wasthatthechemicalandphysicalpropertiesoftheelementsincreasedgraduallyandthensuddenlychangedatdistinctsteps,orperiods. Toaccountfortheserepeatingtrends,Mendeleevgroupedtheelementsinatablethathadbothrowsandcolumns. 

ThemodernperiodictableofelementsisbasedonMendeleev'sobservations;however,insteadofbeingorganizedbyatomicweight,themoderntableisarrangedbyatomicnumber（z）. Asonemovesfromlefttorightinarowoftheperiodictable,thepropertiesoftheelementsgraduallychange. Attheendofeachrow,adrasticshiftoccursinchemicalproperties.Thenextelementinorderofatomicnumberismoresimilar（chemicallyspeaking）tothefirstelementintherowaboveit;thusanewrowbeginsonthetable.  

Forexample,oxygen（O）,fluorine（F）,andneon（Ne）（z=8,9and10,respectively）allarestablenonmetalsthataregasesatroomtemperature.Sodium（Na,z=11）,however,isasilvermetalthatissolidatroomtemperature,muchliketheelementlithium（z=3）.Thussodiumbeginsanewrowintheperiodictableandisplaceddirectlybeneathlithium,highlightingtheirchemicalsimilarities.

Rowsintheperiodictablearecalledperiods. Asonemovesfromlefttorightinagivenperiod,thechemicalpropertiesoftheelementsslowlychange. Columnsintheperiodictablearecalledgroups. Elementsinagivengroupintheperiodictablesharemanysimilarchemicalandphysicalproperties. Thelinkbelowwillopenacopyoftheperiodictableofelementsinanewwindow.  

ThePeriodicTableofElements

ElectronConfigurationandtheTable

The"periodic"natureofchemicalpropertiesthatMendeleevhaddiscoveredisrelatedtotheelectronconfigurationoftheatomsoftheelements.Inotherwords,thewayinwhichanatom'selectronsarearrangedarounditsnucleusaffectsthepropertiesoftheatom.

Bohr'stheoryoftheatomtellsusthatelectronsarenotlocatedrandomlyaroundanatom'snucleus,buttheyoccurinspecificelectronshells（seeourAtomicTheoryIImoduleformoreinformation）.Eachshellhasalimitedcapacityforelectrons.Aslowershellsarefilled,additionalelectronsresideinmore-distantshells.

Thecapacityofthefirstelectronshellistwoelectronsandforthesecondshellthecapacityiseight.Thus,inourexamplediscussedabove,oxygen,witheightprotonsandeightelectrons,carriestwoelectronsinitsfirstshellandsixinitssecondshell.Fluorine,withnineelectrons,carriestwoinitsfirstshellandseveninthesecond.Neon,withtenelectrons,carriestwointhefirstandeightinthesecond.Becausethenumberofelectronsinthesecondshellincreases,wecanbegintoimaginewhythechemicalpropertiesgraduallychangeaswemovefromoxygentofluorinetoneon.

Sodiumhaselevenelectrons.Twofitinitsfirstshell,butrememberthatthesecondshellcanonlycarryeightelectrons.Sodium'seleventhelectroncannotfitintoeitheritsfirstoritssecondshell.Thiselectrontakesupresidenceinyetanotherorbit,athirdelectronshellinsodium.Thereasonthatthereisadramaticshiftinchemicalpropertieswhenmovingfromneontosodiumisbecausethereisadramaticshiftinelectronconfigurationbetweenthetwoelements.Butwhyissodiumsimilartolithium?

Let'slookattheelectronconfigurationsoftheseelements.

GroupIA

VIA

VIIA

VIIIA

Lithium

Oxygen

Fluorine

Neon

Sodium

ElectronConfigurationsforSelectedElements

Asyoucanseeintheillustration,whilesodiumhasthreeelectronshellsandlithiumtwo,thecharacteristictheyshareincommonisthattheybothhaveonlyoneelectronintheiroutermostelectronshell.Theseouter-shellelectrons（calledvalenceelectrons）areimportantindeterminingthechemicalpropertiesoftheelements.

Anelement'schemicalpropertiesaredeterminedbythewayinwhichitsatomsinteractwithotheratoms.Ifwepicturetheouter（valence）electronshellofanatomasasphereencompassingeverythinginside,thenitisonlythevalenceshellthatcaninteractwithotheratoms-muchthesamewayasitisonlythepaintontheexteriorofyourhousethat"interacts"with,andgetswetby,rainwater.

Lithium

Sodium

Anatom'svalenceshell

"covers"innerelectronshells

Thevalenceshellelectronsinanatomdeterminethewayitwillinteractwithneighboringatoms,andthereforedetermineitschemicalproperties.Sincebothsodiumandlithiumhaveonevalenceelectron,theysharesimilarchemicalproperties.

ElectronConfigurationShorthand:

ForelementsingroupslabeledAintheperiodictable（IA,IIA,etc.）,thenumberofvalenceelectronscorrespondstothegroupnumber.ThusLi,Na,andotherelementsingroupIAhaveonevalenceelectron.Be,Mg,andothergroup-IIAelementshavetwovalenceelectrons.B,Alandothergroup-IIIAelementshavethreevalenceelectrons,andsoon.Therow,orperiod,numberthatanelementresidesinonthetableisequaltothenumberoftotalshellsthatcontainelectronsintheatom.HandHeinthefirstperiodnormallyhaveelectronsinonlythefirstshell;Li,Be,B,andotherperiod-twoelementshavetwoshellsoccupied,andsoon.Towritetheelectronconfigurationofelements,scientistsoftenuseashorthandinwhichtheelement'ssymbolisfollowedbytheelement'selectronshells,writtenasaright-handparenthesessymbol"）".Thenumberofelectronsineachshellisthenwrittenafterthe）symbol.Afewexamplesareshownbelow.

Element

 ConfigurationShorthand

Hydrogen

      H）1e-

Lithium

      Li）2e-）1e-

Fluorine

      F ）2e-）7e-

Sodium

      Na）2e-）8e-）1e- 

Forfurtherdetails,thetablelinkedbelowshowstheelectronconfigurationsofthefirstelevenelements.

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PeriodicTableofElementsQuiz

"ThePeriodicTableofElements"Module

Visionlearning-aninteractivepracticeexercise.

窗体顶端

（1）DmitriMendeleevorganizedthechemicalelements:

（a）byincreasingatomicnumberandsimilarproperties

（b）byincreasingatomicweightandsimilarproperties

（c）bynumberofelectrons

（d）inalphabeticalorder

（2）Theelementsinthepresentperiodictablearearrangedaccordingtotheir:

（a）atomicmasses

（b）atomicnumber

（c）atomicweight

（d）massnumber

（3）Averticalcolumnintheperiodictableiscalleda:

（a）branch

（b）group

（c）period

（d）valence

（4）Ahorizontalrowintheperiodictableiscalleda:

（a）branch

（b）group

（c）period

（d）shells

（5）Themajorityoftheelementsintheperiodictableare:

（a）metalloids

（b）metals

（c）noblegases

（d）nonmetals

（6）WhatdoesBohr'stheorystate?

（a）Electronsarelocatedrandomlyaroundanatom'snucleus

（b）Electronsdon'toccuratallinatoms

（c）Electronsoccuraroundthenucleusinelectronshellsthathavealimitedcapacity

（d）Electronsoccurinshellsofunlimitedcapacity

（7）Whatisthecapacityofthefirstelectronshell?

（a）eight

（b）sixteen

（c）three

（d）two

（8）Whichofthefollowingistheelectronconfigurationforcarbon:

（a）C）2e-）4e-

（b）C）2e-）6e-

（c）C）2e-）8e-）2e-

（d）Ca）2e-）8e-）2e-

（9）Elementsinthesomegrouphave:

（a）similarsymbols

（b）thesamenumberofelectrons

（c）thesamenumberofneutrons

（d）thesamenumberofvalenceelectrons

（10）Elementsinthesameperiodhave:

（a）graduallychangingproperties

（b）identicalchemicalproperties

（c）similarsymbols

（d）thesamenumberofneutrons

（11）Whichelementisclassifiedasmetalloid?

（a）Ca

（b）Cl

（c）Si

（d）Zn

（12）Howmanyvalenceelectronsdoescalciumhave?

（a）eight

（b）one

（c）twenty

（d）two

（13）Howmanyvalenceelectronsdoesboronhave?

（a）four

（b）one

（c）three

（d）two

窗体底端

（注：

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